Chinook winds in the Colorado High Plains region

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ProQ uest Number: 10295201

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[F r o m A m e r ic a n J o u r n a l o f S c ie n c e , V o l.

XXXV,

F ebruary,

1938]

C H IN O O K W IN D S IN N O R T H E R N C O L O R A D O .

R O N A L D L. IV E S .

Submitted to the Faculty of the Graduate School in partial fulfillm ent of the requirements for the degree, Doc­ tor of Philosophy, Department of Geography, Indiana Uni­ versity.

C H IN O O K W IN D S IN N O R T H E R N C O L O R A D O . R O N A L D L. IV E S . A B ST R A C T .

Chinook winds have long been known as a feature of the clim ate of the Rocky Mountain Region. Recently observed temperatures in the mountains during Chinook winds differ considerably from those called for by the generally accepted explanation of these winds. These temperature differ­ ences, and their relation to evaporation and wind velocity, are described in this paper. A partial explanation of the difference between theoretical and observed temperatures is presented, IN T R O D U C T IO N .

S everal tim es d u rin g a norm al w in ter, C h in o o k w in d s blow o u t o f th e R ocky M o u n ta in s on to th e a d ja c e n t p lain s to th e east, rem o v in g m uch o r all o f the snow , d o in g m o re o r less p ro p erty dam age, an d ra isin g th e te m p e ra tu re m a n y d egrees in a few h o u rs. T h ese w inds alm ost alw ays o ccur a f te r a p erio d o f subzero tem p eratu res, w hich usually follow s a sn o w ­ storm . P re d ictio n o f C hinook w inds by o rd in a ry fo re c a st­ in g m ethods is difficult, if n o t im possible. D E SC R IP T IO N OF A T Y P IC A L C H IN O O K W I N D .

A lth o u g h te m p eratu res, w ind velocities, a n d precip itatio n b efo re and d u rin g C hinook w inds are d iffe ren t fo r each w in d , c ertain conditions a re com m on to all o f them . A few h o u rs p rio r to the b e g in n in g o f a C hinook w ind, te m p e ra tu re s on both sides o f the ra n g e are low, usually som e d eg rees below zero. T em p eratu res in the m ountains, w hile low, a re n o t m any d egrees low er th a n those in the flatlands a d ja c e n t to th e ran g e . A b aro m e tric lozv, m o v in g rapidly so u th w a rd alo n g th e eastern slope o f the ran g e, at a velocity o f m o re th a n fo rty m iles an h our, com m only im m ediately precedes th e b e g in n in g o f the w ind. T h is lozv probably in itiates th e tra n s -ra n g e air m otion. Soon, a ir begins to m ove rapidly across th e ran g e , fro m west to east. T e m p e ra tu re s fall several d eg rees on both sides o f th e range. O n the w in d w a rd slope, snow is m oved m echanically fro m flat are a s an d piled into valleys n e a r th e crest o f the range. Som e new snow falls n ea r th e crest o f the ran g e. O n 138

Chinook W inds in Northern Colorado.

139

th e leew ard slope, snow is rap id ly rem oved, so m e o f it b y sub lim atio n , m o re o f it m echanically (m u c h o f th is is b lo w n h ig h in to th e a ir, th e n s u b lim a te d ). A fte r som e tim e, u su ally several h o u rs, th e w in d reaches its m a x im u m velocity, w hich com m only exceeds six ty m iles a n h o u r. M u ch o f th e snow on th e plains a n d on th e leew ard side o f th e ra n g e has been evap o rated , m o st o r all o f th e snow h as been rem oved fro m th e flatlan d s on th e w in d w a rd side o f th e ra n g e an d piled n e a r th e sum m it. T h e te m p e ra tu re rises rapidly, o fte n a t th e ra te o f tw e n ty o r m o re d eg rees a n h o u r, on b o th th e leew ard plain s an d th e leew ard slopes. T e m p e ra ­ tu re s o n th e w in d w a rd flatlan d s a n d slopes rise m o re slow ly, a n d u su a lly only a few degrees. A few h o u rs a f te r th e te m p e ra tu re s o n th e leew ard side o f th e ra n g e rise, th e w in d dies dow n, a n d ceases. S om e m iles east o f th e ran g e , th e w in d s a re less violent, a n d th e te m p e ra ­ tu r e changes less. A C hinook w in d th a t is s tro n g en o u g h to dem olish o u th o u se s in B o u ld er, C olorado, f o r exam ple, is barely stro n g en o u g h to m ove tum blew eeds o n th e plains tw e n ty m iles to th e east. T H E O R E T IC A L C O N SID E R A T IO N S .

C hinook w in d s h av e been d escribed b y m a n y te ac h ers o f clim atology, an d by som e w rite rs o f te x tb o o k s, as ad iab a tic phenom ena. T h is th ey ca n n o t be, f o r te m p e ra tu re s a t equal elevations on opposite sides o f th e ra n g e shou ld be equal u n d e r th is ex p lan atio n . A tte m p ts to exp lain C hinook w in d s as w et o r pseu d o a d iab a tic phen o m en a a re m o re successful. W h e n th e h e a t o f v a p o riz a tio n ( a n d u sually fu sio n ) ra d ia te d to th e r is in g a ir by th e co n d e n sin g (a n d u sually fre e z in g ) w a te r v ap o r on th e w in d w a rd slope, is considered, th e w a rm th o f th e la ter stag es o f a d escen d in g C hinook w in d is no lo n g e r a m y stery . F IE L D O B SE R V A T IO N S.

D u rin g th e w in te r o f 1932 , th e ta k in g o f a series o f p h o to ­ g ra p h s o f snow co n d itio n s on th e glaciers o f th e C o lo ra d o F ro n t R a n g e w as planned. F ro m te m p e ra tu re s an d relativ e h u m id itie s d eterm in e d in B oulder, p ro b ab le m in im u m te m p e ra ­ tu re s in th e m o u n ta in s w ere calculated, an d cam p in g eq u ip ­ m en t chosen accordingly, a la rg e m a rg in o f sa fe ty b ein g

THURSDAY 6 g

SA TU ROAY

FRi DAY

+«

T h e rm o g ra p h -B a ro g ra p h

C h a rts

fo r

F e b ru ary

7t h

and

8 th ,

1936.

D uring this Chinook wind, air motion began at about five o ’clock on the morning of the eighth, and stopped late in the afternoon. T his record was made m Boulder, Colorado, at an elevation of 5,300 feet. T he instruments were about 6,000 feet from the front of the range, on the plains. T h e temperature change during this storm w as 60 degrees. In Denver, farther from the mountains, it was 58 degrees, w hile in Cheyenne, W yom ing the change w as only 26 degrees. A w ay from the mountains, although within th e only 18 de^r* e s*-orrn> N orth Platte, the temperature change w as

Chinook W inds in N orthern Colorado.

141

allow ed. D u rin g a C h in o o k w ind, p ro b ab le h ig h c o u n try te m p e ra tu re s o f a b o u t te n d eg rees below zero w ere p red ic ted by calculations. T e m p e ra tu re s in th e v ic in ity o f e ig h ty d eg rees below zero w ere e n c o u n te re d a t 11,000 fe e t; th e re su lta n t severe fre e z in g effectively sto p p in g the p ro je c te d p h o to g ra p h ic w o rk . F ro m Ja n u a ry , 1933 , u n til M arch , 1937 , co n d itio n s in th e h ig h c o u n try w ere observed in a n e ffo rt to d eterm in e a m eans o f p re d ic tin g te m p e ra tu re s d u rin g C h inook w in d s. W h ile th e o b se rv a tio n s leave m uch to be d esired, b ein g m ad e u n d e r ad v erse conditions, an d a t th e expense o f m u ch fro stb ite , th e g en e ral conclusions d ra w n fro m th em seem to shed som e lig h t on th e problem . G E N E R A L C O N C L U S IO N S .

T e m p e ra tu re s observed on the w in d w a rd side o f th e ra n g e a g re e q u ite closely w ith th o se calculated fo r w e t ad iab a tic co n ­ d itio n s. I t is probable th a t te m p e ra tu re s observed u n d e r b e tte r conditions, w ith m o re accu rate in stru m e n ts, will, w h en c o r­ rected fo r the influence o f local to p o g rap h y , ag re e even m o re closely w ith th o se pred icted by theo ry . T h e coldest point, d u rin g th e early p a r t o f a C hinook, w hile u n sh e lte re d snow still rem a in s on the leew ard slopes, is n o t a t th e su m m it o f th e ran g e , as called f o r by a d iab a tic th e o ry , b u t som e th o u sa n d s o f feet do w n the leew ard slope, th e ex act location v a ry in g fro m h o u r to h o u r, an d g ra d u a lly ap p ro a ch in g th e crest as th e snow disappears. L ocal to p o g ra p h y seem s to d eterm in e th e in itial p o sitio n o f the coldest p o int. R E V ISE D E X P L A N A T IO N .

F ro m th e su m m arized field o b serv atio n s it ap p ears th a t n eith er th e d ry n o r th e w et ad iab atic th e o ries giv e an en tirely s a tisfa c to ry ex p lan a tio n o f te m p e ra tu re ch an g es during* a C hinook w ind. T h e ex p lan a tio n h ere p rese n ted satisfies all conditions k n o w n to th e w rite r. A n y tra n s -ra n g e w in d m ay becom e a C hin o o k w in d if th e risin g a ir receives h e a t fro m the co n d en satio n (a n d u su ally fre e z in g ) o f som e o f its m o istu re d u r in g its p ro g re ss fro m th e flatlands to th e su m m it o f the range. T h e am o u n t o f h ea t received by th e asce n d in g a ir m ay be ro u g h ly calculated fro m th e te m p e ra tu re an d relative h u m id ity a t any k n o w n

567729

Ronald L . Ives.

142

altitude, p ro v id ed the elevations o f th e flatlan d s an d o f th e sum m it o f the ran g e are k n o w n ( 1 ) . T h e te m p e ra tu re o f the d escending a ir depends u p o n its initial te m p e ra tu re ( a t th e su m m it o f th e r a n g e ), th e am o u n t o f its descent, and th e a m o u n t o f h e a t rem ov ed fro m it by th e sublim ation o f snow d u rin g its descent o f th e leew ard slope. S ublim ation occurs only in th e th in zone o f a ir n e a r th e snow surface. H ence, su rfa c e a ir te m p e ra tu re s u su ally a re v ery m uch low er th a n a ir te m p eratu re s only a few ro d s above th e snow . W h e n all o f th e u n sh eltered snow on th e leew ard slopes has been “ ea te n ” by th e C hinook, su rfa c e a ir te m p e ra tu re s approach those called fo r by ad iab atic th eo ry . T h u s, the w in d fro m th e m o u n ta in s is cold d u rin g th e early stages of a C hinook because o f th e h e a t lost by th e low er layers o f m o v in g a ir as th e u n sh eltered snow on th e leew ard slopes is sublim ated. L a te r, w hen th is snow is gone, th e w in d becom es w arm , fo r little o f th e h ea t g ain ed b y th e a ir d u r in g its desiccation on the w in d w a rd slope is w ith d ra w n d u r in g th e descent o f th e leew ard slope. ACKNOW LEDGM ENTS.

A b o u t 200 resid e n ts o f B o u ld er a n d G ran d C ounties, C olorado, g av e in fo rm a tio n an d assistan ce d u r in g th is stu d y . T h e w rite r is especially indebted to D r. H . A. H o ffm e iste r, o f th e D ep a rtm en t o f G eology, U n iv e rsity o f C olorado, f o r th e use o f th e th e rm o g ra p h -b a ro g ra p h re c o rd ; to D r. an d M rs. C harles E . Snow , o f L akew ood, C olorado, fo r assistan ce in the fie ld ; and to M a jo r A . H . T hiessen, o f W a sh in g to n , D . C. f o r discussion and criticism o f this paper. W e a th e r m ap s an d in fo rm a tio n w ere supplied on several occasions by th e U n ite d S tates an d C a n ad ian W e a th e r B ureaus. B IB L IO G R A P H Y . (1 ) Humphreys, W . J . : P hysics of ihe A ir . volume pp. 26-39; Chinook winds pp. 207-208. W a s h in g t o n ,

D. C.

Temperature, pressure, and

Abstracts of Papers PROORAV C*1 THE A 6 t h W P ’AT, ’ -.MTTMO, AH W T A "’! . V '■p f P - . O O H . M '- P P f j

CLARK nKT^KRKTT''', "’ORCTTT’-'R, '" ;S S ,

■'•'■'K*, 5 - fl, 1R0.

R E S O U R C E S A N D P H Y S IC A L G E O G R A P H Y R o n a l d L . I v e s — Frequency of Chinook W i n d s in the Colorado Hi gh Plains Region.

Statistical analysis of the frequency of chinook winds, as reported by various agencies, using various criteria, is here presented, using data for the Fraser-D enver trajectory, during the period 1930-1948. Chinook winds, as defined by m eteorological criteria, occurred 39.26 times per average year during this time. Frequency of occurrence was greatest in the winter, m axim um month being January ; a secondary m axim um was noted in July. Chinook winds w ere least frequent in May and June, with a secondary minimum in Septem ­ ber. Chinook winds, as reported by the residents of the plains, who observed only snow removal and temperature rise, were more num erous than those defined by stricter meteorological criteria but had a similar temporal distribution. T hese winds are identical w ith W arm W esterlies as reported by m eteorologists, and occur 52.30 tim es per average year. Complete classification of the various westerly winds of the high plains region is here presented, with charts show ing the frequency of chinook and other w esterly winds and the criteria used in classifying them.

[23] T H U R S D A Y A F T E R N O O N , A P R IL 6 2 : 0 0 P.M .

G e o g r a p h y B u il d in g

RESOURCES AND PHYSICAL GEOGRAPHY

R o n a l d L. I v e s , Indiana U niversity.

“Frequency of Chinook W i n d s in the Colo­

rado H ig h Plains Regi on. ”

S u b m itte d to th e F a c u lty o f th e G ra d u a te S ch o o l in p a rtia l fu lfillm e n t o f th e r e q u ir e m e n ts fo r th e d e g r e e , D o c to r o f P h i­ lo so p h y , in th e D e p a r tm e n t o f G e o g r a p h y , In d ia n a U n iv e r s ity .

15 minutes

Submitted to the Faculty of the Graduate School in partial fulfillm ent of the requirements for the degree, Doc­ tor of Philosophy, Department of Geography, Indiana Uni­ versity. [R e p rin te d fro m the B u lle tin of the A m eric a n M eteorological S o c iety , N o v em b e r, 1 9 3 9 , vol. 2 0 , p p . 3 9 5 -3 9 6 .]

A C h in o o k C r e s t C lo u d o v e r t h e C o lo r a d o F r o n t R a n g e P h o to g r a p h

I n fr a -r e d

R onald L. I ves B o u ld e r, C ol.

P h otograph ic D a ta :— Taken at 11:40 A.M. (M S T ) Dec. 2, 1938 from steps o f W om en’s D orm i­ tory, U n iv e r sity o f Colorado, Boulder, Colo. 91 in. len s, used a t F 32, 1 sec. E a st­ man IR-1 p lates, W ratten F filter. D evelopm ent by T & T in E astm an DK -76. H alf-ton e reduced from an 8 diam. enlargem ent from part o f the plate. T opograph ic d a t a :— E levation o f cam era station 5300 ft. B earin g o f c. 1. o f cam era N . 62 deg. W. B ase o f cloud at 9200 ft. (telephoned report from fo r est r a n g e r). Top o f cloud a t 16,500 ft. scaled photograph, top o f cloud assum ed to be over continental divide, 20 m iles from cam era. N earest point o f cloud 15 m iles from Boulder (direct o b ser v a tio n ). F a rth est point o f cloud (w estern m argin) 45 m iles from Boulder (tele ­ phoned report from G ranby and H ot Sulphur Sp rin gs.) General level o f C ontinental Divide in th is region is 13,000 ft.

M eteorological D a t a :— Boulder— w inds erratic tem p. 40°. Above Boulder (elev. 8,000 ft. obs. m ade at 1:30 P .M .)— w inds from w est, g u sty , violen t; tem p. 4 2°. G ranby (telephoned reporit)— 18° m ax. fo r day, 5° m in; w ind s from w est, “blow in g lik e hell”, base o f cloud at 9,200 ft. approx. Grand Lake (telephoned rep ort) — no wind, .1 in. precip., m in. temp. 6°, max. 31°, 7 in. snow on ground. Other D a t a :— A bout 3 in. o f snow fe ll during th is storm , over an area o f unknown len gth, about 20 m iles w ide (from continental divide w e s t). T his is roughly .15 in. in w ater equiva­ lent. About i in. of snow w as removed from th e leew ard slopes b y sublim a­ tion (.025 in. m elted) over an area o f unknown len gth and 8 m iles w ide (from the continental divide e a s t). A ll un sheltered sn ow w as removed from th e footh ills above :8,000 ft. eleva­ tion by th is wind. Snow below 8,000 ft. w as not affected. A local aviator reports th a t w inds betw een 8,500 ft. and 10,500 ft. w ere in excess of 100 mph, but th a t above th is there w as little w ind. This w ind ap p aren tly “h it th e ground” about tw elve m iles ea st o f Boulder, on th e p lains, w here it w as warm ( ca. 5 0 °) and had a velocity in the neighborhood o f 25 mph. D u rin g th is wind, long-distan ce telephone lin es w ere very noisy, sta tic in terfered w ith radio program s, and w ire fences ea st o f tow n w ere chai'ged up enough to give a very sligh t shock when touched.

EXCERPT FROM

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e o g r a p h ic a l

R

e v ie w

PUBLISHED BY

T h e A m e r ic a n G e o g r a p h ic a l S o c ie t y of

N

ew

VOL. 3 I

York

NO. I

19 Hi

Subm itted to th e F aculty of the G raduate School in p artial fulfillm ent of th e requirem ents fo r the degree, Doc­ to r of Philosophy, D epartm ent of Geography, Indiana U ni­ versity.

COLORADO F R O N T R A N G E C R E ST CLO U DS A N D R ELA TED PH ENO M ENA* R o n a ld L. Iv e s

IN C E th e tim e of th e first se ttle m e n t of th e foothills of th e C olorado F ro n t R ange, in th e m iddle of th e la st ce n tu ry , th e ap p e aran c e of a crest cloud over th e range has been in te rp re te d — w ith g re a t accu rac y — as an in dication th a t “ so m eth in g 's going to happen. S tu d ies of these clouds an d of th e w ea th er changes following th e ir ap p earan ce, d u rin g th e y ears 1932 to 1939 inclusive, h av e disclosed a n u m b e r of d istin c t crest-cloud types and h ave supplied m a n y d a ta relativ e to b o th th e ir causes an d th e w ea th er changes th e y presage. T h e d a ta on w hich these stu d ies are based are o b serv atio n al, of an accuracy b est classified as “ careful rec o n n aissan ce .” W e ath er p red ictio n s using these d a ta and all o th e r av ailab le in fo rm atio n are a b o u t 85 per ce n t accu rate. T h e 15 per ce n t erro r in d icates th a t all is n o t y e t know n a b o u t crest clouds. P red ictio n failures, wrhen n o t due to m isin te rp re ta tio n of d a ta , m ay be caused by u n d etec ted local effects produced b y canyon “ ch im ­ ney c u r r e n ts ” and related m inor air drifts, of w?hich th e re m ay be m an y in a v ery few- sq u are m iles of m o u n ta in c o u n try ; or b y u n d etected , an d largely u n d etec tab le, m ix tu re of the “ su rfa c e ” air, in w hich th e clouds are form ed, w ith th e cold, rap id ly m oving a ir of th e “ trad e wind s tr a t u m ,” a t a ltitu d e s above 16,000 fee t.1 W e a th e r changes ac co m p an y in g crest clouds o th e r th a n th o se of th e “ cold f r o n t ” ty p e seldom d irec tly affect areas m uch m ore th a n 40 m iles from the su m m it of th e range. T h e in d ire ct effects, how ever, are felt th ro u g h o u t th e w estern p a r t of th e U nited S ta te s ; for in th e areas near th e C o n tin en tal D ivide, wrhere these clouds occur, are th e sources of th e M issouri, P la tte , A rkansas, a n d C olorado R iv ers and th e Rio G rande. T h e phenom ena rep o rted here were observed in th e C olorado F ro n t R ange area. R ough reconnaissances of o th e r m o u n tain areas in th e w estern U nited S ta te s in d ic ate th a t sim ilar, b u t n o t identical, p h e ­ nom ena occur elsew here. * T h e w r ite r is in d e b te d to P ro fe s s o r H , A , H o ffm e iste r, U n iv e rs ity of C o lo rad o , fo r m a k in g a v a ila b le th e in s tr u m e n t tra c e s a n d o th e r d a ta u n d e r his c a re . D r. L o u is O. Q u a m of th e U n iv e rs ity g r e a tly e x p e d ite d t h e w o rk w ith m a n y u s e fu l a n d in fo r m a tiv e d isc u ssio n s of th e fa c to rs in v o lv e d . T h e w r ite r is g ra te fu l to m a n y m e m b e rs of th e U n iv e rs ity of C o lo ra d o H ik in g C lu b , p a rtic u la rly J o h n C o y le a n d T h o m a s C la y , fo r th e ir a s sis ta n c e , o fte n a t g re a t p e rs o n a l in c o n v e n ie n c e a n d d isc o m fo rt, d u rin g field s tu d ie s of m o u n ta in s to rm s. W ith o u t th is h e lp it w o u ld h a v e b een im p o ssib le to o b ta in m a n y of th e p h o to g ra p h s a n d m a n y of th e d a ta in c lu d e d h ere. 1 R . L. Iv e s: W e a th e r P h e n o m e n a of th e C o lo ra d o R o c k ie s. J o u n i. F r a n k lin In st., V ol. 226, 1938, p p . 6 9 1 - 7 5 5 : refe ren c e o n p . 721. U se of t h e te rm “ tr a d e w in d s t r a t u m " is b a sed o n H u m p h r e y s ' d e fin itio n of a tra d e w in d as one t h a t blow s s te a d ily , re g a rd le s s of d ire c tio n o r a ltitu d e .

THE

24

G EO G RAPH ICAL

R EVIEW

B O U L D ER . C O L O R A D O , M ARCH 12, 1 9 3 4

T H E R M O G R A PH

- BA RO G RA PH -E L E V A T IO N

5300 '-

H Y G RO G R A PH

F i g . i (a b o v e )— I n s tr u m e n t tra c e s d u rin g a ty p ic a l c h in o o k w in d . M a x im u m w in d v e lo c ­ i ty w a s b e tw e e n 7 a n d 10 a .m . R e c o rd s fu rn is h e d b y t h e D e p a r tm e n t of G eo lo g y , U n iv e rs ity of C o lo rad o .

A B S O L U T E H U M ID IT Y IN A R B I T R A R Y U N I T S

F ig . 2 (rig h t) — C h a n g e s in a b s o lu te h u m id ity d u rin g a ty p ic a l c h in o o k , a s c a lc u la te d fro m th e d a ta of F ig u re 1.

C h in ook C rest C louds

F rom tw o to m ore th a n ten tim es d u rin g an av erag e w in te r v io len t, desiccating w arm w inds sw eep dow n from th e m ain range, rem oving m uch or all of th e snow from th e plains a d ja c e n t to th e foothills an d doing considerable d am ag e to p ro p e rty . D u rin g th ese w inds te m p e ra ­ tu res rise sh a rp ly ; rises of m ore th a n 40° F . h av e been rep o rted , in one case 6o°.2 T h e changes in te m p e ra tu re , air pressure, an d h u m id ity d u rin g a ty pical chinook w ind are show n in F igures 1 a n d 2. 2 R . L . Iv e s: C h in o o k W in d s in N o r th e r n C o lo rad o , A m e r . J o u r n . o f S c i., S er. 5, V o l. 35, 1938, p p . 1 3 8 -1 4 2 ; “ R e m a rk a b le C h in o o k in A lb e r ta ,” B u ll. A m e r . M eleorol. Soc., V ol. 19, 1938, p p . 4 0 8 -4 0 9 ,

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M e c h a n ic s o f a C h in o o k

T h e ac tu a l m echanics of th e chinook, as d eterm in e d from field o b se rv a tio n s an d in stru m e n ta l records, are m uch m ore com plex th a n th e s ta n d a rd d escrip tio n s ind icate. C hinooks, as gen erally d efin ed ,3 differ from o th e r tra n sm o u n ta in w inds in th e resp ect th a t, as a resu lt of th e release of h e a t by co ndensation of som e of th e m o istu re in th e a ir rising on th e w indw ard side of th e range, te m p e ra tu re s, level for level, are higher to leew ard th a n to w indw ard. T h is co n d en satio n pro duces th e crest cloud ch a ra c te ristic of these w inds.

F ig . 3— W e st-e a s t c ro ss se ctio n of th e C o lo ra d o F r o n t R a n g e , a b o u t la t i tu d e 40° N ., sh o w in g o c c u rre n c e s d u rin g a ty p ic a l c h in o o k w ind.

G eneralized conditions du rin g a typ ical chinook in th e so u th ern R ocky M o u n ta in s (at a b o u t 40° N .), as d eterm in e d from field o b se rv a­ tions, are show n in F igure 3. T h is diag ram d ep icts a “ p u r e ” chinook, n o t ap p reciab ly in terfered w ith b y the num erous local air circu latio n s th a t are u sually p resent. A ny tra n sm o u n ta in w ind m ay becom e a chinook if it suffers a n e t loss of m oisture d u rin g its tra n s it of the range. U nless th e w ind loses m oisture, its te m p e ra tu re , level for level, will be th e sam e on b o th sides of the range, except for the influence of v ario u s local facto rs— su blim ation, air m ixture, friction, rad ia tio n — usu ally of m inor im p o r­ tan ce and n o t m easurable w ith s ta n d a rd in stru m e n ts. F leat released by the condensation, an d usually freezing, of m o istu re carried b y th e air is absorbed by it. T h is causes th e air of a chinook to be w arm er an d d rier to leew ard th a n to w indw ard an d acco u n ts for its “ snow e a tin g ” ch a racteristics. S tudies of the physical th e o ry of chinooks by H u m p h rey s4 an d o th ers suggest th a t th e w ind is a “ m ixed ” phenom enon, n eith er w holly a d ia b a tic nor w holly “ p se u d o ad ia b atic. ” S hould th e te m p e ra tu re changes d u rin g the tra n s it of a tra n sm o u n ta in w ind be a d ia b a tic (no h e a t gained or lost b y th e m oving air), no p rec ip ita tio n from it could occur, an d th e air, level for level, w ould h av e th e sam e te m p e ra tu re 3 \V. J . H u m p h r e y s : P h y s ic s of th e A ir, P h ila d e lp h ia , 1920, p p . 2 0 9 -2 1 0 . * H u m p h re y s , op. cil.. p p . 2 0 9 -2 1 0 a n d 2 5 4 -2 6 3 .

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on b o th sides of th e range. T h is occurs w hen th e tra n s m o u n ta in w inds are d ry an d explains th e ra r ity of su m m er chinooks in th e so u th e rn R ocky M o u n ta in s. S im ilarly, w hen som e condensation, b u t no p rec ip ita tio n , ta k e s place n ea r th e crest of th e range an d th e cre st cloud so form ed is carried over th e su m m it an d ree v ap o rate d , th e w ind, so far as sta tio n s far dow n th e m o u n tain flank are concerned, is tru ly a d ia b a tic , an d hence n o t a chinook. Such w inds are v ery com m on in th e R o ck y M o u n ta in region. W hen p rec ip ita tio n ta k es place, usually as snow, som e of th e h e a t th u s released to th e air is la te r rem oved by su b lim atio n of snow on th e leew ard slopes. T h u s, th e o ry an d observ atio n al d a ta concerning a chinook w ind ca n n o t be b ro u g h t in to ag reem en t unless a n u m b e r of s e p a ra te effects are considered. T h e p rese n t p au c ity of in stru m e n ta l sta tio n s m akes ac cu rate an d com plete o b serv atio n s n early im possible; hence d is­ ag reem en t betw een rep o rted and calcu lated te m p e ra tu re changes is considerable. C a u s e s o f C h in o o k s

C hinooks, like o th e r w inds, are caused b y p ressu re differences in th e atm o sp h ere. S tu d ies of w ea th er conditio n s ju s t preceding chinook w inds indicate th a t th e in itia to ry p ressu re differences are v ery slight, an d th is suggests th a t th e “ lo w s” to leew ard are “ oc­ c lu d e d ” (shaped like a w edge, w ith th e apex a t or n ea r th e surface an d th e base som ew here abo v e th e surface). C hinooks h av e often occurred from 24 to 60 ho u rs a fte r th e passage of a cold fro n t. T h is suggests th a t th e p ressure difference in itia tin g th e w ind is related to th a t w ithin th e cold a ir m ass a n d m ay be th e norm al in te rn al g ra d ie n t of th a t m ass, p ro b ab ly locally a c c e n tu a te d by th e “ b arrier e ffe c t” of th e m o u n ta in range, w hich te n d s to p roduce a v ery slight “ h ig h ” to w indw ard a n d a corresp o n d in g sm all “ lo w ” to leew ard. P re se n t d a ta do n o t ju stify an y definite rules for p red ic tin g ch i­ nooks. T h e b est rule to d a te is th a t a chinook is likeliest to occur w hen th e cen ter of an appro ach in g cold air m ass is a b o u t 50 m iles from th e crest of th e range. T h e d u ra tio n of th e w ind is a p p ro x i­ m ately th e tim e necessary for the cen ter of th e air m ass to trav e l 50 miles. R e ta rd a tio n of its m otion by to p o g rap h ically in d u ced local air cu rre n ts is to be expected, some sto rm s being “ h u n g u p ” b y th e m o u n ta in s for m a n y hours, som etim es for several d ay s. W h en th e m ag ­ n itu d e s and m otions of th e air m asses bringing cold w aves to th e R ocky M o u n ta in region are considered, it will be n o ted th a t th is rough rule, based on field observations, is in ra th e r close ag re em e n t w ith th e air m otions th a t should ta k e place if th e pressure differences causing

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Chinooks w ere those w ithin th e air m ass, a c c e n tu a te d so m ew h at b y to p o g rap h ic influences. O ften a very slight b aro m e tric “ lo w ” has been recorded on th e lee­ w ard side of a m o u n ta in range ju s t before th e beginning of a chinook. T h is h as been classified as th e “ lo w ” in itia tin g th e air m otion. R ecen t o b se rv a tio n s suggest, how ever, th a t this is a “ seco n d ary lo w ,” induced b y a ir m otion across th e m o u n tain s, a n d hence is a p ro d u ct, ra th e r th a n th e cause, of chinooks. C h a r a c t e r is t ic s o f t h e W in d w a r d A ir

On th e w indw ard side of a m o u n ta in range, du rin g a chinook w ind, th e m oving air below th e crest-cloud zone is sim ilar to th a t of a n y o th e r w ind. A considerable te m p e ra tu re range is possible, an d th e h u m id ity of th e air m ay v a ry w ith in ra th e r w ide lim its, th o u g h it is usu ally m oist, so th a t th e w ind is “ r a w .” In th is zone (Fig. 3, le ft side, betw een 8000 a n d 10,000 feet) te m p e ra tu re s decrease w ith increasing a ltitu d e a b o u t as a d ia b a tic calculations indicate. S lig h t d ev iatio n s from th e th eo retical values a re to be expected, as a resu lt of su b lim atio n b o th of snow on th e g round an d of snow falling in to th e m oving air from th e crest-cloud zone ab o v e it. As th e m oving air is usually b o th cold an d m oist, an d as its m oistness increases w ith a ltitu d e , th e am o u n t of su b lim atio n should be v ery slight— a conclusion su p p o rted b y n um erous field o b servations. M uch of th e supposed su b lim atio n a ttr ib u te d to th e w indw ard air of a chinook is a c tu a lly d riftin g , w hich te n d s to rem ove snow from level surfaces, such as highw ays, an d to d ep o sit it o u t of sig h t in gulches an d o th e r are as of m ark ed relief. O ccasionally th e w indw ard a ir of a chinook, below th e crest-cloud zone, carries supercooled w ate r dro p lets, w hich, on colliding w ith a h a rd surface, such as a rock ledge or th e w indshield of an auto m o b ile, “ flash ” in to ice. S im ilar supercooled d ro p lets h av e been n o te d acco m ­ p anying dense valley fogs in the areas w here chinooks are co m m on; an d u n d er slightly d ifferent conditions th e y produce h eav y in c ru sta ­ tions of rim e on high pinnacles near th e crest of th e range. S u p e r­ cooled d ro p lets visible to th e naked eye h av e been observed d u rin g chinooks w hen the air te m p e ra tu re w as as low as -2 0 ° F. C h a r a c t e r is t ic s o f t h e C r e s t -C l o u d Z o n e

D uring a ty p ic al chinook, a crest cloud, exten d in g from th e ap p ro x i­ m ate level of condensation on th e w indw ard side of th e ran g e to a few th o u san d feet to leew ard of th e crest, is usually p resen t. B etw een th e base of the crest cloud and th e land surface is a cloudless zone 100 feet or m ore thick, occupied b y a chaos of sw irling snow flakes, pine needles, gravel particles, an d th e “ sw ee p in g s” of th e w indw ard side

F ig . s F ig . 4 — A ty p ic a l c h in o o k c re s t c lo u d o v e r t h e C o lo ra d o F ro n t R a n g e . T h is c lo u d , r6 m ile s fro m th e c a m e ra , c o m p le te ly e n s h ro u d s th e m a in ra n g e , e x te n d in g to a h e ig h t of a b o u t r6 ,3 0 o fee t a b o v e sea level. F ig . S—V ie w u p w a rd fro m b e n e a th a c h in o o k c re s t c lo u d . T h is p h o to g ra p h , ta k e n a t tim b e r lin e (11,000 fe e t), lo o k in g w e s tw a rd a n d u p w a rd , sh o w s th e " w in d o w s " b e tw e e n t h e v a rio u s c o m p o n e n ts of t h e c re s t cloud.

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29

of th e range. T h e to p of th e cre st cloud (Fig. 4) is m ore o r less cy lin ­ drical, its m axim um a ltitu d e being a t th e line of “ ta n g e n c y ” of th e crest cloud an d th e base of th e “ tra d e w ind ” s tra tu m . In th e C olorado F ro n t R ange area, a b o u t 45 m iles n o rth w e st of D en v er, th e av erag e m axim um a ltitu d e of th e to p of a chinook cre st cloud is ab o u t 16,000 feet above sea level. As the crest of th e range averag es a b o u t 13,000 feet, a thickness of 3000 feet is suggested for th e w ind s tra tu m . W hen seen from a d istan c e of 15 to 20 miles, as in F igure 4, th e cre st cloud a p p e ars as a solid, m otionless cum u lu s of g re a t d en sity . A ctually, as field o b serv atio n s h av e d eterm in ed , it is a sw arm of d iscrete, te m p o rary cum uli, each in violent, seem ingly e rra tic m otion, w ith open spaces betw een th em (Fig. 5). I t is in th e crest-cloud zone th a t th e m ain n o n a d ia b a tic elem ents of th e chinook are in tro d u ced . H ere th e air, d y n am ically cooled by its a sce n t of th e low er w indw ard slopes, becom es o v e rsa tu ra te d an d d ro p s enough of its m o istu re to bring th e c o n te n t to or below s a tu r a ­ tion. M o st of th e h e a t of v ap o rizatio n freed b y th e co n d en satio n is ta k en by th e air, an d m ore h e a t is acq u ired if th e w a te r d ro p lets freeze an d becom e snow or hail. U nder norm al conditions m o st of th e p rec ip ­ ita tio n falls as fine, pow dery snow on th e w indw ard side of th e range, w here th e w ind piles it in to th e canyons. A sm all fractio n of th e p re­ cip ita tio n , how ever, is carried over th e crest of th e range an d eith er su b lim ated in tra n s it or d ro p p ed in to sheltered valleys n o t reached by th e full force of th e w ind. T h is is an im p o rta n t fac to r in th e a lim e n ta ­ tion of th e sm all glaciers in th is p a r t of th e R ocky M o u n ta in region. C h a r a c t e r is t ic s

of

the

L eew ard

A ir

L eew ard of th e crest of th e range, often for m a n y miles, a chinook is a w arm , d ry w ind, w hich rem oves n ea rly all th e u n sh eltered snow from th e m o u n ta in s an d a d ja c e n t plains an d som etim es also strip s aw ay th e surface ice on lakes an d th e ice in th e soil to a d ep th of several inches. D uring th e early stages of a chinook, while surface snow is being su blim ated, th e ab so lu te h u m id ity of th e m oving air rises stead ily , as in F igure 2, w here sublim atio n of snow to w indw ard of th e sta tio n occurred th ro u g h th e range A of th e curve. D u rin g th is in terv al surface te m p e ra tu re s in th e m o u n ta in s a re extrem ely low, o ften going below -4 0 ° F. an d som etim es descending to a b o u t —8o°. T h e zone of extrem ely low te m p e ra tu re s is v ery th in , a rise of ro° som etim es occurring betw een the snow surface and 15 feet ab o v e it. T h e air on a high pinnacle, several h u n d red feet above a snow surface u n d e r­ going sub lim atio n , is sensibly, an d often m an y degrees, w arm er th a n th a t a t the snow surface. T h is p ro b ab ly explains why m o u n ta in e ers “ ca u g h t o u t ” in a chinook som etim es suffer h o rrib ly frozen feet,

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th o u g h th e ir faces are n o t even nipped b y th e cold.5 W hile su b lim a ­ tion is going on, snow cry sta ls are to rn free from th e surface a n d w hipped in to th e air, w here th e y vanish a fte r a few h u n d red feet of trav el. D u rin g the la te r stages of a chinook, w hen th e re is v ery little snow left for sublim ation, th e ab so lu te h u m id ity of th e m oving a ir low ers ra th e r rapidly, as is show n in range B of th e a b s o lu te -h u m id ity curve of F igure 2. As th e w indstorm progresses, th e b eh a v io r of th e leew ard air becom es m ore an d m ore n early like th a t p red ic ted from p u rely a d ia b a tic calculations. J u s t before th e sto rm “ blow s itself o u t , ” how ever, th e force of th e w ind decreases, an d local a ir circu latio n s begin again, producing a “ b u m p in e ss” in all th e in s tru m e n t curves. I t should be obvious from th e m echanics ju s t o u tlin ed th a t th e “ b r e a k ” in th e a b so lu te -h u m id ity curve should occur la te r in th e life of a chinook a t a sta tio n fa rth e r from th e m o u n tain s. Field o b se rv a­ tions, som ew hat in a d e q u a te because of th e w ide spacin g of in s tru m e n t sta tio n s in th is area, give q u a lita tiv e su p p o rt to th is conclusion. U p p e r -A ir D a t a

O ccurrences in th e up p er air d u rin g a chinook are n o t well know n, an d inferences from av ailab le d a ta are n o t en tirely satisfac to ry . F rom a b o u t 3000 feet above th e plains (ab o u t 8000 feet ab o v e sea level) to a b o u t 16,000 feet above sea level, to leew ard of th e F ro n t R an g e, a zone of large, billow y cum uli is u sually p rese n t d u rin g a chinook. T h is zone is roughly w edge-shaped, w ith th e apex ju s t leew ard of th e crest of th e range an d th e base far to leew ard, p ro b ab ly som ew here over th e K an sas plains. A ccording to a v ia to rs ’ re p o rts th e zone is largely w indless and is in te rm ed ia te in te m p e ra tu re betw een th e ra p id ly m oving surface air and th e air of th e “ tra d e w in d ” stra tu m . A n in te restin g check on these rep o rts is supplied b y th e sim u lta ­ neous occurrence, a t tim es, of a lu n a r halo a n d a corona. A ccording to c u rre n t theories, this can hap p en only w hen b o th a s tra tu m of su spended ice cry stals and one of w ate r d ro p lets are p rese n t in th e air. T h e ice cry stals produce the halo; th e w ate r d ro p lets cause th e corona. T h e layer of ice cry sta ls could be produced by chilling of th e air of th e cum ulus zone a t its border of c o n ta c t w ith th e colder “ tra d e w ind ” a i r ; th e layer of w ater dro p lets w ould m ost logically be p ro d u ced b y chilling of th e surface air a t its b o rd er of c o n ta c t w ith th e air of th e cu m u lu s zone. O th er ch ro m atic effects, so fain tly lum in o u s th a t a c c u ra te o b serv atio n of them is im possible, usually ac com p an y th e corona-halo 6 T h e e n tir e s u b je c t of fre e z in g a n d fro s tb ite , p a rtic u la rly a t h ig h a ltitu d e s , n e e d s a re in v e s tig a tio n . A p p a r e n tly , m o st m ed ic a l w o rk s a re b a s e d o n th e e x p e rie n c e of A rc tic e x p lo re rs, w h o su ffered n o t o n ly fro m fre e z in g b u t a lso fro m s ta r v a tio n a n d e x h a u stio n . A t h ig h a ltitu d e s fre e z in g of t h t feet, njb m a t t e r how severe, w h en n o t c o m p lic a te d b y a c tu a l s ta r v a tio n o r a c u te e x h a u stio h . seld o rr/ r e s u lt^ in m o re s e rio u s in ju r y t h a n te m p o r a r y loss of to e n a ils a n d m o re la s tin g c h ilb la in s.

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d isp lay an d resem ­ b le h i g h e r - o r d e r diffraction fringes. I t s h o u ld b e r e ­ m a rk e d th a t a t n ig h t th e cum ulus zone co n tain s few clouds. T hese o b se rv a­ tions suggest th a t th e zone of chinook a c tiv ity is ra th e r th in , a b o u t 3000 feet th ic k in the F ro n t R ange area, a c o n c l u s i o n in c lo s e a g r e e m e n t w ith th a t draw n fro m c r e s t - c l o u d ob servations. 150 MILES T o w in d w a r d , o b s e r v a t i o n s of c h in o o k a c t i v i t y a re b o th m ore dif­ ficult an d sc an tier; —-----b u t here also the F ig . 6 — S u b lim a tio n oi p la in s sn o w b y a c h in o o k . T h is v iew , ta k e n av ailab le evidence fro m a fo o th ills p e a k , sh o w s th e b a re n e s s of th e g ro u n d for a d is ta n c e suggests th a t th e of 18 m iles fro m th e c a m e ra , a s a resu lt of c h in o o k s u b lim a tio n . F ro m th e ed g e of th e b a re z o n e to th e h o riz o n . 150 m iles fro m th e c a m e ra , zone of m oving air n o rm a l sn o w c o v e r is p re s e n t. N o te a lso th e " s t a n d i n g ” c lo u d s, a n d d o e s n o t e x te n d th e s m a ll p a tc h e s of sn o w p re s e n t in g ullies, w h e re it is p r o te c te d fro m th e w in d . m any th o u sa n d feet ab ove th e surface. A v iato rs' and m o u n ta in e ers’ rep o rts suggest th a t th e w ind zone is n o t m ore th a n 3500 feet thick to w indw ard an d th a t th e w ind ten d s to trav el up valleys and along o th e r ra th e r definite to pographically controlled routes. O b serv atio n s of th e d riftin g of snow on isolated peaks to w indw ard of a chino o k -p ro d u cin g m o u n ­ tain range indicate th a t these conclusions draw n trom a d m itte d ly sc an tv evidence are a t least w ithin reason. A t y p ic a l C h in o o k s : C l o u d l e s s a n d O v e r h e a d

In ad d itio n to th e typical and easily recognizable chinooks ju s t described, a n um ber of aty p ica l w inds, resem bling chinooks in some of th e ir effects, h av e been observed. T w o of these, cloudless chinooks an d overhead chinooks, are of ra th e r fre q u en t occurrence.

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A t tim es, and ra th e r fre q u en tly in ce rtain localities, w inds resem ­ bling chinooks b u t producing no crest cloud over th e w in d w ard m o u n ­ ta in range are noted . T hese, a t first co nsideratio n , seem p h y sically im possible; b u t stu d ies of w ea th er con d itio n s d u rin g them a n d of w indw ard to p o g rap h y show th a t th e y are n o t only possible, b u t even norm al, to th e areas in w hich th e y occur. W here tw o ranges of m o u n ta in s are close to g e th er, s e p a ra te d only b y a relatively narrow valley, an d are roughly n o rm al to th e w ind,

F ig . 7— S c h e m a tic d ia g ra m of a c lo u d le ss c h in o o k

a crest cloud will be form ed over th e w indw ard of th e tw o ranges, b u t th e effects of th e accom panying chinook will be felt to lee of th e lee­ w ard range. T o observers feeling th e effects of th e w ind, no crest cloud will be visible. T h is ty p e of chinook is com m on in th e v ic in ity of Lyons, Colo., w here th e w ind crosses th e M edicine Bow M o u n ta in s, form ing a crest cloud, th en ju m p s th e narro w v alley of th e u p p er C olorado R iver, crosses th e F ro n t R ange, an d descends on th e p lain s (Fig- 7)A cloudless chinook leads to an increase in p re c ip ita tio n on th e w indw ard flank of th e w indw ard range, a slig h t decrease in th e snow on th e leew ard flank of this range, som e d riftin g of snow in to th e valley betw een th e ranges, an d a g re a t loss of snow by th e leew ard ran g e ; for it n o t only sub lim ates surface snow b u t drives g re a t q u a n titie s high in to th e air, w here, a fte r p roducing p ic tu resq u e snow plum es, som e­ tim es rising as m uch as 2000 feet above th e peaks, it is su b lim ated an d carried to leew ard. D u rin g cloudless chinooks th e cu m u lu s zone, p rese n t d u rin g norm al chinooks, is d istu rb e d an d , in place of th e usual m ass of cum uli, is occupied by " s ta n d in g ” clouds (Fig. 6). D uring m any d ay s of th e m o u n ta in w in ter resid en ts of th e foothills notice a c h a racteristic crest cloud over th e m ain range, a n d te m p e ra ­ tu re s in th e lower foothills an d on th e a d ja c e n t p lain s are a b n o rm a lly high, b u t th ere is little or no wind. Field trip s into th e high co u n try d u rin g these w arm in te rv a ls d is­ close th a t th e observed crest cloud is a chinook c re st cloud, an d t h a t a t high a ltitu d e s a tru e chinook w ind is blow ing. In th e h e a rt of th e range an d on th e higher foothills th e w ind is ex actly like th a t d u rin g a n y o th e r chinook; b u t th e leew ard air, in stea d of d escending to th e

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low er foothills an d plains, blow s v io le n tly several th o u sa n d feet ab o v e th e plains. D uring o verhead chinooks te m p e ra tu re s are a b n o rm a lly high, rela tiv e h u m id ity is v ery low, a n d v io len t s ta tic d istu rb a n ce s are n o ted on open-w ire com m u n icatio n lines an d radio receivers. S tu d ies of overh ead chinooks and th e ir effects in d ic ate p lain ly th a t m uch of th e o ften -n o ted w in ter w a rm th of th e plains region im m ed iately a d ja c e n t to th e R ocky M o u n ta in s is caused b y th ese w inds, a conclusion verified b y a com parison of te m p e ra tu re s a t s ta ­ tio ns close to th e m o u n ta in s w ith those of plains sta tio n s a t th e sam e la titu d e and a ltitu d e ioo miles or m ore to th e east, w here th e effects of these w inds are n o t felt. In the F ro n t R ange area, betw een C h e y ­ enne, YVyo., and C olorado S prings, Colo., an overh ead chinook m ay be ex pected a b o u t th ree tim es a w eek from N ovem ber i to a b o u t A pril 15. E f f e c t s o f C h in o o k s : P h y s ic a l

C hinooks, w h ate v er th e ir ty p e , produce a definite increase in th e p o te n tia l runoff of strea m s h aving th e ir sources to w indw ard of th e m ain range. In th e R ocky M o u n ta in region m ost of these strea m s are trib u ta rie s of th e C olorado R iv er s y s te m ; and th is system receives m ore w ate r to a sq u are mile of w atershed th a n th e riv er sy stem s d ra in ­ ing co m parable are as on th e ea ste rn slopes of th e Rockies. C hinook sublim atio n rem oves the snow from leew ard plains an d foothills a re as rap id ly an d th u s lengthens th e grow ing season in th e plain s a re a close to th e m ountains. In ad d itio n , it causes an ea stw ard m ig ratio n of m oisture, w hich increases th e am o u n t av a ilab le for p re ­ cip ita tio n elsew here. I t also causes a definite decrease in th e p o te n tia l runoff of ea stw a rd -d ra in in g stream s. N um erous secondary clim atic effects, caused b y d riftin g , air m ix tu re over th e m o u n ta in s, h e a tin g and cooling of th e soil, an d th e in te rru p tio n of local air circulations, h av e been noted an d are u n d o u b t­ ed ly of som e im po rtan ce, b u t th e y ca n n o t be a d e q u a te ly e v a lu a ted w ith eq u ip m en t now available. T he chinooks of th e C olorado F ro n t R ange area are responsible for a n um ber of in terestin g landform s, am ong w hich are v e n tifa c ts, blow outs, a n d (in p a rt) erosional basins. N ea r th e foothills chinooks are the only violent w est w inds; and here large w estw ard-facing o u t­ crops are polished and p itte d b y w ind-blow n san d an d ice cry stals. A typical exam ple is V alm o n t B u tte , a re sis ta n t dolerite dike rising several h u n d red feet above th e general level of th e plains ab o u t five miles w est of B oulder, Colo. T y p ical v en tifacts, all polished or p itte d on th e w est side, are found th ro u g h o u t this p a r t of th e plains region. B low outs are som ew hat com m oner in th e plain s region n ear th e m o u n ta in s th a n w ould be expected from the am o u n t of rainfall an d

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th e underlying geology. In recen t years these w in d -created b asin s h ave been used as irrigation reservoirs, an d as a re s u lt m uch w ind erosion has been prev en ted . C hinook sublim ation, b y rem oving th e snow cover from leew ard areas, an d often also th e ice or m o istu re bin d in g th e topsoil, leaves these are as exposed to w ind and o th e r erosion for a g re a te r p a r t of each y ea r th a n areas beyond th e w in d ’s influence. I t seem s p ro b ab le th a t a n u m b er of th e basins on th e plains n ea r th e m o u n ta in s, such as th e D en v er Basin an d th e B oulder V alley, owe th e ir origin in p a rt (b u t only in p a rt) to chinook action. A lthough th e m echanics of blow out an d basin erosion b y chinooks h ave n o t been ad e q u a te ly stu d ied , aero d y n am ic p rin cip les suggest th a t a basin h av in g no a ir or w a te r d rain a g e c a n n o t be ex cav ated to a n y g re a t d ep th . T h e b o tto m of a deep basin w ould be aero d y n am ically “ d e a d ” a n d w ould te n d to be a zone of dep o sitio n ra th e r th a n of erosion. If, how ever, th e depression h ad an o u tle t, aq u eo u s erosion w ould rem ove m uch or all of th e w ind-deposited m a te ria l, an d w ind erosion w ould te n d to enlarge th e o u tle t. H ence a “ b lin d ” b asin is d efinitely lim ited in size, w hereas one h av in g d rain a g e is n o t. E c o n o m ic a n d P s y c h o l o g ic a l E f f e c t s

T h e m ost fertile regions of th e H igh P lain s lie alm o st en tirely w ithin th e are a affected by chinooks an d owe a t le ast a p a r t of th e ir p ro d u c tiv ity to th e relativ ely long grow ing season p ro d u ced b y chi­ nook sublim ation. T h is is p a rtly offset b y th e red u c tio n in w ater su p p ly caused b y these sam e w inds. In a n u m b er of areas, n o ta b ly S ou th P a rk , C olo., w in te r grazing is m ade possible b y th e sublim atio n of th e snow cover b y th e chinooks. T h e to u rist a n d w in te r-sp o rts in d u strie s are a d v e rsely affected by these w inds, since th e y rem ove snow from m o st of th e easily accessible ea ste rn slopes and deposit “ good skiing sn o w ” on th e h ard -to -re ach w estern slopes. R unoff from these w estern slopes, m uch of w hich goes in to filled lakes occupying th e m elting basin s of th e P leistocene valley glaciers of th e region, m akes h ay p ro d u ctio n h ig h ly p ro fitab le in m an y areas “ over th e r a n g e ” d esp ite th e sh o rtn ess of th e grow ing season caused by high a ltitu d e . C hinooks produce definite an d obvious psychological effects on residents of th e plains and foothills are as; b u t th ese effects are n o t so pronounced as it is som etim es believed. T h e re is a com m on ten d en cy in these regions to a ttr ib u te an y u n p le a sa n t occurrence, be it an o u tb u rs t of tem per, a b ad “ h a n g -o v e r,” or an u p se t sto m ach , to th e wind. S tudies of th e relation of d etec ted crim e to w ind violence show a ra th e r definite correlation of w ind violence an d “ crim es of d iso rd er ”

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such as barro o m fights, fam ily q u arrels, a n d d ru n k en n ess. C rim es requiring careful planning, such as forgery, b u rg lary , an d em b ezzle­ m en t, seem to decrease v ery slightly d u rin g violen t w in d s.6 C o rrela­ tion of w ind violence an d these “ crim es of d is o rd e r,” p a rtic u la rly d ru n k en n ess, is n o t easy ; for a n u m b e r of in d irect com plicating facto rs a re p resen t, such as the d isc o n tin u a n ce of o u td o o r w ork d u rin g w indy w ea th er an d th e length of tim e betw een p a y d a y an d th e o n set of th e w ind. Also, as th e occurrence of a chinook leads to th e opening of snow bound m o u n ­ ta in roads, th e re is a general tow nw ard m ovem ent of the ru ral population a t th a t tim e, a tren d leading to an in ­ crease in business, an d also in m inor F ig . 8— F o r m a tio n of c o n v e c tio n a l c re s t c lo u d s crim es. J u s t before and d u rin g a chinook of any ty p e, resid en ts of th e affected areas show definite signs of nervous tension, are sh o rttem p ered , ab n o rm a lly alert, and restless, and ten d to w alk an d d riv e faste r th a n usual. T ea ch e rs re p o rt th a t a t th is tim e th e ir pupils a re restless, in a tte n tiv e , and u n ru ly ; physician s an d p h arm a cists receive increased req u ests for se d ativ es; and b ark eep ers notice an increased sale of h ard liquor. M an y persons re p o rt th a t ju s t before th e onset of a chinook th e y are unable to sle e p ; an d some co n siste n tly a c c u ra te chinook p red ictio n s h ave been m ade on th is basis. T h is “ pre-chinook in so m n ia ” closely resem bles th e sleeplessness occurring am ong unacclim ated m o u n ta in ­ eers a t v ery high altitu d e s. C o n v e c tio n a l C rest C lo u d s7

In the C olorado F ro n t R ange area, an d in m any o th e r p a rts of th e R ocky M o u n ta in region, d u rin g th e sum m er season, convectional crest clouds form early in the m orning of each norm al d ay , thicken as th e d a y advances, an d usually spread o u t over th e foothills an d in term o n tan e basins, form ing a regional cloud cover, from w hich fall n um erous local aftern o o n show ers (Figs. g and io ). I t is n o t uncom m on to find a m ajo r convectional system an d a n u m b er of m inor sy stem s in nearly in d e p e n d e n t o p eratio n in the sam e region.8 6 E . G . D e x te r: W e a th e r In flu e n ce s, N e w Y o rk a n d L o n d o n , 1004, p p . 7 9 -8 0 . 1 5 2 -1 5 3 . a n d 157. 7 T h e p h o to g ra p h s a n d m a n y o f th e o b s e rv a tio n s in c lu d e d in th is se c tio n w ere m a d e d u rin g th e p ro g re ss of re s e a rc h fin a n c e d b y a g r a n t fro m th e P e n ro se F u n d of th e A m e ric a n P h ilo so p h ic a l S o c iety . 8 Ives. W e a th e r P h e n o m e n a of th e C o lo ra d o R o c k ie s, p p . 720. 7 2 4 -7 2 6 , a n d 728—720.

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M e c h a n ic s o f M o u n t a in C o n v e c t io n s

M o u n ta in convections follow th e sam e physical law s as flatlan d convections b u t differ from them in visible effects because of th e influence of to p o g ra p h y .9 T h e in itial clouds of th e d aily co nvection cycle ten d to form in definite locations, p a rtic u la rly a t or n ea r valley h eads and over th e su m m its of peak s an d ridges. H e a tin g of slopes leads to th e estab lish m e n t of “ ch im ney c u r r e n ts ’’ an d “ convection s h e e ts ” n ea r th e ir surfaces. C ooling of th is rising a ir ev e n tu a lly produces clouds ap p ro x im ate ly abo v e th e source of th e air, as is show n d ia g ra m m a tic ally in F igure 8. T h e v ertical d istan c e betw een th e source of th e m oisture an d th e crest cloud m ay v a ry w ith in wide lim its an d depends on th e th e rm al g ra d ie n t of th e atm o sp h e re an d th e relativ e h u m id ity of th e rising air. A th e o re tic a l discussion of m o u n ta in convections h as been p ublished b y H u m p h re y s;10 a n d w here co nditions in th e m o u n ta in s ap p ro a ch tho se assum ed b y him , ac tu a l cloud beh av io r closely ap p ro x im ate s th a t suggested b y th eo ry . In a few cases, p artic u la rly w here a long valley leads u p w ard in to th e range from a poorly w ate red low land area, th e conv ectio n al u p d ra ft is so d ry th a t it n o t only does n o t form a crest cloud b u t literally “ e a ts h o le s” in clouds a lre a d y p re se n t,11 p ro d u cin g s ta tio n a ry “ w in d o w s” in a norm ally m obile cloud m ass. T h is co n d itio n is p a rtic u la rly com m on on th e ea ste rn slope of th e C olorado F ro n t R ange, a t th e heads of valleys leading in to th e S angre de C risto an d San Ju a n M o u n ta in s from th e San L uis V alley, a n d in p a r ts of th e C alifornia S ierras bordering th e O w ens V alley. A n u m b er of o th e r cloud form s, n o ta b ly b a n n e r clo u d s12 an d cloud p lum es,13 orig in ate in th e sam e m a n n er as conv ectio n al crest clouds an d are norm al phenom ena in ce rtain ra th e r sm all are as, u su ally of less th a n 25 sq u a re miles. T h e cloud plum es rising from th e C hasm on th e east face of Longs P eak, Colo., are p erh a p s th e b e s t know n. V a l u e in L o c a l W e a t h e r P r e d ic t io n

V ariatio n s in th e a m o u n t of w a te r av a ilab le for e v a p o ra tio n , in effective insolation, an d in th e th e rm al g ra d ie n t of th e a tm o sp h e re all cause changes in th e daily convection cycle of a n y area. In th e C olorado F ro n t R ange are a th e re is little d aily change in e ith e r th e a m o u n t of w ate r available for ev a p o ratio n or th e effective early m orning insolation. H ence v a ria tio n s in th e local d aily co nvection cycle can be a ttrib u te d alm o st en tirely to chan g es in th e th e rm a l g rad ie n t of th e atm osphere. 9 H u m p h re y s , op. cil.. p p . 1 0 5 -1 0 8 a n d 1 1 0 -1 1 8 ; Iv es. W e a th e r P h e n o m e n a of th e C o lo ra d o R o c k ­ ies, p p . 737 - 740 10 H u m p h re y s , op. cil., p . 117. 11 R . L. Iv e s: V a lle y -H e a d C lo u d W in d o w s, M o n th ly W eather R ev., Vol. 67, 1939, p p . n - 1 2 12 H u m p h re y s , op. cil., p p . 300 a n d 301. 13 Iv e s W e a th e r P h e n o m e n a of t h e C o lo ra d o R o c k ie s, p p . 740-742.,

F ig .

io

F ig . 9 —- N o rm a l 111id m o rn in g c re s t c lo u d s o v e r th e C o lo ra d o F ro n t R a n g e d u r in g t lie s u m m e r seaso n . F ig . 10— T y p ic a l m id d a y c o n v e n tio n a l c lo u d c o v e r o v e r M id d le P a r k . C o lo rad o , a n e ro s io n a lly m odified s tr u c tu r a l b a s in b e tw e e n th e N e v e r S u m m e r (le ft) a n d F ro n t (rig h t) R a n g e s. T h e h e a d ­ w a te rs of th e C o lo ra d o R iv e r a re in t h e n o tc h in t h e c e n te r h o riz o n .

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F ig . i i — ‘‘S h e lf ” c lo u d s h a n g in g o n th e e a s t f la n k of t h e N e v e r S u m m e r R a n g e , p h o to g ra p h e d fro m P h a n to m V a lle y , a t t h e h e a d o f t h e C o lo ra d o R iv e r. T h e s e c lo u d s, s h ro u d in g th e h ig h e r p a r t s o f th e ra n g e , a r e c h a ra c te r is tic o f m id m o rn in g in e a rly fall.

D uring a norm al sum m er d a y th e convection cycle goes through th e follow ing phases: S u n r i s e ....................................................... R a d ia tio n fog. E a rly m o r n i n g ........................................ C lear. M i d m o r n i n g ............................................. S c a tter e d c u m u li, lo c a liz ed o v er v a lle y head s a nd rid g es, a s in F ig u re 9. N o o n ............................................................ R e g io n a l clo u d co v er p resen t, a s in F igu re 10. M id a f t e r n o o n .............................................L ocal a nd reg io n a l sh o w ers. L a te a f t e r n o o n ........................................ C learing. E v e n i n g ....................................................... V e ry clear.

In la te spring and ea rly fall th is cycle m ay be so m e w h at erratic, even in th e absence of m ark ed “ o u ts id e ” d istu rb a n c e s. In early spring, late fall, an d w in te r th e d aily convection cycle is in h ib ited by lack of ev ap o rab le m oisture and decreased insolatio n . D uring y ears w hen th e regional w ater su p p ly — largely m e ltw ater from h ig h -a ltitu d e snow banks and glaciers— is n o rm al or n ea rly so, a n y m ark ed change in the daily convection cycle in d ic ates a d is tu rb ­ ance of e x tra m o n ta n e origin. W hen th e daily convection cycle begins earlier th a n usual, w hen th e clouds are ab n o rm a lly dense or ab n o rm a lly low, chilling of the air several th o u sa n d feet above th e valley floors is in d icated . T h is condition justifies a p rediction of local bad w eath er, sug g ests a falling

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b a ro m e te r, an d , if w idespread, in d icates th e passage of a cyclone over th e m o u n ta in region. A bsence of th e daily convection clouds or laten ess in th e ir a p p e a r­ ance occurs w hen th e air several th o u sa n d feet ab o v e th e surface is w arm er th a n usual. W hen th e th erm al g ra d ie n t of th e atm o sp h ere, for th e first five th o u sa n d feet or so above the surface, is “ f la tte r ” th a n usual, m oist air m u st rise to a g re a te r height before condensation ta k e s place. As air above 16,000 feet in th e F ro n t R ange area is n o rm ally in rap id ea stw ard m otion, m oist air rising to th a t a ltitu d e is d ilu ted a n d rap id ly carried aw ay by th e “ tra d e w in d s .” H ence, w hen condensation does n o t ta k e place below th is “ tra d e w in d ” stra tu m , local convections are “ o p e n -c irc u ite d .” In th e so u th e rn R ocky M o u n ta in s re ta rd a tio n or elim in atio n of th e daily convection cycle occurs du rin g periods of ab n o rm a lly high b a ro m e te r; an d w hen the clouds fail to form a t th e usual tim e, a p eriod of e x tra clear w ea th er can be pred icted w ith confidence. If th e usual aftern o o n show ers “ m is s” over a w ide area, th e passage of an anticyclone over th e m o u n tain region is in d icated . T o ta k e a specific exam ple, should th e convectional clouds over th e C olorado F ro n t R ange, durin g th e afternoon of a sum m er d ay , a p p e a r as in F igure 9, a p rediction of ab n o rm a lly clear w eath er for th e following d ay w ould be justified. W idespread d ro u g h t, usually due to in a d e q u a te w in ter snow fall, te n d s to re ta rd th e form ation of convectional crest clouds in a m an n er sim ilar to th a t of a period of high b aro m e ter and will o p era te d u rin g a large p a r t of th e d ry sum m er in stea d of “ once every eig h t d a y s .” D uring th e ea rly fall, w hen general air te m p e ra tu re s are close to th e freezing p o in t b u t a ir n ea r th e surface is fairly w arm d u rin g m uch of th e d ay , “ shelf ” clouds form along th e sides of m an y ridges (Fig. 11). T h e form atio n of th is special ty p e of convectional crest cloud is caused b y th e presence of d rifts of cold air from the highlands, w hich occupy th e centers of th e v alleys and in h ib it th e form atio n of a regional convectional cloud cover. In general, th e first ap p earan ce of these shelf clouds coincides w ith th e beginning of a period d u rin g w hich d aily early-m orning ste am fogs are p re se n t14 in m an y of th e m ain v alleys of th e region; and these occurrences are a b e tte r in d icatio n of th e end of th e m o u n tain sum m er th a n th e calend ar. A t first consideration th e convectional crest clouds seem to be of little im p o rtan ce to h u m a n ac tiv itie s. T o m any people they are e ith e r sim ply p ic tu resq u e or a nuisance, causing cloudy aftern o o n s. A ctually, th e ir effects are im p o rta n t, inasm uch as m an y ac tiv itie s in th e m o u n ta in region, such as to u rist trip s and haying, m u st be begun long before sunrise, so th a t th e y can be finished before th e daily' a f te r ­ 14 R . L. Iv e s : “ R iv e r F o g s " of M id d le P a rk , C o lo rad o , B u ll. A tn e r. M eteovol. Soc., Vol. 20, 1939,

pp. 415-417.

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noon show ers com e. As a resu lt of th e d aily co n v ectio n cycle, th e m o u n ta in guide an d th e ran c h er rise w ith th e false daw n , w o rk u ntil early afte rn o o n , an d re st u n til ea rly evening. T h e su m m er ‘eig h to ’clock b e d tim e ” of th e m o u n ta in people is n o t a ru ra l v a g a ry b u t an econom ic necessity. MILES LONG

"TRADE WINDS"

F i g . 1 2 — W e s t- e a s t c ro ss s e c tio n of t h e C o lo ra d o F r o n t R a n g e , sh o w in g c o n d i­ tio n s d u r in g t h e life o f a C h e y e n n e -d r ift c re s t c lo u d .

C h e y e n n e -D r ift C rest C lo u d s

B etw een th e M ississippi V alley a n d th e R o c k y M o u n ta in s th e p lains slope u p w ard , rising a b o u t 5000 feet in a b o u t 750 m iles. P lains air, h ea te d b y th e sun, te n d s to d rift upslope as it ex p an d s. U nder o rd in a ry conditions th e upslope d rift is b ro k en u p b y th e m uch m ore pow erful local v ertical convections, so t h a t th e d rift, ex c ep t in certain ex trem ely fav o rab le v alley system s, is of little im p o rta n ce . U n d er exceptional conditions, how ever, a d efin ite upslope d rift occurs an d produces clouds all along th e R o ck y M o u n ta in fro n t, w here th e a ir m otion is co n v erted from n e a rly h o rizo n tal in to n early v ertical b y th e to p o g rap h y . In su m m er, w hen th e th e rm a l g rad ie n t of th e atm o sp h e re over th e plains is rela tiv e ly “ s te e p ” a n d p lain s air is n ea rly sa tu ra te d w hen it reaches th e m o u n ta in fro n t, clouds form a t or n ea r th e surface, prod u cin g fogs locally kn o w n as “ C heyenne fogs. ” 15 T h e air d rift producing th e m could well be called a “ C heyenne d rift. ” In w in ter, w hen th e th e rm al g ra d ie n t of th e a tm o sp h e re o v er th e p lains is relativ ely “ f la t” an d th e a ir d riftin g upslope across th e p lain s is relativ ely u n s a tu ra te d w hen it reaches th e m o u n ta in fro n t, th e clouds R . G . S to n e : F o g in t h e U n ite d S ta te s a n d A d ja c e n t R e g io n s. Geogr. Rev., V o l. 26, 1936 p p . r e fe re n c e o n p . 1 3 0 ; H . R . B y e rs : S y n o p tic a n d A e r o n a u tic a l M e te o ro lo g y , N e w Y o r k 'a n d L o n d o n , 1 9 3 7 . P P . I P S a n d 2 0 9 -2 1 0 . H I-1 3 4 ,

FRONT

RANGE

CREST

CLOUDS

41

p ro d u ced b y co n d e n sa tio n of th e m o istu re carried b y th e C h eyenne d rift a re form ed a t g re a te r a ltitu d e s, usually a t or n e a r th e crest of th e range. W hen , as is u sually th e case, cond en satio n ta k es place n e a r or w ith in th e “ tra d e w in d ” stra tu m , te n u o u s stre a m e rs of cloud are carried m a n y m iles to th e east. M e c h a n ic s o f C l o u d P r o d u c t io n

M o st sum m er C heyenne fogs are ty p ical ad v ectio n fogs an d h ave been ad e q u a te ly described an d ex p lain ed .,(i As th e a ir m oves upslope, it is cooled a d ia b a tic a lly by expansion an d m ay also lose som e h ea t by rad ia tio n . E v en tu ally , if the d rift is n o t in te rru p te d , th e air is cooled sufficiently so th a t condensation, leading to fog or cloud fo rm atio n , ta k es place. C h e y en n e -d rift crest clouds are w in te r eq u iv ale n ts of C heyenne fogs an d w ould closely resem ble th em , except for th e a ltitu d e a t which th e y norm ally occur, w ere it n o t for th e presence of th e “ tra d e w in d s” n o t far above th e crest of th e m ain range. T h e co n d itio n s d u rin g the p ro d u ctio n of a C h ey en n e-d rift crest cloud an d its accom panying strea m e rs are show n in F igure 12. T h is cloud m u st be co n tin u ally reg en erated by new accretio n s of m oist air, or th e stream ers, and finally th e crest cloud, will be dissip ated . A lthough th e facto rs leading to th e p ro d u ctio n of b o th C heyenne fogs an d C h ey en n e-d rift crest clouds are know n, th o se leading to th e p ro d u ctio n of th e d rift itself are n o t well understo o d . As a resu lt, pred ictio n s of C heyenne d rifts an d th e ir accom p an y in g clouds ca n n o t be m ade w ith an y assurance. P re se n t d a ta suggest th a t a b aro m e tric high over th e M ississippi V alley and norm al or low b aro m e tric pressure a t th e m o u n ta in fro n t will som etim es stim u la te th e upslope d rift and lead to cloud or fog form atio n a t or near th e m o u n ta in fro n t. O cca­ sionally, ab n o rm a l h u m id ity in th e M ississippi V alley has im m ed iatelv preceded th e ap p e aran c e of C heyenne fogs. T h e ra th e r in a d eq u a te o b serv atio n al d a ta a t p rese n t av ailab le suggest th a t th e C heyenne d rift is alw ays p resen t b u t th a t only u n d er ra th e r exceptional co n d itio n s is it stro n g enough to overcom e n um erous opposing forces and produce fogs or crest clouds. T h e only im p o rta n t effect of the C heyenne d rift in th e m o u n tain region is th e poor visib ility produced d u rin g th e life of th e fog or crest cloud. T h is is im p o rta n t to a v ia to rs b u t has little effect on m o u n tain activ ities. C o ld -F r o n t C rest C lou d s

W hen a m ass of cold a ir inv ad es a w arm er region, the m o istu re in th e w arm er air is likely to be condensed, p rodu cin g a mass of clouds 16 See, for e x a m p le , H u m p h re y s , op. cit., p. 2 74; B y e is, op. cit., p p . 2 0 0 -2 1 0 ; an d S to n e , op. cil., p p . 120—12 1.

42

THE

GEOGRAPHICAL

REVIEW

in th e c o n ta c t zone. W hen th is m ig ra to ry c o n ta c t zone, or fro n t, passes over a region of rugged to p o g rap h y , h av in g v ario u s local and pow erful air circulations, its progress is likely to be in te rru p te d a n d its sh ape te m p o rarily m odified. T h is is usu ally tru e w hen a cold fro n t com es very n ea r to th e R ocky M o u n ta in s. W in te r sto rm s, in p a rtic u ­ lar, a re often “ hung u p ” over th e ranges for periods of a few h o u rs to several days. D u rin g th e period of d elay th e c o n ta c t zone, filled w ith clouds, form s a v ery dense cre st cloud o v er th e su m m it of th e range. T h e passage of a ty p ic al cold fro n t across th e C olo rad o F ro n t R an g e a t a b o u t 40° N . is show n in F ig u re 13.

; F ig . 13— W e s t to e a s t c ro ss se c tio n of t h e C o lo ra d o F r o n t R a n g e a re a , s h o w in g t h e p ro g re ss of a ty p ic a l c o ld -fro n t s to r m a c ro s s t h e ran g e .

M e c h a n ic s o f a C o l d F r o n t

As a cold fro n t ap p ro a ch es a m o u n ta in ran g e a n d su rm o u n ts it, th e in v ad in g cold a ir is fu rth e r cooled by expansion, w hich m a y lead to co n d en satio n w ith in it, an d its m otion is re ta rd e d n o t o nly b y the change of direction of m otion b u t b y local air cu rren ts, such as the usual valley convections an d th e C heyenne d rift. A lthough th e in v ad in g cold a ir te n d s to be d en ser th a n th e air alre ad y p rese n t in th e region, it does n o t im m ed ia te ly se ttle to th e lee­ w ard surface of th e range b u t d rifts along a t som e d ista n c e ab o v e the surface for som e miles, w hile th e local, an d often opposing, a ir d rifts co n tin u e n ear th e surface. T h is is som etim es ra th e r d ra m a tic a lly evidenced b y th e “ in s ta n ta n e o u s ” ap p e a ra n c e of to w erin g g ia n t cum uli over valley heads and in o th e r locations w here “ a ir f o u n ta in s ” are p rev a len t. T hese are produced w hen th e local air (w arm ) rises up w ard an d p e n e tra te s th e cold zone overhead. C onditions over th e m ain range d u rin g th e early p h ase of a coldfro n t sto rm (11 :oo in Fig. 13) are show n in F igu re 14. T h e p eak s on th e divide are shrouded in sw irling snow. T h e to p of th e c o n ta c t zone, as d eterm in e d by tria n g u la tio n , is a b o u t 17,000 feet ab o v e sea level. I t will be n oted th a t th e sm oke is blow ing roughly to w ard th e cam era an d th a t th e storm is m oving in th e sam e direction.

F ig .

15

F ig . 14— V iew of a c o ld -fro n t c re s t c lo u d o v e r t h e C o lo ra d o F ro n t R a n g e d u rin g a n e a rly s ta g e of a c o ld -fro n t s to r m (1 1 :0 0 in F ig . 13). A b liz z a rd is ra g in g a ro u n d th e m o st d i s t a n t p e a k s v isib le in th is p ic tu r e , th e A ra p a h o s , a b o u t 8000 feet a b o v e th e p h o to g ra p h ic s ta tio n a n d 26 m iles w est of it. F ig . 15— A la te r p h a s e of a c o ld -fro n t s to rm (2 :0 0 in F ig . 13). H e re th e f ro n t h a s “ s h e lv e d o u t " o v e r th e p lain s, th e m a jo r s u rfa c e w in d h a s v e e re d , a n d th e m o u n ta in s a re c o m p le te ly b u rie d in c lo u d s, w h o se lo w e r su rfa c e is less t h a n 2000 feet a b o v e th e p lain s.

43

44

THE

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REVIEW

A la te r phase of a cold -fro n t sto rm , w hen th e cloud b a n k has “ shelved o u t ” over th e plains (2:00 in Fig. 13), is show n in F ig u re 15. T h e storm is still m oving roughly from w est to ea st, b u t th e w inds ju s t above the surface are com ing from th e n o rth , an d th e surface-air d rift d irec tly opposes th e storm m otion. T h is is a com m on con d itio n d u rin g la ter phases of a co ld -fro n t storm . S to rm s of th is ty p e are com m o n est in w inter. T h e y are p roducers of snow in four different w ays: 1. By a d ia b a tic cooling of th e in v ad in g a ir m ass as it rises to cross th e range. T h is effect is m inor an d localized. 2. By cond en satio n of m o istu re carried u p w ard in to th e invading cold a ir by “ chim ney c u r r e n ts ” in w estern-slope valleys. T h is is th e cause of som e of th e “ u n b e lie v a b ly ” h ea v y snow falls in certain areas. 3. By co ndensation of m o istu re carried u p w ard b y “ chim ney c u r r e n ts ” a n d “ convection s h e e ts ” on th e ea ste rn slope of th e m ain ran ge. T h is effect is m inor an d localized. 4. B y cond en satio n of m o istu re a t th e sto rm fro n t. T h is is the chief cause of p re c ip ita tio n in this area. A ccording to th e air-m ass h y pothesis, th e m o istu re p re c ip ita te d d u rin g th e w in te r in th e R ocky M o u n ta in region has a G ulf of M exico source. P r e d ic t io n a n d E f f e c t s

C o ld -fro n t sto rm s are b est p red ic ted from a s tu d y of co untry-w ide w ea th er conditions, ra th e r th a n from a s tu d y of local clouds. W eath er p red ictio n s issued by th e U nited S ta te s W e a th e r B u reau an d those p rep a re d by th e v ario u s air lines for th e ir own use h av e p roved of a fair accu racy in regard to th e a p p ro x im a te tim e of a rriv a l of a coldfro n t storm in this region. T h e chief effect of co ld-front sto rm s is to su p p ly th e m o u n tain region an d a d ja c e n t plains w ith m oisture. As these sto rm s are largely w in te r phenom ena, m ost of th e m o istu re falls as snow , w hich is stored a t high a ltitu d e s until sum m er, w hen it m elts, an d th e re b y m ain tain s stream flow th ro u g h o u t th e year. As cold-front sto rm s are p red ic tab le m a n y hours, even several d ays, in ad v an ce, w ith a reasonably good a n d c o n s ta n tly im proving “ b a ttin g a v e ra g e ,” th e inconvenience to h u m a n a c tiv itie s caused by th em is m uch less th a n th a t caused b y th e less v io len t, b u t less accu ­ ra te ly p red ictab le, local storm s. Increased use of th e fo recastin g services alre ad y available will g re a tly reduce th e tra n s p o rta tio n delavs an d o th e r tro u b les caused by these storm s. M ixed T ypes A n u m b e r of th e crest clouds observed each y ear o ver th e m ain range ca n n o t be a ttr ib u te d to a n y single ca u sa tiv e force. T h ese are

FRONT RANGE CREST CLOUDS

45

th e ’’mixed ty p e s ," o fte n very d i f f i c u l t to e x p la in , n e a rly u n p re d ic ta b le , and e r r a t i c in t h e i r b eh av io r. F ie ld o b serv atio n s s tro n g ly suggest th a t the fo rc e s causing th e vario u s a i r d r i f t s which produce th e s e v e ra l c re s t-c lo u d -types a re c o n sta n tly opera­ tiv e b u t th a t t h e i r e f f e c ts u su a lly "ca n c el o u t." When a s in g le fo rc e becomes dominant, a "pure type" o f c r e s t cloud i s produced. When two fo rc e s become stro n g sim ultaneously and do n o t e n tir e ly oppose each o th e r, a "mixed type" of c r e s t cloud may be formed. A complete stu d y of th e se "mixed types" would be a t r e a t i s e on th e th eo ry of perm utations and combi­ n a tio n s as a p p lie d to lo c a l meteorology and, as few o f the v a rio u s com binations re c u r w ith any r e g u la r i­ t y , would be o f academ ic, r a th e r than p r a c t ic a l, in ­ te re s t. I t i s e n tir e ly p o ssib le th a t most o f th e lo c a l p re d ic tio n f a ilu r e s a re caused by assuming th a t a c r e s t cloud o f "mixed type" i s a "pure ty p e ," an a s ­ sumption th a t e lim in a te s from c o n sid e ra tio n a l l b u t th e main cloud-producing a i r m otions.

G

e o g r a p h ic a l

R

e v ie w

P U B L IS H E D B Y

T h e A m e r ic a n G e o g r a p h ic a l S o c ie t y of

N e w York

VOL.

3R

NO.

3

19

Submitted to the Faculty of the Graduate School in partial fulfillment of the requirements for the degree, Doc­ tor of Philosophy, Department of Geography, Indiana Uni­ versity.

F R O N T IE R S

AND

S E C U R IT Y

447

is n o m o re likely than a sim ple legal solution. W e can p ro b a b ly d o b etter th a n last tim e, b u t even o u r best w ill leave p o w e r differentials b etw een in d iv id u al units, an d the p ro b le m o f te rrito ria l security w ill, th erefo re, rem ain. T h e g eo g rap h er has a greater k n o w led g e o f b oundaries an d a b e tte r u n d ersta n d in g o f buffer states, an d th e political scientist has a b etter c o m p re ­ hen sion o f th e w o rk in g o f in te rn atio n a l org an izatio n . T o g e th e r th ey should be able to fo rm u late legal provisions fo r sanctions th a t h arm o n ize w ith th e d istrib u tio n o f p o w er. T h e co n trib u tio n s o f frontiers, buffer states, an d in te rn atio n a l o rg an iz atio n to te rrito ria l security can be b etter in teg rated , b u t no treaty , even th o u g h perfect, can assure a p e rm a n e n t peace. It is n o m o re possible to d ra w a lasting m ap o f an in te rn atio n a l o rd e r th a n it is to d ra w an im m u tab le co n stitu tio n fo r th e co n d u c t o f n atio n al life. In a d y n am ic w o rld in w h ic h forces shift and ideas change, no legal stru ctu re can rem ain acceptable fo r any le n g th o f tim e. P reserving o rd er w ith in th e state is n o t a question o f designing once an d fo r all th e final an d p erm a n en t solution o f all p ro b lem s b u t a q uestion o f m ak in g daily decisions th a t w ill adjust h u m a n frictions, balance social forces, an d co m p ro m ise po litical conflicts. It involves deciding ever anew in th e lig h t o f ch an g in g circum stances w h a t should be preserved and w h a t should be changed. P re­ serving o rd er in th e in tern atio n al society is a p ro b le m o f the sam e n atu re. It d em ands all the skill an d artistry o f the political ex p ert. T h e scholar can elucidate the lessons o f histo ry , b u t o n ly th e statesm an in his d a y -to -d a y co n d u c t o f th e affairs o f nations can m ake treaties w o rk an d in tern atio n al in stitutions function.

EARLY H U M A N O C C U P A T IO N O F T H E C O L O R A D O H E A D W A T E R S R E G IO N A N A R C H E O L O G IC A L R E C O N N A IS S A N C E * Ronald L . Ives H E re c o n stru c tio n o f past c u ltu re areas,” says C a rl S au er,1 “ is a slow task o f d etective w o r k ,” th e collecting o f evidence an d th e w eav in g o f it to g e th e r. A n d , he continues, it calls fo r a reg io n al specialist; “he m u st n o t o n ly k n o w th e re g io n as it appears to d a y ; h e m u st k n o w its linea­ m en ts so w ell th a t h e can fin d in it th e traces o f th e past, an d he m u st k n o w its qualities so w ell th a t h e can see it as it w as u n d e r past situations.” In the stu d y o f an cient h u m a n cultures, th e d etective w o rk becom es alm ost as difficult as th a t n eeded to solve a “ p erfect c rim e ” an d requires th e w eighing o f ev idence in m a n y fields. T h e p ro b le m o f th e p reh isto ric h u m a n activities in th e C o lo ra d o head w aters area, h ere in to be described, is typical. T he arch eo lo g ical evidence is alm o st m eaningless u n til th e past an d present g eo g ra p h ic b a c k g ro u n d is u n d ersto o d . T h en , against th e b ac k g ro u n d o f local g eo g ra p h y , g eo lo g y , a n d m e te o ro lo g y , th e cu ltu ral rem ains can be fitte d in to a consistent an d plausible pictu re. T h e evidence here rep o rted indicates th a t f ro m th e b eg in n in g o f h u m a n o cc u p atio n o f th e area, n o t m uch m o re th a n 4000 years ago, u n til 1879, w h e n th e last o f th e U n co m p ah g re U te s w e re d e p o rte d to so u th w e stern C o lo ra d o , th e ab o rig in al inhabitants established an extensive n e tw o rk o f trails, co n n e ctin g strategic quarries, cam ps, passes, fords, an d h u n tin g grou n d s. M a n y o f these trails, because o f g eo g ra p h ic con d itio n s still existing, fo llo w ed th e ap p ro x im a te courses o f m o d e rn roads and trails. T h a t this an cient trail system ex ten d e d outside the re g io n described m a y be assum ed w ith som e confidence, d eterm in a tio n o f th e exact ro u tes aw a itin g o n ly fu rth e r field investigations.

T

* Field w o rk w as assisted b y several g ra n ts fro m th e P e n ro se F u n d o f th e A m e ric a n P hilosophical S o cie ty , b y th e U n iv e rs ity o f C o lo ra d o M u se u m , an d b y p r iv a te sources. L ib ra ry , la b o ra to ry , a n d d a rk ­ r o o m facilities w e re m a d e av a ilab le b y th e M u se u m an d b y th e D e p a r tm e n t o f G e o lo g y o f th e U n iv e rsity o f C o lo ra d o . M r. B ru c e S n o w o f B o u ld e r, C o lo ., w h o assisted in th e field o n sev eral trip s, g a v e th e w r ite r free access to his ex ten siv e co llectio n o f artifacts fr o m A ra p a h o Pass a n d su p p lie d m a n y d a ta p e r tin e n t to this s tu d y . T o M r. E a rl M o rris o f B o u ld e r, C o lo ., th e w r ite r is g ratefu l fo r h e lp fu l discu ssio n s o f th e field e v id en ce a n d its possible significance. D u r in g th e n in e field seasons d e v o te d to th e se studies, n e a rly e v e ry re sid e n t o f th e re g io n g av e so m e f o r m o f assistance— h elp th a t is h e re g ra te fu lly ac k n o w le d g e d . 1 C . O . S auer: F o re w o rd to H isto ric al G e o g ra p h y , A nnals A ssn. o f A m er. Geogrs., V o l. 31, 1941, p p . 1 -2 4 ; references o n p p . 9 a n d 10.

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o

F ig . i — D ra in a g e m a p o f area d escrib ed in th e te x t: th e s tip p led area w as n o t stu d ied . Scale a p p ro x im a te ly I : 720,000.

T he L andform s

and

T h e ir H is t o r y

T h e re g io n w ith w h ich w e are concerned is sh o w n in F igure i. T h e F ro n t R an g e o f the R ockies here (n o rth w e st o f D en v e r) rises ab ru p tly fro m the G reat Plains to serrate peaks w ith altitudes o f 13,000 an d 14,000 feet. T h e Plains are a series o f so m e w h at in terrelated erosion surfaces o n sedim ents o f P ennsylvanian to M iocene age. T h e F ro n t R ange is a co m p lex o f g ran ite, schist, an d gneiss o f early p re -C a m b ria n age w ith various m ineralizations an d intrusions o f later ages. W e st o f th e F ro n t R ange is M id d le P ark, a stru ctural an d erosional basin floored w ith in te rb ed d ed volcanics an d fresh­ w ate r lake deposits o f P aleocene an d later ages.2 A lth o u g h ev ery p rev io u s o ccurrence in an area m u st be considered in an analysis o f any phase, th e p rePleistocene h isto ry o f this reg io n is only in d irectly p ertin en t to this study. 2 T h e g en e ra liz ed g e o lo g y o f this re g io n is s h o w n o n th e U . S. G eo lo g ical S u rv e y ’s “ G eo lo g ic M ap o f C o lo r a d o ,” I : 500,000, 1935 (b y th e S u rv e y in c o o p e ra tio n w ith th e C o lo ra d o S tate G eo lo g ical S u rv e y B o a rd an d th e C o lo r a d o M eta l M in in g F u n d ).

450

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R ep o rts by m a n y investigators, b y no m eans in ag reem en t, present various app ro aches to this still unso lv ed an d h ig h ly co m p licated p ro b le m .3 T h e later h isto ry o f th e reg io n is likew ise ex tre m e ly co m p lex . R ecent studies4 h ave p ro d u c e d a n u m b e r o f sim ilar, b u t n o t co n fo rm ab le, glacial T able

i

— L a t e - P l e is t o c e n e

STAGE

M ORAINES

N ev a * M onarch C f M onarch B j M onarch A§ Arapaho

C om p ou n d Single C om p ou n d Single Single

Arapaho A j

C om p ou n d

R iverJ

Single

Stillwater

C om p ou n d

C hronology

of the

M onarch

CORRELATIO NS

“Little Ice A g e ’’ Fennoscandian Scanian -----Pomeranian M ankato Brandenburg T aze w el 1-C a ry W ar the Iow an Riss Illinoisan

V a lley YEARS P R E -1 9 0 0 4 ,0 0 0 1 0 ,4 0 0 1 3 ,4 0 0

-----2 5 ,0 0 0 3 5 ,0 0 0 6 5 ,0 0 0 T 2 5 ,0 0 0 (? )

W ald en H o llo w H ell Inlet — Pre-Stillw ater glacial debris o f undeterm ined age and origin * T h is stag e is e q u iv a le n t to th e p ro ta lu s su b stag e o f th e P o u d re V alley (B ry an an d R ay, op. cit.). D a tin g based o n F. E. M a tth e s : T h e G laciers o f O u r O w n T im e , M a za m a . V o l. 21, 1939, N o . 12, pp. 2 0 -2 6 . f E q u iv a le n t to th e L o n g D r a w su b stag e o f th e P o u d r e V alley (B ry an a n d R ay , op. cit.). X D a tin g based o n B ry a n a n d R ay , op. cit. § T h is is p ro b a b ly a f o rtu ito u s ly p re se rv e d ea rly phase o f th e M o n a rc h B stage.

ch ro n ologies. In v e ry general term s, glaciers o f th e earlier p a rt o f the Pleis­ to cen e w e re o f th e icecap ty p e, so far as can be d eterm in e d fro m th e som e­ w h a t a m b ig u o u s evidence n o w rem a in in g . L ater Pleistocene glaciations w ere m u ltip le, w ith at least fo u r m a jo r advances d u rin g th e W isconsin. A later Pleistocene ch ro n o lo g y , based o n th e sequence o f events in the M o n a rc h V alley, is given in T ab le I. T his sequence is substantially th e same 3 H . P . L itd e : E ro s io n a l C ycles in th e F ro n t R an g e o f C o lo ra d o a n d T h e ir C o rre la tio n , Bull. Geol. Soc. o f Am erica, V o l. 36. I 92 5. PP- 495 ~ $ 12> R- V H e a to n : A n cestral R o ck ies a n d M eso zo ic a n d Late P ale o zo ic S tra tig ra p h y o f R o c k y M o u n ta in R eg io n , B ull. Atner. A ssn. o f Petroleum Geologists, V ol. 17, 1933, p p . 10 9 -1 6 8 ; W . T . Lee: P en ep lain s o f th e F ro n t R a n g e a n d R o c k y M o u n ta in N a tio n a l P ark , C o lo ra d o , C . S . Geol. S u rvey Bull. y j o - A , 1922, F. JVI. V a n T u y l a n d T . S. L o v e rin g : P h y sio g ra p h ic D e v e lo p m e n t o f th e F ro n t R an g e , B ull. Geol. Soc. o f Am erica, V ol. 46, 1935, P a rt 2, p p . 1291-1 3 4 9 ; W . W . A tw o o d a n d W . W . A tw o o d , Jr.: W o r k in g H y p o th e sis fo r th e P h y sio g ra p h ic H is to ry o f th e R o ck y M o u n ta in R e g io n , ibid., V ol. 49, 1938, P a rt 1, p p . 9 5 7 -980. '•K irk B ry a n an d L. L. R ay : G eo lo g ic A n tiq u ity o f th e L in d e n m e ie r S ite in C o lo ra d o , Smithsonian M isc. C olls., V ol. 99, N o . 2, 1940; R. L. Ives: G lacial G e o lo g y o f th e M o n a rc h V alley , G ra n d C o u n ty , C o lo ra d o , Bull. Geol. Soc. o f Am erica, V o l. 49, 1938, P a rt 2, p p . 1 0 45-1 0 6 6 ; idem: [R e p o rt o f P ro g ress], A m er. Philos. Soc. Year Book 1940, P h ila d e lp h ia , 1941, p p . 195-197.

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as th a t in th e G ra n d Lake area. T h e ch ro n o lo g y , like m o st o th ers co v erin g th e sam e tim e interval, is co n stru cted o n the assum p tio n th a t th e clim atic changes leading to glaciations w ere w o rld -w id e , so th a t sim ilar sequences o f glacial events, w h e re v e r th ey are fo u n d , represen t th e sam e tim e intervals. A lth o u g h this c h ro n o lo g y seems to be the o nly reasonable one fo r the area co n cerned, it should be reg a rd e d as a “ w o rk in g d ra ft,” subject to revision w h e n m o re evidence has been collected and as vario u s disagreem ents in glacial sequences are w o rk e d out. A t th e tim e o f w ritin g (June, 1941), th e glaciations o f th e C o lo ra d o h eadw aters re g io n can be co rrelated “ stage for stage” o n ly w ith those near Estes P ark. C o rrela tio n s w ith those in th e P o u d re h ead w aters re g io n an d w ith those in the valleys trib u ta ry to B o u ld er C reek are o n ly partial, each o f these drainages h aving, acco rd in g to present evi­ dence, one stage few er th a n th e C o lo ra d o h eadw aters region. P resent- D a y

C l im a t e

W ith in th e area, clim ate ranges fro m th a t o f the G reat Plains, so m ew h at m o d ifie d b y c h in o o k w in d s,5 to v ery severe arctic-alpine, w ith w in te r co n d i­ tions resem bling those re p o rte d fro m the A ntarctic. O n th e Plains, a h u m a n g ro u p h av in g fire, clothes, an d shelter such as the tepee can live the year ro u n d w ith o n ly a few days o f intense d isco m fo rt due to subzero cold. Such w as the e n v iro n m e n t o f the Plains Indians. In the foothills, ro u g h ly b etw e en 8000 an d 11,000 feet, th e w in ters are so severe th a t any g ro u p n o t h av in g p erm a n en t hab itatio n s w o u ld suffer several m o n th s o f m isery each year, because o f th e intense cold an d deep snow . It can be assum ed w ith som e confidence th a t th e p re -C o lu m b ia n in h ab itants o f th e foothills reg io n m ig ra te d to the Plains in w in te r, as m o st o f th e n o n h ib e rn a tin g gam e anim als do today. T h e m o u n ta in reg io n , en tirely above the n ,o o o -f o o t co n to u r, is b u ried u n d er deep snow , and is practically im passable for a m a n afoot, fo r ab o u t eig h t m o n th s o f the year. D u rin g the m o u n ta in su m m er th e F ro n t R ange can be crossed, fro m tim b e r o n one side to tim b e r o n th e o th e r, in less th a n a d a y ’s w alk in favorable locations, such as A rap ah o Pass (Figs. 4 and 5). Because o f th e “ d aily ” cycle o f su m m er storm s, consisting o f rain, hail, and occasional snow , crossings m ade d u rin g th e early ho u rs o f the day are fairly easy and those m ade in th e afte rn o o n are difficult and, to say th e least, u n ­ pleasant. 5 R, L. Ives: C o lo ra d o F ro n t R an g e C re st C lo u d s an d R elated P h e n o m e n a , Cee^r. R e r., V ol. 31, 1941, p p . 2 3 -4 5 ; sec also th e b ib lio g rap h ical references.

452 .

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a n d

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A rtifacts fo u n d in this re g io n are o f a crude generalized ty p e sim ilar to those fo u n d on th e Plains an d in th e m o u n ta in s a t least as far w est as th e crest o f th e W asatch . D escriptions o f Plains artifacts an d o f th e Y u m a an d F o lso m m aterials fo u n d in various parts o f C o lo ra d o h av e been p ublish ed b y m a n y w o rk e rs.6 FrG. 2— A rtifa cts f r o m A rap a­ h o Pass. B ecause o f th e tran slu c en cy a n d v a rie g a tio n o f th e m aterials, each sp ecim en w as co a ted w ith su b lim ate d a m ­ m o n iu m c h lo rid e b e fo re p h o to ­ g ra p h in g . A , p ro je c tile p o in t, w h ite q u a rtz ite , p ro b a b ly im p o rte d f r o m th e u p p e r A rk an sas V alley; B . re c ta n g u la r scraper, “ w h ite q u a r tz ,” p ro b a b ly m a d e at the B a k e r G u lch q u a rry ; C , scraper, v a rie g a te d ja sp e r. T h is to o l a n d E , F, a n d G w e re p r o b a b ly m a d e at th e T a b le M t. q u a rry ; D , scraper, fin e -g ra in e d w h ite q u a rtz ite , p ro b a b ly m a d e f r o m a n o d u le w e a th e re d o u t o f a sed im en ta ry ro c k ; E, scrap er, b r o w n c h e rt; F, b ro k e n p ro je c tile p o in t, v a rie g a te d ja s p e r; G , c ru d e scrap er, b r o w n ch ert.

A lth o u g h th e ir studies w e re m a d e m o re o r less in d e p en d e n tly and w ere, in general, ra th e r ro u g h reconnaissances, th e investigators have, so far as pos­ sible, “ tied in ” th e ir w o rk w ith th a t carried o u t in ad jo in in g regions. T he re g io n here described overlaps th e R o c k y M o u n ta in N atio n al P ark region stu d ied by Y elm . T h e types o f artifacts fo u n d are illustrated in F igure 2. Grinding and Striking Tools. T he grinding and striking tools foun d consist o f m etates and m anos, used for grinding grain, and stone hammers; m ortars and pestles are found only at the W h ite R ock sites in the valley o f B oulder Creek, about six m iles northeast o f Boulder. N u m erou s m etates have been found in the Plains area. M ost o f them are m ade o f Dakota (Cretaceous) sandstone, but a num ber m ade o f Fountain (Pennsylvanian) or Lyons (Perm oPennsylvanian) sandstone have been found, and a few made o f local (pre-Cambrian?) quartz­ ite have been reported. N u m erou s m anos have also been found; but, as m anos were com ­ m o n ly river boulders, w ith w h ich valley floors m the m ountain region are paved, few have been recognized w est o f the foothills. 6 E. B . R e n a u d : A rc h a e o lo g ic a l S u rv e y o f E a stern C o lo ra d o , F irst R e p o rt, 1931, S eco n d R ep o rt, 1932, T h ir d R e p o rt, 1933, F o u rth R e p o rt, 1935, U n iv . o f D e n v e r, D e p t, o f A n th r o p o lo g y ; idem: P re ­ h isto ric F laked P o in ts fr o m C o lo ra d o an d N e ig h b o rin g D istric ts, Proc. Colorado M useum oj X a t. H ist., V o l. 10, N o . 2, 1931; idem: Y u m a a n d F o lso m A rtifa cts, ibid., V ol. 11, N o . 2, 1932; idem: T h e First T h o u s a n d Y u m a -F o ls o m A rtifa cts, U n iv . o f D e n v e r , D e p t, o f A n th ro p o lo g y , 1934; J . D . F ig g in s: F o lso m an d Y u m a A rtifa cts, 2 p arts, Proc. Colorado M useum o fX a t. H ist., V ol. 13, N o . 2, 1934, a n d V o l. 1 4 ,N o . 2, 1935; M . E. Y elm : A rch aeo lo g ica l S u rv e y o f R o c k y M o u n ta in N a tio n a l P a rk -E a s te rn F o o th ills D istric t (M a s te r’s T hesis, U n iv e rs ity o f D e n v e r , 1935).

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W o rn fragm ents o f Lyons (?) sandstone found in various places on the “Flattop Pene­ p lain,” som e fifteen miles from , and five thousand feet above, the nearest k n ow n Lyons outcrop suggest m inor dom estic tragedies am ong the early inhabitants o f the region .7 C ircum ferentially grooved quasi-spherical objects, found in various parts o f this area, som e on the surface, others at various depths b elow it, have been locally classified as stone hammers. A b ou t h a lf are actually stone ham m er heads, shaped from river boulders or p ot­ hole “ grinders.”8 O thers are concretions, found in strata o f various ages from Cretaceous to Recent. Edged Tools. Projectile points and stone knives found are chipped from jasper, chert, petrified w o o d , quartzite, and obsidian. Som e o f the material locally classified as petrified w o o d is actually banded jasper. Fragments o f projectile points, disregarded by m ost col­ lectors, are the best “in place” evidence n o w available at m ost sites. Edged fragments o f the various crystalline and cryptocrystalline silicates have been classed as scrapers unless there is definite evidence that they are projectile points, knives, or quarry chips. A ll the projectile points observed during this investigation lack the longitudinal blood gro o v e characteristic o f Folsom manufacture and are fairly generalized both as to shape and as to m aker’s technique. O n these edged tools, the larger flakes, usually called “face flakes,” seem to have been rem oved by percussion, the on ly dependable m ethod for use w ith n on uniform materials. Flaking o f this type can be readily duplicated by alm ost anyone after a few hours o f practice. A few o f the projectile points have been sharpened b y the rem oval o f fine chips at the edges. This marginal retouching was alm ost certainly done b y pressure, probably w ith a bone or horn tool.

M a n y o f th e artifacts fo u n d are m ade o f m aterials available in n u m ero u s places, n o t o n ly w ith in this reg io n b u t in adjacent regions. T hese ca n n o t be traced to a single p o in t o f origin, an d th eir value in d eterm in in g ancient trade, travel, and m ig ra tio n routes is slight. W ith in and near th e reg io n o n ly tw o artifact m aterials, v arieg ated jasp er an d w h ite quartz, are fo u n d in sharply defined areas. V arieg ated jasp er, usually red b u t occasionally b ro w n , green, w h ite, or tran sp aren t, is present as “ n ig g erh ead s” in one o f the lavas o f the T ab le M o u n ta in fo rm a tio n 9 and w eathers fro m it as large nodules at T able M o u n ta in (Fig. i) , w h ere it w as extensively w o rk e d (Fig. 3). R ather detailed field w o rk disclosed no o th er extensively w o rk e d source o f this ja sp er in eastern M id d le P ark. A t the head 1 N u m e ro u s finds o f fra g m e n ts o f se d im e n ta ry ro ck near th e su m m it of th e F ro n t R an g e far fro m , an d co n sid e rab ly ab o v e , p rc s c n t-d a y o u tc ro p s led a n u m b e r o f geolog ists to p o stu la te a f o rm e r tra n s­ ra n g e ex ten sio n o f P lains sed im en ts. S uch assu m p tio n s w e re n o t in ac co rd w ith o th e r ev id en ce, m o stly p a le o g e o g ra p h ic . W o r k by M iss J a n e Leas o f Las A nim as, C o lo ., w h o fo u n d th a t m a n y of th e fra g m e n ts co llected at th e A lb io n V alley site (S ite 2, Fig. i ) fitted to g e th e r in to a m e tate. co n v in ced local g eologists th a t a n y rock fra g m e n t fo u n d a b o v e its p ro b a b le source, an d sm all e n o u g h fo r a m a n to c a rry , is o f d o u b t­ ful g e o lo g ic significance. 8 R . L. Ives: T h e O rig in o f S o m e P o lish ed S to n e A rtifacts, Atner. A n tiq u ity, V ol. 6, 1940, p p . 70 -7 2 . 9 Ives, G lacial G e o lo g v o f th e M o n a rc h V alley, p. 1049.

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o f B ak er G u lch (Fig. i, site i) a v ein o f m assive w h ite q u artz, o f locally u n ­ m a tch e d c h ip p in g q uality, is exposed and w as extensiv ely w o rk e d . A few p ro jectile poin ts an d scrapers m ade o f obsidian o r w h ite q u artzite m a y be classified, w ith som e certain ty , as im p o rta tio n s. T h e finely chipped w h ite -q u a rtz ite artifacts fo u n d here are p ro b a b ly fro m th e h ead w aters o f the A rkansas, w h ere S aw atch q u a rtz ite ,10 o f variable b u t reaso n ab ly g o o d chip-

F ig . 3— S u m m it o f T a b le M o u n ta in , p av e d w ith chips o f v a rie g a te d ja sp e r, w h ic h co n sti­ tu te a b o u t tw e n ty p e r c e n t o f th e su rface m a te ria l. T h e la rg e lig h t-c o lo re d fra g m e n t, to the left o f an d a b o v e th e m u z z le o f th e re v o lv e r, is a c o re f r o m w h ic h ch ip s h a v e b een rem o v ed .

p in g quality , o u tcro p s an d w as w o rk e d in m a n y places. A lth o u g h local “ a u th o ritie s” state em p h atically th a t o b sid ian -arro w h e ad m a n u factu re was an im p o rta n t ab o rig in al in d u stry at S pecim en M o u n ta in , n ear th e P oudreC o lo ra d o d iv id e (U n ite d States G eological S urvey, R o c k y M o u n ta in N a ­ tio n a l P ark q u ad ran g le, C o lo ra d o ), field studies disclosed n o obsidian o f passable ch ip p in g q u ality there. L ocal flow s are so bad ly sh attered th at a piece o f u n cra ck ed obsidian h a lf an inch o n a side is h a rd to find. Field studies b y R a y 11 in the P o u d re V alley an d M edicine B o w M o u n ta in s disclosed no o bsidian o f g o o d ch ip p in g quality. T h e nearest k n o w n source o f w o rk ab le obsidian is E n g in e er M o u n ta in ( 37 0 42' N ., 107° 4 8 ' W .; E n g in e er M o u n ­ tain q u ad ran g le), in the San Ju a n R ange o f so u th w e stern C o lo ra d o . 1,1 C a m b ria n (U . S . Cieol. Survey Cieol. A tlas o f the U nited States Folio g, 1894, p- 6). 11 L. L. R ay: G e o m o rp h o lo g y an d Q u a te rn a ry C h r o n o lo g y o f N o r th e a s te r n C o lo r a d o ( D o c to r ’s T h esis, H a rv a rd U n iv e rs ity , 1938), p. 85.

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C am ps

R e p o rts o f an cient cam ps are n u m e ro u s in this reg io n , b u t g o o d evidence is scanty. N eb u lo u s evidence, such as one or tw o b ro k e n pro jectile points, fra g m en ts o f a m etate, o r an old fireplace, is p le n tifu l b u t m ay o n ly be indica­ tiv e o f a “ o ne n ig h t” cam p o r a sh o rt h alt in a m arch . T h e sites to be described seem to have been o ccu p ied fo r a ra th e r lo n g tim e. P ro b a b le uses w ill be in ferred fro m locations an d o th e r field evidence. A n cien t cam psites in th e Estes P ark re g io n have been described b y Y e lm .12 Baker Gulch. T h e Baker Gulch cam psite (Fig. i ) is at the top o f a small pass betw een Baker Gulch, in M iddle Park, and the south fork o f the M ichigan River, in N o rth Park. T he site is a cold and w in d -sw ep t “storm p ock et” just above timber line on the C ontinental D ivid e. “T epee rings” are num erous here, and also quarry chips o f w h ite quartz, w hich was extensively w ork ed near by. Som e o f the tepee rings are too small to hold d o w n the edges o f the usual tepee, and they are too large for fireplaces, particularly since all w o o d had to be packed uphill to the site. It seems probable that, although som e o f the “circles” m ay be tepee rings, m any, particularly the small ones on steep slopes (as m uch as 2 5 °), are stone p olygon s, produced b y frost action.13 “ Slump terraces,” called locally “Indian tent platform s,” and several large rock glaciers are present near by. M iscellaneous fragments o f jasper and gray vein chert w ere found here, together w ith scattered charred fragments o f bone, identified, w ith som e doubt, as O vis canadensis. Clim atic conditions at this site indicate that it could have been occupied o n ly during the m ountain summer. Its ch ief use was alm ost certainly for the quarrying and w ork in g o f the near-by deposits o f w hite quartz. Table M ountain. So far as field evidence goes, the Table M ountain site was a quarry only, since there are n o tepee rings, old fireplaces, broken metates, or charred animal bones in the vicinity. A lso, there is no perm anent water w ithin a m ile o f the ch ief accum ulation o f quarry chips. T h e great quantity o f siliceous debris at this site (Fig. 3) suggests that it was used for a considerable tim e as a source o f artifact material. In addition, the southeast end o f the mesa is an excellent look ou t, from w h ich gam e grazing on the w et m eadow s o f the Colorado and Fraser V alleys can be observed. The Arapaho Pass Sites. Four ancient campsites were located w ithin about a m ile and a h a lf o f Arapaho Pass, on the Continental D ivid e betw een M iddle Boulder and Arapaho Creeks (Figs. 4 and 5). Three are logical campsites, used today by fisherm en and m ountain­ eers; the fourth is in a storm pocket on the shore o f Lake D oroth y, a m ost unsuitable cam p­ site. T he N ev a Basin cam psite is just at tim ber line in a cirque at the head o f Arapaho Creek, on the north shore o f a shallow lake im pounded by a recessional m oraine o f M onarch age. Chips o f chert and jasper, foun d m ixed w ith gravel in the bed o f the stream draining this lake, gave first clues to this cam psite. Later investigation disclosed several old fireplaces, 13 O p. cit. 13 C . F. S. S h arp e: L andslides an d R elate d P h e n o m e n a (C o lu m b ia G e o m o rp h ic S tu d ies, N o . 2), N e w Y o rk , 1938, pp. 3 6 -3 7 a n d Fig. 5; W ilh e lm S a lo m o n : A rk tisch e B o d e n fo rm e n in d e n A lp en , Sitzungsber. Heidelberger A k a d . der W iss,, M ath.-iiatiirwiss. Klasse, 1929, N o . 5.

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alm ost entirely buried b y peat. T h ese w ere sh ow n to be artificial, rather than natural, stone arrangem ents by the presence o f charcoal near them , at depths o f as m uch as 14 inches b elow the surface. This cam p, from its location, is inferred to have served as an “ overn igh t stop for travelers from M iddle Park to the eastern flank o f the range.

F ig . 4 — A ra p a h o Pass, as seen fro m th e S o u th A ra p a h o T ra il. T h e s n o w -fille d c irq u e o n th e le ft sk y lin e h o ld s L ake D o ro th y . C lo u d s b e y o n d th e pass a re th e 1 0:00 a. m . p h ase o f the d a ily c o n v e c tio n cycle, w h ic h u su ally p ro d u c e s v io le n t h a ils to rm s o v e r th e pass in th e m id a f te rn o o n . T h e tra il crossing th e pass is m o d e rn ( a b o u t 1890) b u t re p u te d ly fo llo w s th e co u rse

o f a n o ld In d ia n trail.

T h e Lake D o ro th y site is above the pass, and above tim ber line, at an altitude o f 12,050 feet, on the rock-paved shore o f Lake D oroth y. N u m erou s chips o f jasper, chert, obsidian, and w h ite quartz have been reported here: investigation disclosed a few chips o f chert and

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jasper, a num ber o f old fireplaces, and several fragm ents o f antler, p oorly preserved. A jasper scraper (similar to that in Fig. 2) was found 18 inches b elow the surface just north o f the lake, but this was nonindicative, since a w h isk y-b ottle cap w as found in the same hole. D ep th o f burial is no criterion o f age at this site; for the surface consists o f loose slabs o f rock, w h ich are F ig . 5 — D e ta il m a p , s h o w in g to p o g ra p h y , o ld cam psites, an d trails in th e A ra p a h o Pass area. D a ta m o d ifie d f r o m th e U . S. G eo lo g ical S u rv e y R o c k y M o u n ­ ta in N a tio n a l P a rk q u a d ra n g le . “ R ip p le d ” c o n to u rs ju s t w est o f A ra p a h o G lacier a re ava lan ch e ch u tes {see F. E . M a tth e s: A v a ­ la n ch e S c u lp tu re in th e S ierra N evada o f C alifo rn ia , Bull. Internatl. Assn. oj Sci. H ydrology N o . 23 (6th G en eral A ssem bly, E d in b u rg h , 1936), R ig a , 1938, p p . 631 -637).

o

annually rearranged b y frost heave and creep. N o tepee circles w ere found here. Local legends say that this area was a neutral zone betw een the ranges o f the reputedly hos­ tile Arapahoes and U n c o m pahgre U tes and that they m et atop the pass to trade. I f this is true, Lake D oroth y was the logical “market place.” T he site in the Fourth o f July Cirque is on the south flank o f South Arapaho Peak. It is b o g g y , but adequately sheltered, and still serves as an overnight cam psite for m ountaineering parties. T h e site covers som e three acres and is floored w ith peat and w alled w ith talus. M ost o f the artifacts w ere found in channels cut b y m eltw ater from adjacent snowbanks. There are num erous fireplaces, m ost o f them m odern but a few dating back to Indian tim es. M any o f the ancient fireplaces resem ble those built to contain a m ountaineer’s “supper fire.” A m etate o f Dakota sandstone w as found, and “several bushels” o f artifacts have been carried aw ay by tourists. Materials in place are chips and fragments o f chert, jasper, w h ite quartz, and quartz­ ite. Several obsidian arrow points have been reported found. This site was probably used for an overnight cam p by travelers crossing the range via Arapaho Pass, for it is the last good campsite in tim ber on the east side. If local legends are to be credited, it also served as site for a base cam p for traders w h o used Lake D o ro th y as a market place. Just b elo w the Fourth o f Ju ly Cirque, on the floor o f Fourth o f July Gulch, a tributary o f M iddle B oulder C reek, the form er existence o f another cam psite is inferred from the finding o f num erous w orked fragments o f chert, jasper, and quartzite in gravels underlying and filling channels in local peat deposits. Stone patterns suggesting peat-engulfed fireplaces

4 58

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G E O G R A P H IC A L R E V IE W

are present, but no charcoal is associated w ith them . N o tepee circles w ere found As peat gro w th at this site is so rapid that excavations m ade in the 1890’s are already filled, it is prob­ able that the ancient campsite is d eep ly buried. In dry years this site probably served as an alternate to the one in the cirque above it, and during the late sum m er and early fall, after the first snow s, it is a m ore suitable campsite. Albion Valley. N ear the abandoned A lbion tow nsite, A lbion V alley (Fig. 1, Site 2), are a num ber o f old campsites. E vidence from this area is n ot entirely satisfactory; m uch o f the artifact m aterial has been rem oved b y the collectors, and the best cam psites are covered by buildings erected during the operation o f the S n o w y R ange M ine. T epee circles and fire­ places w ere reported foun d here b y “old -tim ers,” but o n ly a few fireplaces, age uncertain, exist today. Fragments o f a red-sandstone m etate and o f a w ell w orn stone hatchet were found here, and chips o f w ork ed variegated jasper and vein chert are collected at the rate o f “a hatful a season.” T his w as probably the site o f a hunting cam p, located here because o f g o o d tim ber and shelter and nearness to the alpine m ead ow s o f N iw o t R idge, where m oun­ tain sheep w ere plentiful until about 1890, and to the w et m eadow s o f the low er A lbion and Silver Lake V alleys, still the range o f num erous deer. Coal Creek. A cam psite o n the north bank o f C oal Creek (Fig. 1, Site 3) was described to the writer b y Charles M oore o f Eldorado Springs. Investigation disclosed that there had really been a series o f cam ps, lining the north bank o f the creek for several m iles and extend­ in g som e distance northw ard over the mesas. Apparently this area w as occupied for a con­ siderable tim e. T epee circles, fireplaces, and fragments o f artifacts m ade o f local materials are p lentiful, despite stripping b y collectors and obliteration o f m uch evidence b y recent aque­ duct construction. Fragments o f im ported artifact materials, particularly obsidian and white quartzite, are num erous. Buffalo bones in quantity have been reported found near by; hence this was probably a hunting cam p. Further research here seems desirable. O ther Sites. Field studies sh ow that a few chips o f artifact materials can be found in almost any level quarter section o f the region and that an old fireplace can be found on alm ost every reasonable cam psite. So m any artifact chips have been found at Granby, Grand Lake, N eder­ land, R ollinsville, and B oulder that the form er existence o f lon g-occu p ied campsites can be assumed w ith confidence despite the obliteration o f surface evidence. M an y chips o f w ork ed variegated jasper have been foun d on the shore o f M onarch Lake (Fig. 1), a m an-m ade reservoir, and there is reported to be an old cam p at the head o f the lake, on a flat beach, n o w obliterated by beaver w ork . C onditions at Brainard Lake (Sect. 4, T . 1 N ., R. 73 W ., R o ck y M ountain N ational Park quadrangle) resem ble those at Monarch Lake, but m ost o f the chips foun d are o f vein chert. A few broken quartzite projectile points have been uncovered in road excavations. A cam psite near Poudre Lakes (Sect. 4, T. 5 N ., R. 75 W ., R .M .N .P . quadrangle) is described by Y elm ,14 w h ose conclusions are confirmed b y recent discoveries by rangers and road workers. D a t in g

of

C am ps

C o m p le te failure o f th e artifact m aterials to indicate an y c u ltu re m o re specific th a n n o n -F o lso m an d n o n -Y u m a has m ad e necessary th e use o f o th er 14 O p. cit., p. 29.

COLORADO

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R E G IO N

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criteria fo r d atin g th e various cam psites. N o n e o f th e sites w ere used by Indians after 1879, fo r in th a t year th e last o f th e U tes w e re expelled fro m M id d le P ark. A ll th e specim ens fo u n d lack the sheen o f freshly b ro k e n sili­ ceous m aterials, a fact indicatin g ages o f m o re th a n fifty years. W h e n this sheen has w e a th e re d aw ay, little fu rth e r change takes place in th e surface ap p ear­ ance o f siliceous m inerals fo r m a n y centuries. It is often possible to relate the o ccu p atio n o f a site to som e phase in th e p h y sio g rap h ic d e v e lo p m e n t o f th e reg io n , and in th a t w a y to d eterm in e a m a x im u m age. It seems p ro b ab le th a t this m a x im u m age is considerably g reater th a n th e actual age; fo r m o st o f the terrace an d valley sites w ere n o t d ry en o u g h fo r h u m a n o ccu p atio n u n til m a n y decades after th eir fo rm a tio n . O f th e 15 datable sites ex a m in e d below , o n ly five w ere in existence befo re th e end o f th e F olsom o cc u p atio n o f the L in d en m eier site.15 I f th e general sim ilarity o f th e edged tools fo u n d here is tak en as evidence th a t th e y are all p ro d u cts o f the sam e general culture, and hence o f the sam e general age, th e n all th e an cient cam psites can be assum ed to have been o ccupied th ro u g h a p erio d b eg in n in g d u rin g o r after th e recession o f th e N e v a ice an d en d in g n o t later th a n 1879, a tim e in terv al lasting n o t m o re th a n 4000 years and, w h e n th e tim e necessary fo r glacial recession and the establishm ent o f v eg eta­ tio n is considered, h a v in g a p ro b ab le d u ratio n o f less th a n 3000 years. T h e stripped surface form ing the sum m it o f Table M ountain is definitely p ost-M iocene in age, but not definitely post-early-Pleistocene. This gives a possible m axim u m age o f con ­ siderably m ore than 1,000,000 years, a figure m ore than 40 times too great, even assum ing, contrary to all evidence, that the earliest k n ow n m en in N o rth Am erica occupied the site. O n the second terrace b elo w that on w hich the Stillwater moraines o f the M onarch V alley rest, and o n ly a few feet above the level o f the Fraser River, is the G ranby site. This terrace is tentatively correlated w ith the Arapaho A glacial stage, and a m axim u m age o f 35,000 years is assigned to it. T he B oulder and C oal Creek sites, at the western m argin o f the Plains, cover a num ber o f terraces. I f the ages o f these sites are assumed to be less than those o f the low est terraces on w h ich artifacts are found, both m ay be tentatively dated as very late W isconsin, n ot older than M onarch B, w ith a m axim u m age o f 13,400 years. A top the sam e terrace on w h ich are the “tw in n ed ” m oraines o f the Arapaho glacial stage (undivided) is the N ederland site, to w hich a m axim um age o f 35,000 years is assigned, w ith som e doubt because o f incom plete trans-range glacial correlations. Sites at the three large lakes in the region — M onarch, Grand, and Brainard— are 011 or near the surface o f wash contained betw een the M onarch B and M onarch C m oraines and hence cannot be older than the M onarch C m oraine. T o these sites a m axim um age o f 10,400 years is assigned. Is B ry a n an d R ay, op. cit., pp. 6 9 -7 0 .

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T h e A lbion V alley site is atop peat and outw ash upvalley from the M onarch C m oraine and hence cannot be older than 10,400 years. As b oth peat grow th and sheet deposition are rapid in this area, the actual age m ay be very m uch less. T h e rem aining datable sites— Baker G ulch, N e v a Basin, Lake D oroth y, Fourth o f July Cirque, Fourth o f Ju ly Gulch, and Poudre Lakes— all occu p y sites o f w h ich the gross forms w ere carved by the M onarch C ice about 10,000 years ago and the surface details, in which the artifacts are found, w ere produced during and after the recession o f the N e v a ice, not m ore than 4000 years ago. R e c o n s t r u c t io n

of

T r a il s

T h e fo re g o in g descriptions o f cam p an d q u a rry sites, o f th e m aterials fo u n d there, a n d o f local en v iro n m en ts sh o w conclusively th a t trav el to o k place b etw e en th e sites. R e co n stru c tio n o f th e ancien t trad e an d trav el routes resem bles a “ p ap er chase” th e trail sign fo r w h ic h is f ro m 60 to 4000 years o ld an d n o t alw ays clearly exposed. A lth o u g h th e “ trails o f chips” furnished p rim a ry evidence fo r these reco n stru ctio n s (Figs. 1 a n d 5), certain other features co n firm th e field inferences. In tracin g o u t these ancient trails, it w as assum ed th a t th e early travelers used th e shallow est fords an d th e easiest passes, chose sheltered campsites, p referre d firm g ro u n d to b o g o r talus, and, in general, h a d “trail sense.” This w as verified, in m a n y cases, by th e fin d in g o f o ld trails an d cam ps in such lo g ical locations. F ield w o rk w as g rea tly com p licated b y erro n eo u s local re p o rts; by th e presence o f glacially tra n sp o rte d artifact m aterials ad jacen t to fra g m en ts o f artifacts; by a general raising o f valley floors b y ancient and re c e n t beaver w o rk ; and b y m o d e rn constru ctio n . Trails in the Colorado and Fraser Valleys. From far western C olorado to the ColoradoFraser ju n ction an ancient trail follow ed the m ain C olorado Valley. Parts o f this trail are n ow U . S. H ig h w a y 40. From the ju n ction a branch o f this trail w en t eastward until it joined trails crossing the Continental D iv id e betw een N ev a and Jam es Peaks (see “U te Trail,” United States G eological Survey, Central C ity quadrangle, C olorado). A n extensive netw ork o f trails, fo llo w in g both sides o f the C olorado Valley, connected the Colorado-Fraser jun ction w ith Grand Lake. T h e m ain trail fo llo w ed a high terrace from the ju n ction to the m outh o f the Cam p Ouray canyon, w here it was join ed b y a short cut across the mesas from Granby and then passed through a w in d gap at the fo o t o f Table M ountain. From the base o f Table M ountain a trail crossed the flats o f the Stillwater basin to Soda Creek (Fig. 1), m eandered across the term inal m oraines to the ju n ction o f the Grand Lake outlet w ith the north fork o f the Colorado River, crossed the river at this point, and fol­ lo w ed the east bank o f the outlet to Grand Lake. Another branch w en t eastward from Table M ountain to the ford o f the Colorado at the m outh o f Arapaho Creek, w here an extensive cam psite has been obliterated b y recent construction, then proceeded up the east bank o f the river to the forks, where it join ed the other trail to Grand Lake.

COLORADO

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R E G IO N

461

N o rth o f Grand Lake, distribution o f w ork ed w h ite quartz from Baker Gulch indicates that travel m ust have occurred, but no continuous trail can be located. O ccasional sections o f old trail, in places overg row n by tim ber m ore than fifty years old, are present on the east terrace o f the C olorad o River, and chips o f w orked artifact material are occasionally found along them . R eports o f a campsite at the m outh o f O nahu Creek were investigated, and the “thousands o f arrow p oints” w ere found to be glacially transported fragm ents o f w h ite quartz and local obsidian. In the narrow canyon o f Beaver Creek, just b elow its forks (Sect. 17, T . 5 N ., R. 75 W ., R ock y M ountain N ational Park quadrangle), there are short sections o f old trail, overgrow n by tim ber and in places covered b y slum ped valley-w all material. This is apparently a part o f the “ O ld U te Trail” described b y Y elm .16 Pass Trails. C on n ecting the C olorado V alley w ith the eastern slope o f the range are a num ber o f trails that m ake use o f various natural passes. From Grand Lake a trail leads up the N o rth Inlet to N o rth Fork Ranger Station (Sect. 29, T . 4 N ., R. 74 W ., R ock y M ountain N ational Park quadrangle) and thence to the “ Flattop Peneplain,” where there is an old cam psite. Various points on this trail, w h ich is substantially identical w ith one described by Y elm , are indicated b y scattered finds o f artifact fragments, m ost o f them by C .C .C . workers during trail reconstructions. In the upper T onahutu V alley (Fig. 1), from Tonahutu B ig M eadow s (Sects. 17, 8, and 9, T . 4 N ., R. 75 W ., R ock y M ountain N ational Park quadrangle) to the “ Flattop Pene­ plain,” scattered artifact fragm ents give evidence o f an old, little-used trail. Scattered finds suggest that the T onahutu trail passed through a w in d gap west o f the m eadow s and joined the C olorado V alley trail near the m outh o f O nahu Creek. From the m outh o f Arapaho Creek to M onarch Lake an old trail is postulated on the basis o f several hundred scattered finds. T h e probable route coincides alm ost exactly w ith that o f the present M onarch Valley road. Short sections o f old trail w ere found in dense tim ber on the south w all o f the valley betw een the Colorado R iver and M onarch Lake. From M onarch Lake, w here at least on e ancient cam p has been subm erged, a trail fo l­ lo w ed the valleys o f Cascade and Buchanan Creeks to Buchanan Pass and thence through G host V alley to the St. Vrain V alley. N u m erou s artifact chips attest the existence o f this trail, but n o old camps were found along it, thou gh the trip from M onarch Lake to the eastern slope is m ore than a d ay’s jou rn ey for a party afoot. N o trace was found o f a reported ancient trail up Cascade Creek and over Paw nee Pass. Probably Paw nee Pass, until the recent construction o f a horse trail, w as too difficult for ordinary use by travelers. T he m ost used o f the ancient pass trails, as inferred from the am ount o f field evidence, w as that over Arapaho Pass, w h ich w en t from M onarch Lake up Arapaho Creek, across the pass, d ow n Fourth o f July Gulch to Eldora, and thence d o w n M iddle Boulder Creek to Nederland. This trail, still in use, is the easiest route for a man traveling afoot from the eastern foothills to M iddle Park. Short sections o f the old trail can still be found in tim ber in the upper part o f the Arapaho Creek Valley, and along them are m any chips and fragments o f w orked artifact material. Foothills Trails. In the foothills, from about 9500 feet d ow n to the Plains, is a rather 16 O p. cit., p. 32.

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extensive n etw ork o f ancient trails, m any o f w h ich fo llo w ed the same routes as the presentday roads. C on n ecting N ederland w ith the Plains (Fig. o) was a trail that fo llo w e d M iddle Boulder Creek to Boulder and thence to the W h ite R ock campsites. T his, evidenced by a surprising num ber o f artifact finds, is one o f the few ancient trails found in an area o f bad going. A nother trail from N ederland led along W in iger R idge, betw een M iddle B oulder and South B oulder canyons, to Skate Ranch (Blackhaw k quadrangle), then descended to the valley o f South B ou ld er C reek, passed through Eldorado Gap, and jo in e d the ancient trail connecting the C oal Creek and B oulder camps. A num ber o f alternate trails betw een Skate Ranch and the Plains are evidenced by scattered finds. From R ollinsville a “trail o f chips” goes south­ eastward through the lo w pass betw een T h orod in and T rem on t (Star) M ountains (Black­ h aw k quadrangle), b eyon d w h ich no trace o f it can be found. This is probably a section o f on e o f the U te trails from M iddle Park to the C oal Creek area. N u m erou s other trails are k n o w n , and descriptions o f them aw ait on ly the com p letion o f detailed field studies. A bsen c e of F o lso m

E v id e n c e

T h rou gh ou t this study the absence o f any evidence suggesting occupation o f the region by so-called “Folsom m an” has been noted. In v ie w o f the num erous studies m ade in the region, the extensive recent excavations, and the strong local interest in archeology, it w o u ld seem that absence o f Folsom finds indicates that F olsom m an did n ot occupy this region. A b o u t o n e -th ird o f th e re g io n did n o t h av e its presen t surface fo rm until F o lso m tim e. A t least an o th e r th ird is so b a rre n an d cold th a t it could n ot h av e been occu p ied b y p rim itiv e m an . In th e re m a in in g th ird a norm ally h ea lth y m a n , w ith a reasonably g o o d bed ro ll, can cam p o u t to d a y w ith o u t acu te d isc o m fo rt fo r a b o u t a h u n d re d days in th e year. O cc u p atio n o f the re g io n in w in te r by an y g ro u p n o t eq u ip p ed w ith shelter a t least as go o d as th e tepee, w h ic h F olsom m a n ap p a ren tly d id n o t have, is v irtu a lly impossible. C lim a te o n th e Plains d u rin g F olsom tim e, B ry a n an d R ay d ed u ce,17 was co ld er th a n at p resent an d “ sim ilar to th a t o f th e C a n ad ian G reat Plains.” T h e y suggest, logically, th a t p rec ip ita tio n in th e m o u n ta in s m a y have been h eav ier th a n o n th e Plains. E x tra p o la tio n o f these co n d itio n s to th e region co n cern ed gives M id d le P ark, d u rin g F olsom tim e, a clim ate like th a t en­ co u n tered to d a y at 10,500 feet d u rin g a w e t su m m er. U n d e r these conditions, n eith er F olsom m a n n o r th e anim als he h u n te d w o u ld h av e h ad an y reason to visit the reg io n . O n th e basis o f this evidence, seem ingly w ith in reason but lack in g th e “rig o ro u s m ath em atical p r o o f ” so o ften desired an d so seldom o b tain ed , it seems th a t search fo r F olsom evidence in eastern M id d le P ark is futile. 17 O p. cit., p. 72.

A

CULTURAL

HI ATUS

MOUNTAI N

IN THE

ROCKY

REGI ON

BY RONALD L. IVES

R E D ',rlU CA T ED FROM S O U T H W E S T E R N LO R E , VOL. VII, 1 9 4 1 , 4 2 - 4 6 .

SUBMITTED TO THE FACULTY O F THE GRADUATE S C H O O L IN PARTIAL FULFILLMENT O F THE R E ­ QUIREMENTS FOR THE DEGREE DOCTOR O F PHIL­ O S O P H Y IN THE DEPARTMENT O F GEOGRAPHY, INDIANA UNIVERSITY.

A C U L T U R A L H IA T U S IN T H E R O C K Y M O U N T A I N R E G IO N By R onald L Ives Boulder, Colorado

INTRODUCTION S tu d ies o f the p reh istory of the C olorado F ro n t R a n g e area, and of region s im m ed iately ad jacen t, u sin g both p h y sio g ra p h ic and archaeologic evidence, h ave produced sev era l chronologies,, n ot b y a n y m ean s in close a g reem en t, but all co n ta in in g in d isp u tab le elem en ts o f co rrectn ess. D esp ite the ch ron ological d iscrep a n cies r e su ltin g from the u se o f v ariou s ty p e s of evidence, it is ap p aren t th a t for a con sid erab le period a fte r the term in ation o f F olsom occu p ation there is no good ev id en ce th a t th e m o u n ­ ta in s and a d ja cen t p lain s a rea s w ere in hab ited . In th is sh o rt n ote, th e ev id en ce fo r su ch a cu ltu ra l h ia tu s wall be su m ­ m a rily p resen ted , and c lim a tic co n d itio n s d uring it b rie fly d iscu ssed .

FO LSO M O C C U PA T IO N R ec en t stu d ie s a t the L in d en m eier S ite, d iscovered b y C offin in 1934, sh o w th at, beyond an y reason ab le doubt, the cu ltu re la y e r is of la te g la c ia l age. P h y sio g ra p h ic in v e stig a tio n s by B ryan and R a y (1940) in d ica te th a t F olsom occu p ation took place b etw een twro periods of terra ce fo rm a tio n . B y m ean s o f ex te n siv e terra ce co rrela tio n s, th ese periods o f terra ce fo r ­ m ation are found to be a p p ro x im a tely co n tem p o ra n eo u s w ith the C orral C reek and L ong D raw g la c ia l s ta g e s a t the head o f th e C aeh e-L a -P o u d re R iver. B y m ean s of oth er lo n g -ra n g e co rrela tio n s, th e au th o rs arrive a t a g es o f ap p ro x im a tely 25,000 and 10,000 y ea r s for th e C orral C reek and Long D raw g la c ia tio n s, re sp ectiv ely . T h ese d a tin g s are still u n certain due in la rg e p art to the d isa g re em en t b etw een g la c ia l ch ron ologies in th e P oud re and C olorado V a lle y s (Iv es, 1940). The a g e o f the L ong D raw g la c ia l sta g e , 10,000 y ea rs, how ever, se e m s a t le a st reason ab ly correct, for s ta g e s a lm o st e x a c tly eq u iv a len t to it are p resen t in all m ajor trib u ta ries to the C olorado R iver, and oth er eq u iv a len ts have been noted in the E s te s P ark area by Dr. L. O. Q uam , of th e U n i­ v er sity o f Colorado. T his d a tin g, w hich g iv e s the m inim um a g e o f th e L ind en m eier S ite, m ay not be in error by m ore th a n 1,000 y ea rs, plus or m inus. M ore ex a c t d eterm in a tio n is im p o ssib le u ntil it is a scerta in ed w h e th er m axim u m terrace co n stru ctio n occurs at g la c ia l m axim a, or dur ing som e p hase of g la cia l recession . D iscu ssion of the problem o f the m a x im u m a g e o f the base of th e cu ltu re la y e r a t the L indenm eier S ite is fr u itle ss u ntil m ore d a ta co n cern in g m oun ­ tain g la c ia tio n s in the C olorad o-L aram ie-P ou d re h ea d w a ters a rea are a c ­ cu m ulated , and the p resen t d isa g r e e m e n ts of g la c ia l ev id en ce are resolved. A N T IQ U IT Y O F “M O D E R N ” I N D I A N S A rch aeologic evidence in d ica tin g an a n tiq u ity of four or fiv e cen tu ries tor the "modern" Indian cu lture of the R ocky M ountain region is p len tifu l, but little really valid evidence of this sort can be produced to sh ow th a t the a n cesto r s o f the p resen t In d ian s w-ere here m uch m ore than 2,000 y ea rs ago. P h y sio g ra p h ic evidence, w hich a lm o st a lw a y s g iv e s a b so lu te m axim u m a g e s, p lain ly sh o w s th a t the "modern" Indian w a s not here m uch m ore than ■1.000 yea rs ago, for even an cient a r tifa c ts rest on land su r fa c e s n o t older than the N ev a G lacial S ta g e , w'hich, by co rrela tio n w ith its C aliforn ia eq u ivalen t iM a tth e s, 1940 a -b t, the "L ittle Ice A ge", took p lace about 2,000 B. C.*. TH E PR E -N E V A C U L T U R A L H IA T U S F rom th e above d a tin g s, w hich are m a xim a, and w h ich in d ica te tim e lap ses probably con sid erably in ex c ess of a ctu a l v a lu es, it is ap p a ren t that Tin* m in o r glaciation had w o rld-w ide climatic effects, as lias noted hy m a n y w o r k e r s . l u i i o p . a n e v i d e n e i - is c i t e d h \ Daly, K A. T he t hnn^lnt; W o r l d o f t h e l e e A m 1, N o w M a \ - - n . I lull. 7 it - s 11. I n a r e a s m u i ci - ( o \ , | i d . w . a t e i le v ls in i n l a n d b a s i n s wa r e h m l o i i l i a n a t pie.-ont. A n t u Krnst: Pokil»l i i vt i i l P l l m n t l e \ u r l n t l o i i M i n t h e S i n i U n n ' s i , H u l l . A m M e t . S m - . V o l . ; a, t ' c ; \ l>. I t n i - 1 tCi. It s l m u l d h e n o t e d , a t l e a s t a s a n i n l e i , s t i n « c o i n c i d e n c e , t h a t t h i s p e r i o d o f h i g h w a t e r h \ e l s c o i n c i d e s i n a c e w i t h t i c N o n e hi a n I tchig>-. w l o c h l o o k p l a c e i n - :i IT It. ( ’ a c c o r d i n g t o H . h i e w e h r o m d o u i. > » ' o m s t o , k . ,| [, Out lines of tieolonj. New \ork, I s 1 1 , p. i f —

i:t —

th e tim e b etw een the term in a tio n of F o lso m o ccu p a tio n of the L indenm eier S ite and th e com m en cem en t of "m odern” o ccu p a tio n rem a in s to be accoun ted for. T he probable m inim um le n g th o f th is cu ltu ra l h ia tu s is fro m the clim a x o f th e L ong D raw g la c ia tio n , a p p r o x im a tely 10,000 y e a r s ago, to th a t of th e N ev a g la c ia tio n , w h ich probably b eg a n n o t m u ch m ore than 4,000 y ears ago. G eneral relation s are sh ow n in F ig. 1, a tem p oral colum n sh o w in g tim e-

MODERN AM ERICAN IN DIA N

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Fig.

19.

Hurricane trajectories in middle America during the calendar year 1936.

entered the Sonoran Desert, and one of these was, in all probability, a ‘‘glancing contact” . Few of the hurricanes or tropical cyclones which enter the mainland portions of the Sonoran Desert cross it, because only an exceptionally strong hurricane, under very favorable conditions of humidity and temperature, can continue in existence over a land area. Those few hurricanes which move inland, however, produce, in a few hours or days, in a restricted area, rainfall equal to or exceeding the annual average for the area. One very clear example of this, the hurricane of Sept. 30, 1921,30 brought 3.63 inches of rain to Yuma, Arizona, where the mean annual rain­ fall is about 3.47 inches. 30 Hurd, W . E. T ropical Cyclones of the E astern N o rth Pacific Ocean, U. S. Hydrographic Office, W ashington, Edition 4, 1944.

061950584525349494927619

07711822

Genesis and dissipation of a “cold dome”, showing the life history of an exceptional norther, as well as related phenomena.

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180 R o n a ld L . I ves

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Although observational data from this area are still not as complete as might be desired, it appears that an appreciable part of the rainfall variability of the Sonoran Desert (Fig. 5) is due to hurricanes, and to tropical cyclones of less than hurricane intensity .31 E xtension of the w eather-reporting networks of both the U nited States and Mexico, now under way as funds permit, may soon clarify the relation of tropical cyclones to rainfall variability in the Sonoran Desert. N orthers, known in Spanish-speaking areas as nortes, are not as common nor as intense in the Sonoran D esert as they are in the areas east of the Continental Divide, but they are im portant causes of agricultural and range losses, and a few of them cause very intense discomfort in those parts of the region where frost is nearly unknown. N orthers are outbreaks of very cold air, usually from the northern G reat Basin, which commonly occur when a very strong high pressure area “camps” over the Snake River headwaters. In many instances, the same high pressure that p ro ­ duces a norther in the Sonoran D esert also produces dense fogs in the G reat Valley of California, and chinooks in the foot-hills area in Colorado and Wyoming. Genesis and dissipation of an exceptional “cold dome” over the Idaho lava beds, with its characteristic accompaniment of California fogs, northers, and chinooks, is shown in Figure 20; an abridged version of a sequence of maps prepared by the U. S. W eather Bureau, with some data, secured from local observations, added. This particular norther, which brought frost and freezing temperatures to areas which had been frost-free for almost two generations, caused an enormous am ount of human discomfort, and may have damaged the endemic desert flora severely .32 A norther is usually accompanied by light to dense fogs over the Gulf of California, and more rarely over the Salton S e a ; and usually is preceded by a strong, dry, and rapidly-moving front, not always shown on synoptic maps. In some instances and areas, the cold air comprising the norther is relatively thin, and is separated from the superjacent air by a strong inversion. In parts of the lower Colorado Valley, some northers behave as density currents, and resemble, on a large scale, the katabatic winds characteristic of most mountain valleys. In a m ajority of instances, the air circulation comprising a norther in the Sonoran area is from the source high to the approximate center of the Sonoran Low (Fig. 18). O nly when the source high is particularly persistent, and the amount of air in transit is great, does the norther proceed far south of about Lat. 30° N. W hen this does take place (as in Fig. 20), the Sonoran Low is temporarily obliterated, and air motion is from the source high (usually in the Snake River lava Ives, R. L., “M exican W est-Coast Hurricanes,” Proc. Seventh Pacific Set. Cong, in press. The amount of plant damage caused by this norther is still a matter of conjecture. That the plant damage occurred and was evident in the summer of 1938 is undeniable, but a part of the damage seems due to disease, rather than to direct chill. It is entirely possible that local plants, such as the Saguaro cactus, are normally immune to local bacteria, but become susceptible after extreme chilling, in much the same manner that many healthy humans contract pneumonia after inhaling phosgene. Evaluation of the primary and secondary damage to vegetation as a result of northers and other climatic adversities is quite important agriculturally, but is in the realm of plant pathology, rather than of geography. 31

32

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plateau) to a low in the general vicinity of the O ceana B ank (L at. 9° N ; Long. 116° W .) . F orecasting of both tropical cyclones and northers in the Sonoran D ese rt area is a t present rath e r unsatisfactory, despite rath e r m arked im provem ents w ithin the last decade, because of the small num ber of reporting stations. T H E SO N O R A N M O N SO O N

Inspection of the pressure and w ind patterns of the Sonoran D esert and adjacent land and sea areas disclose a seasonal shift in the position of the Pacific H ig h ; a reversal of the pressure in the north ern G reat B asin from low in sum m er to high in w in te r; and a season variation in the size and intensity of the Sonoran low, which is largest and strongest during the hot season. T hese factors are qualitatively sim ilar to those producing the Indian M onsoon, yet the S onoran D esert is a region of m arked aridity, w hereas some places in the path of the In d ian M onsoon, such as C herrapunji, in the K hasi H ills (m ore than 400 inches of rain annually) are am ong the w ettest places on earth. D u rin g the sum m er season, the S onoran monsoon produces some heavy rains in th e higher p arts of the S onoran D esert and of the A rizona plateau region on its n o rth ern boundary, but these rains are heavy only by com parison w ith precipitation on the flatlands, and seldom exceed 60 inches, even in very small areas, such as the forest between M cN ary and Showlow (A riz. F ig. 2 ). M oderate to light rains occur over m ost of the desert area, and are due to convective uplift of the moist m onsoon air. A s the relative hum idity of this air, on the d esert floor, is low, uplift to 8 , 0 0 0 feet, or more, is usually necessary to produce precipitation. G eneralized air circulation p atterns during the sum m er show th a t the Sonoran M onsoon has a lateral infeed, receiving air from high pressu re areas at about Lat. 38° N. A ir entering the Sonoran D esert from the A tlantic H ig h is stripped of a large p art of its m oisture in transit across the Chihuahua— T ex an highlands, and is diluted w ith subsided superior air during its travels. In consequence, T ropical A tlantic air, as modified in transit, brings little available m oisture to th e Sonoran D esert. A ir from the Pacific H ig h is initially dry, because of descent, and picks up little m oisture in tran sit across the northeast Pacific, because of g reat stability and cool cu rren ts across its trajecto ry (F ig. 17). A p art of this m oisture is stripped out, before the air reaches the desert area, by crossing the S ierras and the peninsular ranges, and convective dilution occurs here also. Small inflows of very moist air are noted at tim es from th e T re s M arias vicinity to w ard the S onoran D esert. T his air, at its source, is nearly satu rated , but is w arm ed in transit, and diluted w ith convective retu rn air, so that, on arriv al near the A rizona— S onora boundary, its relative hum idity is low. T hus, although there is a definite inflow of air to the Sonoran D esert d u rin g the sum m er season, this a ir is not very m oist to begin w ith and it loses m uch of its relative hum idity and a sm aller p art of its specific hum idity, in tran sit. O therw ise

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stated, the loading and transporting mechanism of the Sonoran Monsoon is not very effective. Much of the notable precipitation from the Indian Monsoon is caused by the vertical deflection of the inflowing air currents as they cross the Himalayas (more than 15,000 feet high) to reach the low pressure area concentrated over the T arim Basin. In very marked contrast, the concentrated low in the Sonoran D esert is to windward of the Mogollon Rim (aerodynamically less than 7,000 feet high) during the summer season, so that much of the maritime air is dissipated in this low, and only a small p art rises over the highlands to produce orographic precipitation. In consequence, the Sonora monsoon is not only a poor bringer of m oisture to the Sonoran D esert, but has an inefficient dumping mechanism, so that it cannot pre­ cipitate much of the small amount of moisture which it does bring into the area. The w inter phase of the Sonoran monsoon is even more disappointing, con­ sisting only of interm ittent weak outflows of cold air from the northern Great Basin to the central Sonoran Desert. Little moisture is tran sp o rted ; there being a mini­ mum of m oisture picked up in the source area; an increase in tem perature tow ard the delivery a re a ; and little cause for moisture loss in the term inal area, which is the very weak w inter center of the Sonoran low. e x c e p t io n a l

areas

In the foregoing discussion, climate of the Sonoran D esert as a whole has been described, insofar as the evidence permits. The general average, however, is not the invariable condition, and many parts of the Sonoran Desert, due to relatively minor changes in topography or other factors, enjoy environmental conditions which are favorable to agriculture. M ost of the large settlements, such as Phoenix, Tucson, and Yuma, owe their existence to water diverted from rivers which originate outside of the desert. Many of the smaller settlements were founded as stage stations at places where streams or wells made w ater available. A typical oasis in this region is the town of Sonoita, Sonora (Fig. 1), on the ephemeral river of the same name. H ere, due to a happy combination of bedrock-alluvium relations, agriculture is not only possible but profitable, and perm anent w ater supply is avail­ able due to a funneling of the drainage of a large area through the deep canyon of the Sonoita River just east of the town. In prehistoric times, Sonoita was a semi-permanent or permanent agricultural settlement. A fter the introduction of livestock by Eusebio Kino in 1698, the local economy expanded. Since that time, by use of good sense and enormous amounts of hard work, the farm ing area has been expanded, the irrigation works improved, and numerous wells have been dug. The area now contains a prosperous and nearly self-sufficient farm ing community of about 800 persons. Although the return from attem pts at subsistence agriculture in typical desert areas is not equal to the seed planted, some desert areas, skilfully used, at exactly the right time, can be made to give a good return. The best example of this is the temporale agriculture of the Pim a-Papago people, who, as a result of careful

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observation and long experience, know exactly w here runoff from the erratic sum ­ m er rains will be concentrated and retained. By planting in these specially favored locations at exactly the rig h t season, as determ ined by several generations of ex­ perience, the P im a-P apago are able to raise excellent crops of corn and o th er foods about six years out of seven. W h en no rain w hatsoever falls in th e region, the crop is lost, as m ight be expected, but by planting in m any scattered areas, in different w atersheds, there is very seldom a “ starving year” despite th e vagaries of desert rainfall. A s nearly as can be determ ined from presen t evidence, this temporale agriculture has been practiced successfully by the P im a-P apago and related groups for m ore th a n 2 , 0 0 0 years. In the S onoran D esert there are also exceptional areas of another type— areas w here nothing will grow, even w ith irrigation. T hese consist of the g reat salt beds along the shores of the Gulf of California, the P inacate Lavas, and the saline floors of the larger play as. S U M M A R Y OF C L IM A T IC M E C H A N IC S

F ro m the foregoing descriptions, it should be apparent th a t th e Sonoran D esert is a tru e desert by any rational criterion, and th a t the rainfall is very deficient at all seasons. Causes of this regional aridity are, in sum m ary :— 1. D esiccation of air incom ing from the north, west, and east by passage over relatively high m ountain barriers. 2. D esiccation of air, incom ing and in place, by convective uplift, m ixing with subsiding “ H orse L atitu d e” air, and subsistence of the m ixture. 3. H eatin g of air incoming from the south, so th a t its relative hum idity is reduced greatly. 4. Southw ard location of the area relative to the m ean position of the Polar F ro n t. 5. O verall w eakness of the “ S onoran M onsoon,” and its inefficiency as a rainbringer. T his is due in large p art to the unfavorable location of physiographic features w ith respect to the regional pressure and w ind pattern.

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A

R E L A T IO N S

Many of the systems of climatic description now in use tend, by use of a “pigeonhole” classification, to mask the gradual transition from one climate to another, and to substitute for it, in the mind of the average student, a false concept of abrupt change. Several other systems, notably those employing De M artonne’s index of aridity, or a similar concept, successfully avoid the “pigeonhole” approach, but in so doing tend to conceal many other real and pertinent relations, such as the seasonal dis­ tribution of rainfall. By appropriating several of the concepts of electrical engineering mathematics, via harmonic analysis and electrical analogue computation, it is possible to describe most of the standard climates simply and tersely in term s of the familiar index of aridity, and the phase relationship of tem perature and rainfall. The phase relation can be stated most simply as the temporal relation between temperature maximum and precipitation maximum. Two illustrative examples of phase relations are shown in F igure 21 (to p ). In this figure, at Sao Paulo, the precipitation maximum leads (comes before) the tem perature maximum by about 30° or arc (one year being a complete cycle of 360°), or one month. A t this station, as at most other locations in the savanna, precipitation and temperature are very nearly in phase with each other (and w ith insolation maximum above the cloud level). In contrast, a t Tiberias, Palestine, an arid M editerranean station, the pre­ cipitation maximum lags (comes after) the tem perature maximum by about four months. Here, as at most other M editerranean stations, precipitation and tem pera­ ture are distinctly out of phase (in some instances by about 180°). At stations where the tem perature and precipitation curves are fairly simple, the phase relations can be determined, for ordinary descriptive purposes, by inspec­ tion. A more rigorous presentation is possible when the rainfall curve is quasisinusoidal, and rainfall distribution, in such an instance, may be approxim ated b y :—P = A + B Sin 9 In w hich:— P = Precipitation at any given time (short interval, such as one week) A = Mean rainfall for the year B = Maximum rainfall for a given time interval (same as in A ) during the year 9 = Time since rising precipitation curve crossed mean value, expressed as an angle (days elapsed divided by 365.244 and then multiplied by 360° : for most work, the relation days = degrees is adequate). Similarly, tem perature may be expressed by the form ula:— T = C + D Sin 9 and the phase difference between tem perature and precipitation, indicated by 9, is determined from the temporal difference between analogous parts of the curves, such as maxima. WhereaS tem perature curves may almost always be approxim ated by trigono-

186 SAO

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L. I v e s

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F i g . 21. Phase relations. T o p : Temperature— precipitation relations for upland savanna and M editerranean climate. B o tto m : E xam ples of pulse and m ixed rainfall regim es, with a simple pulse generator and its equations. Sym bols a r e :—

T c = time (seconds) necessary to charge condenser C to E f from Ee. T d = time (seconds) necessary to discharge condenser Cto E e from E f. C ~ capacity of condenser (fa ra d s). Eb = battery voltage. E f = firing voltage of neon tube. E e = extinction voltage of neon tube. R c = resistance of charging circuit (o h m s). R d = resistance of neon tube circuit (o h m s). Ineon = current in neon tube circuit (am p eres).

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metric formulae (not always as simple as the examples given), some rainfall curves are definitely not only nonsinusoidal, but appear to be logarithmic “attrition” curves, suggesting definite pulse or surge phenomena. Such a curve is shown on Figure 21 (Bom bay), where the rainfall pulse is produced by the breaking of the monsoon. The curved onset shown here is largely due to the variations in the tim ing of the monsoon, each individual year having a much sharper onset of the rainfall maximum than is shown by K endrew ’s mean value. Such pulse variations are common physical phenomena, and may be duplicated to any accuracy desired (except 100 percent) by a simple neon tube oscillator, (Fig. 21, center), or simple modifications thereof. In this device, monsoon rainfall is approximated b y . current flow through the neon tube circuit. By inserting in­ ductances at strategic points in the circuit, the various current and voltage curves can be modified to duplicate climatic curves of some complexity. By careful inspection, followed by elementary harmonic analysis, the various types of rainfall in a mixed regime can be isolated and evaluated. One example of this, the record for M azatlan, Sinaloa, at the northern edge of the western T ierra Caliente of Mexico, (Fig. 1; Fig. 21, right) is presented as an illustration. H ere, by inspection, it can be seen that the rainfall is dominated by a surge, in the summer season. Also plainly visible is curve of a relatively weak rainfall regime almost 180° out of phase with the tem perature curve. W hen the winter rainfall is ap­ proximated by a sine curve, whose value is subtracted from the totals, month by m onth; and the summ er rainfall is likewise represented by a fitted pulse curve, which is likewise subtracted from the to ta ls; the residual is a weak quasi— sinusoidal curve, roughly in phase w ith the tem perature curve, representing the savanna-type rainfall. Some stations have much more complicated rainfall patterns than this example. In very general terms, the following indications are given by tem perature— rain­ fall phase relations:— 1. W hen tem perature and rainfall curves are sinusoidal and nearly in phase, a dominance of convectional rainfall is indicated. 2. W hen the rainfall curve is a definite surge or pulse, taking place near, but not necessarily at, the tem perature maximum, or between two tem perature maxima separated by less than six months, a monsoon tendency is indicated. 3: W hen tem perature and rainfall curves are sinusoidal and four or more months out of phase, a dominance of frontal rainfall types is indicated, with a strong possibility of cyclonic storms, which reach a maximum at the time of maximum rainfall. These indications, it should be noted, are only approximate, and should be regarded only as rough w orking rules for which the practical limitations have not yet been determined. F u rth e r investigation and evaluation of this method of climatic analysis seems in order, as it, in conjunction with comployment of an index of aridity, or some similarly derived figure, offers some hope of producing a rigorous system of climatic description which does not suffer from the “pigeonhole” heresy inherent in the presently accepted systems.

WEATHER PHENOM ENA OF THE COLORADO ROCKIES

BY

RONALD L. IVES

Submitted to the Faculty of the Graduate School in partial fulfillment of the requirements for the degree, Doc­ tor of Philosophy, Department of Geography, Indiana Uni­ versity.

R e p rin te d fro m

th e J o u rn a l o f th e F ra n k lin

V o l. 2 2 6 ,

N o.

6. D e c e m b e r, 1938.

In s titu te ,

TABLE O F C O N T E N T S .

Introduction......................................................................................................................... Topographic Sum m ary..................................................................................................... Climatic Sum m ary............................................................................................................. Seasonal V ariations................................................................................................... Long-period Variations............................................................................................ Winter Storm s..................................................................................................................... Cyclonic Storm s......................................................................................................... Chinook W in d s.......................................................................................................... Minor Phenom ena..................................................................................................... Snow R edistribution........................................................................................ Cloud V eils......................................................................................................... Temperature Inversions................................................................................. Lunar Coronas................................................................................................... Sun D o g s............................................................................................................. Ice H a z e .............................................................................................................. "Snow S ta tic” ................................................................................................... Intermediate S ea son s........................................................................................................ Summer Storm s................................................................................................................... Cyclonic Storm s......................................................................................................... Regional S to rm s........................................................................................................ Typical Regional S torm ................................................................................. Effect of C yclones and A n ticyclon es......................................................... Areal Variations in Regional S torm s......................................................... Progressive Seasonal V ariations.................................................................. Interference Between Regional Storm s. . . Aerial Stratification......................................................................................... Explanatory H yp oth esis................................................................................ Valley Storm s............................................................................................................. Typical Valley S torm ...................................................................................... Effect of Cyclones and A n ticyclon es......................................................... Topographic F actors....................................................................................... Year-to-year V ariations................................................................................. Variations in a Single S ea so n ....................................................................... Barometric E ffects........................................................................................... Precipitation and Moisture T ransfer......................................................... Explanatory H yp oth esis................................................................................ Other P henom ena..................................................................................................... Cloud Plum es..................................................................................................... Electrical E ffects............................................................................................... Backdrafts.......................................................................................................... Conclusions........................................................................................................................... Possible A pplications........................................................................................................ G eology................................................................................................................ Irrigation............................................................................................................. A v ia tio n ............................................................................................................... Acknowledgm ents.............................................................................................................. Bibliography and N o te s........................................ 1

691 692 694 694 695 695 695 697 699 699

70 0 7°

2

703

7°4 7°4 7°5 7°6

7°7 7°9 7 11 7J5 7 J6 7l 9 72 0 721 72 1 724 72f> 729 73° 73 1 733 733 737 737 74° 740 743 74^ 74^ 75° 75° 732

753 754 754

L IS T O F ILL U STR A TIO N S. F ig u re

1. 2. 3 . 4 . 5. 6 . 7. 8. 9 . 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

H ypsom etric M ap of W estern Colorado................................................................ 6 9 3 Cloud V eil W est of Boulder, C olorado................................................................... 7 0 0 Diagram of C onditions Producing Cloud V e il.................................................... 70! A reas V isible in Figs. 5 , 6, and 7 . . ....................................................................... 7 * ° Sm all Cum uli and Cirri O ver N orth w est Q uadrant of M iddle P ark 712 Cum uli En Echelon Over S ou th w est Quadrant of M iddle P a r k ................. 7 J4 D isturbed Zone B etw een M iddle Park and T h e P la in s.................................. 7 I7 Cross Section of th e F ron t R ange D uring a Regional S to r m ....................... 7 1® D en ver Barograph Trace, A ugust 3 , 1 9 3 5 ............................................................ 72° Clouds in E astern M iddle Park D uring an A n tic y clo n e ................................ 723 M ap of th e M onarch V alley, Grand C ounty, C olorado.................................. 725 T h e M onarch V alley in M id m orn in g..................................................................... 727 Profile of th e M onarch V a lle y ................................................................................... 729 V alley Storm Clouds R ising in a C irq u e............................................................... 73 2 C um ulus H anging Over a C irq u e............................................................................ 734 Valley Storm Clouds Stream ing Through G aps in th e C ontinental D ivid e 7 3 6 C om parative Barograph Traces, D en ver and Boulder, July 1 8 - 2 1 , 1 9 3 3 . 7 3 ^ Enorm ous Cloud Plum e R ising from th e Longs P eak G roup....................... 74 1 Cloud Plum e F orm ation .............................................................................................. 743 Conditions Producing B a c k d ra fts............................................................................ 747

J o u orf n a l The Franklin Institute Devoted to Science and th e Mechanic Arts

Vol. 226

DECEMBER, 1938

No. 6

WEATHER PH E N O M E N A OF THE COLORADO ROCKIES. BY

RONALD L. IVES. ABSTR AC T.

From field observations in the mountain region of Colorado, it was determined that the major portion of the state's moisture is brought in by the winter cyclones. Winter winds redistribute the snow, and Chinook winds remove a portion of it from the mountain region and adjacent plains. Summer storms of three types tend to redistribute the moisture derived from melting snow. Two types, of alm ost daily summer occurrence, the regional and local or valley storms, are topographically-confined convection phenomena, which daily transfer small am ounts of moisture across divides. Cyclones tend to augment the violence of both other types; anticyclones inhibit the regional storms, but have a negligible effect on the local storms. Numerous barometric, electrical, and optical phenomena of great interest but minor clim atic im portance are briefly described. H ypotheses explaining the various major and minor phenomena are presented, and possible applications of the results of this and further studies of mountain weather conditions are suggested. IN T R O D U C T IO N .

M o u n ta in w e a th e r , in g e n e ra l, is re g a rd e d a s u n p re d ic ta b le , n o t o n ly b y v is ito rs to th e m o u n ta in reg io n s b u t also b y local re sid e n ts. “ O ld t i m e r s ” f re q u e n tly s ta te t h a t “ o n ly fools an d fla tla n d e rs t r y to p r e d ic t m o u n ta in w e a th e r ,” a n d th e c o n tra s t b e tw e e n a c tu a l a n d p re d ic te d m o u n ta in w e a th e r seem ingly c o n firm s th e lo cal o p in io n of w e a th e r p ro p h e ts . A m o re c a re fu l in v e s tig a tio n , h o w e v e r, sh o w s t h a t cy clo n ic sto rm s h a v in g th e ir o rig in f a r fro m th e m o u n ta in s a re q u ite a c c u ra te ly p r e d ic te d b y th e m e th o d s n ow in use, w h ile s to rm s by

(N ote— The Franklin Institute is not responsible for the statements and opinions advanced contributors in t h e J o u r n a l . ) VOL. 226, NO. 1356— 4 8 69I

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onald

L.

I ves.

[J. F. I.

originating in, near, or between the major mountain ranges cannot be predicted, by present methods, either much in advance, or with any great hope of accuracy. In this paper, some of the more frequently occurrent weather phenomena of the Colorado Rockies are described, and, where possible, partially explained. The observations here presented should be regarded as a preliminary survey of the problem of Rocky Mountain weather, and not as the final word on th at problem. Observations made by the writer during five years are included in this paper. The magnitude of the area, and the com plexity of the phenomena, suggest th at several generations of work, by a large number of observers, will be necessary before a complete understanding of the m any and complexlyinterrelated weather phenomena of the Rocky M ountains is obtained. W hile the data contained in this paper were secured in the Colorado Rockies, which are only a small part of the moun­ tainous portion of this continent, the sim ilarity of Colorado mountain weather to that in topographically similar regions elsewhere suggests th at conclusions drawn from these field data should apply, with some or much modification, to other mountain regions. T O P O G R A P H IC SU M M A R Y .

The Colorado Rockies, a series of very roughly parallel mountain ranges trending slightly w est of north and rising to a height nowhere exceeding 14,500 feet above sea level, have a general elevation of 8,000 feet above the plains, and rise approximately 5,000 feet above the interm ontane parks. First upraised from the drying Pierre sea toward the close of Upper Cretaceous time, the Colorado Rockies have been further uplifted a number of times since. (This number is currently in dispute.) Volcanic activity in Eocene and Miocene tim es altered the topography somewhat; the lava flows, ash and breccia deposits having a general smoothing effect on the topography of the intermontane basins. Repeated glaciation during Pleistocene time carved the mountains into approximately their present rugged forms, creating deep valleys in what was formerly a rather gently

Dec., 1938.]

W eather

of

th e

C olorado

R o c k ie s.

693

F ig . i .

WESTERN

COLORADO

PARK

ABOVE

BELOW

10, 5 0 0 '

7, 5 0 0 '

H y p so m etric

M ap

K ey to m o u n ta in ran g e s: 1. R a b b it E a rs R an g e. 2. M edicine Bow R a n g e . 3. N e v e r S u m m e r M o u n ta in s . 4. K e n o sh a a n d T a r ry a ll M o u n ta in s. 5 - P ik e ’s P e a k . 6. W e t M o u n ta in s. 7 - S angre d e C risto M o u n ta in s . 8. S ie rra B lanca. 9- C u leb ra R an g e.

o f

W e s te rn

C olorado.

10. 11. 12. 13. 14. 15. 16. 17. 18.

F ro n t R an g e. M o sq u ito R ange. G ore R an g e. F la t T ops. W h ite R iv e r M o u n ta in s. S a w a te h R ange. E lk M o u n ta in s. S a n J u a n M o u n ta in s. S a n M iguel M o u n ta in s.

to p o g ra p h ic d a ta fo r th is m ap w ere o b ta in e d fro m th e U . S. Geological S u rv e y 's Topographic o f Slate o f Colorado, 1 {500,000; lro m lo n g -ran g e p h o to g ra p h s ; a n d in a few sm all a reas from field notes. N o m e n c la tu re follows U . S. G . S . a n d C o lo rad o M o u n ta in Club u sag e.

694

R o n a ld

L. I v e s .

tJ- F . I.

ro llin g u p la n d . F r o m t h e to p o g r a p h ic h is to r y , i t m a y b e a s s u m e d t h a t w e a th e r p h e n o m e n a c a u s e d o r c o n tro lle d b y th e p re s e n c e of m o u n ta in m a s s e s c a n h a v e o c c u r re d to a g r e a t e r o r le sse r d e g re e sin c e P a le o c e n e tim e , w h ile th o s e c o n tro lle d b y th e p re s e n c e o f th e d e e p g la c ie r- c a r v e d v a lle y s c o u ld h a r d ly h a v e o c c u r re d p r io r to e a r ly P le is to c e n e .1, 2- 3 CLIM A TIC S U M M A R Y .

C o lo ra d o h a s a n a t y p ic a l te m p e r a t e c lim a te , w ith c o n ­ tin e n ta l e x tre m e s in te n s ifie d b y h ig h a l titu d e . P r e c ip ita tio n v a r ie s f ro m less t h a n e ig h t to m o re t h a n s ix ty in c h e s a n n u a lly , w ith r a in fa ll d is t r ib u t io n in th e m o u n ta in s v e r y ir r e g u la r a n d g r e a tly in flu e n c e d b y lo c a l to p o g r a p h y . V e g e ta tio n r a n g e s fro m p o s s ib le U p p e r S o n o r a n (re lic t? ) in th e in te r m o n ta n e b a s in s to A r c tic A lp in e in th e h ig h e r m o u n ta in a re a s . S u m m e r t e m p e r a t u r e s e x c e e d in g I i o ° F . a re se ld o m o b s e r v e d ; w in te r te m p e r a t u r e s b e lo w m in u s 4 0 ° F . a r e r a r e ly r e p o r te d , c h ie fly b e c a u s e few m o u n ta in r e s id e n ts o w n th e r m o m e te r s c a p a b le of in d ic a tin g lo w e r te m p e r a tu r e s . T h e b e h a v io r o f g a s o lin e a n d o th e r “ n o n f r e e z in g ” liq u id s in th e h ig h c o u n t r y s u g g e s ts t h a t w in te r te m p e r a t u r e s o c c a s io n ­ a lly a p p r o a c h m in u s 8 o° F . fo r s h o r t p e rio d s . S e a so n a l V ariations.

T h e s e a s o n a l s h if tin g o f th e c y c lo n e tr a c k s , n o r th w a r d in s u m m e r a n d s o u th w a r d in w in te r , d e f in ite ly a ffe c ts th e w e a th e r o f th e C o lo ra d o m o u n ta in re g io n , w h ic h is w ell w ith in th e c y c lo n e a r e a in w in te r, a n d a t i ts s o u th w e s te r n m a rg in in s u m m e r. A s a r e s u lt o f th e s h if tin g of th e c y c lo n e tr a c k s , w e a th e r p r e d ic tio n s in w in te r, w h e n c y c lo n ic s to r m s o r ig in a tin g fa r f ro m th e m o u n ta in s a r e th e p r e d o m i n a n t s to r m ty p e , te n d to b e q u ite a c c u r a t e ; w h ile in th e s u m m e r , w h e n m o s t s to r m s a re of lo c a l o rig in , p r e d ic tio n s a re f r e q u e n tl y e r r o n e o u s . A v e ra g e d iu r n a l te m p e r a t u r e r a n g e in th e m o u n ta in s r e a c h e s a m a x im u m o f a b o u t 4 0 d e g re e s (F .) in t h e s u m m e r , d e c lin in g g r a d u a lly to less t h a n 2 0 d e g re e s (F .) in m id w in te r . E x tr e m e d iu r n a l v a r ia tio n s o f m o re t h a n 6 0 d e g re e s (F .) h a v e b e e n n o te d , b u t a r e n o t c o m m o n a t e le v a tio n s of le ss th a n 1 2 , 0 0 0 fee t.

Dec., 1938.]

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R o c k ie s .

695

Long-period V ariations.

Numerous long-period variations in wind direction, precipi­ tation, and annual temperature range have been hypothecated for the Colorado mountain region. In general, the evidence for these changes has been quite nebulous, although minor shifts in the prevailing winds of certain small areas, and some disturbance of the small-scale local storm cycles, have definitely occurred in the past 40 years.4 Whether these changes are cyclic, progressive, or erratic is not surely indi­ cated by available evidence. That slight changes are now occurring, and have occurred several times in the post-IateWisconsin past, is definitely proven by variations in the thickness of ice layers in a number of glaciers in and near Rocky Mountain National Park.5 The present trend of climatic change in the mountain area of Colorado seems to be toward heavy wet late spring snowfall (1934-35-36-37), wet summers (1935—36), and irregular glacial recession (pre-1900—1937). On the plains east of the moun­ tains, rainfall in the last decade has been slightly less than that during the period of 1900—1928. Seemingly, wet mountain summers coincide with severe dust storms on the plains. Until more adequate rainfall records, at more closely spaced stations, have been kept for several generations longer, this apparent relation should be regarded as an interesting coincidence. W IN T E R ST O R M S.

Winter storms in the Colorado mountain region may be roughly divided into normal, predictable, cyclonic storms, which bring moisture into the area from “ outside” ; abnormal, erratic cyclones, not easily or accurately predictable, which usually originate in the Colorado mountains or adjacent parts of the Great Basin region; and Chinook winds, which remove moisture from the leeward slopes and adjacent plains. The prevailing westerly winds of the high country are an im­ portant factor in the redistribution of already-fallen snow. Cyclonic Storm s.

During the mountain winter, roughly defined as the period from October 1 to M ay 1, although it varies in length at

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[J. F . I.

various altitudes, and from year to year, about 25 cyclones, and an approximately equal number of anticyclones, normally pass over the mountain region of Colorado. Of these, about a third are first reported in or near the Aleutian Peninsula. Another third of the cyclones probably originate in the same region, but are not reported until they reach the United States, western Canada, or the Pacific Ocean off the west coast. M ost of the non-Aleutian anticyclones are first reported roughly w est of San Francisco. A few of the early fall cyclones originate in the Colorado M ountains. Those cyclonic storms th at originate north of latitude 450 and w est of longitude 120° are, in general, “ well behaved,” and the time of their arrival over the mountain region can be predicted with some confidence. Cyclones originating in the mountain region cannot be predicted there with any certainty by methods in use today, for the disturbances preceding a “ home grow n” cyclonic storm are practically identical with those of a local storm. Cyclones originating in the Great Basin region, or in areas farther west, but south of latitude 45°, tend to follow ex­ tremely irregular courses, at variable speeds, and to be difficult to predict. Probably the broken terrain, extreme diurnal temperature variations and low relative hum idity of the Great Basin have a pronounced effect on the upper atmos­ phere over that region. Analyses of the barograph, thermograph, and other records of the Denver weather station, for the purpose of determining relations between the various weather factors of the mountain region, have in them an elem ent of futility, for Denver weather is typical of neither the mountains nor the plains. Comparison of Denver weather with th at of the western United States as a whole, however, does shed some light on the problem of mountain weather, despite the “ unfortunate” location of the city of Denver. When weather elem ents of recognizably cyclonic nature are eliminated from considera­ tion, those remaining m ay be tentatively classified as of mountain origin, and in a few cases, the disturbance of which they are evidence can be roughly traced by referring to the records of cooperating stations in and near the mountains. The small number and irregular distribution of these

Dec., 1938.]

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697

cooperating stations, and particularly the lack of stations on the summits of the various mountain ranges, makes complete analysis of any local weather disturbance difficult and subject to considerable probable error. Cooperating stations are of necessity located at or quite close to settlements, where they can be attended with a minimum of inconvenience to the volunteer observer. On the semi-arid plains, settlements usually occupy atypical areas, where water supply, or shelter, or both, are above average. Hence, no matter how accurate the instruments, or how zealous and skilled the observer, reports from these stations are likely to convey an overoptimistic picture of areal weather conditions. A careful scrutiny of the weather reports from Colorado, and a comparison of these reports with weather actually en­ countered there during several winters, shows that more than 80 per cent, of the weather (precipitation, wind, temperature change) can reasonably be attributed to predictable dis­ turbances of a cyclonic nature. i\bout half of the remaining weather is associated with anticyclones that ‘‘hang up ’’ over the tangle of mountain ranges near the Colorado-WyomingUtah boundaries. A weather station located near Brown’s Hole (Fig. 1: lat. 40° 45' N., long. 108° 50' W.), at the head of Lodore Canyon, should, in a few years, shed considerable light on the mechanics of “ hung” anticyclones. In this area, the extreme relief (about 4,000 feet from the canyon bottoms to the plateaus, then another 4,000 feet or more from the plateaus to the mountain summits), and the “chimney effect” of the Green River canyons, are sources of continual erratic barometric variation, a possible factor in the delaying of anticyclones that cross the region, and a definite menace to airplane travel, particularly when navigation is by instruments alone. Chinook W inds.

From one to ten or more times during an average winter, Chinook winds sweep down from the mountains onto the plains at their eastern edge, raising temperatures many degrees in a few hours, removing much or all of the snow, and doing more or less property damage. The temperature changes during a Chinook wind may be logically explained on

698

R onald

L.

Ives.

[J. F . I.

the basis of altitude and hum idity changes, the difference between observed and theoretical temperatures being m ini­ mized when the rehumidification of the wind, during the early part of the storm, by the sublimation of snow on the leeward slopes, is taken into consideration.6 W hile a rapidly-moving barometric low, in m any cases, im m ediately precedes a Chinook wind, the trans-range pres­ sure difference created by it appears inadequate to m otivate these violent and long-continued winds. M any explanations of the causes of Chinook winds have been attem pted, m ost of them on the basis of areas of high and low barometric pressure. Unless the atmosphere is assumed to be of uniform cross-section at all times, meteorological reasoning on the basis of areas alone is hardly justified. Chinook winds are definitely three-dimensional phenomena, and search for their cause should likewise be conducted in three dimensions. Chinook winds are not restricted to the Colorado Front Range area, but occur throughout the R ocky M ountains, and winds closely resembling them have been noted in California and N evada. The “ W ashoe Zephyr” of the Comstock region, immortalized by M ark Twain, is perhaps the best known of these.7 In considering mountain winds, it should be borne in mind th at any surface wind, on crossing a mountain range, under­ goes changes in pressure, with accompanying temperature changes. If the hum idity also is changed, either by precipita­ tion or evaporation, further changes in air temperature may be expected. Hence, in the case of a dry wind, blowing from Middle Park (Fig. I , elevation about 8,000 feet) across the Front Range to the plains (elevation about 5,000 feet), a tempera­ ture rise of about 10 degrees (F.) may be expected, and is often observed. Evaporation by the wind, during its transit of the range, reduces its temperature. When precipitation from a m oist wind takes place as it crosses the range, a greater temperature rise is called for by theory. From this, it is apparent that the temperature changes occurring during a Chinook wind differ only in degree from those accompanying any windstorm. If the term Chinook is

Dec., 1938-]

W e a th e r

o f

th e

C o lo r a d o

R o c k ie s .

699

confined to violent, dessicating winds from the mountains, not associated with any major cyclone or anticyclone, which cause a temperature rise of more than 30 degrees (F.) in less than 24 hours, much confusion may be avoided. This should be regarded as a working definition, subject to revision as more data are determined. M inor P henom ena.

A number of phenomena, classified as minor because of the small areal extent of a single occurrence, but of consider­ able importance in the aggregate, or as indicators of more im­ portant weather conditions, have been noted in the Colorado Rockies. Most of these are common to the winter season of all high mountain ranges. Snow R edistribution .— Mountain snow, driven by high winds, frequently migrates great distances, even across di­ vides, during the winter. With a normal maximum snowfall of only ten feet, many high valleys on the western slopes of the major ranges fill with snow to depths exceeding thirty feet as a result of drifting. Considerable amounts of snow are carried from windward to leeward slopes by the winter winds, giving some eastward-draining streams a greater spring run­ off than the direct snowfall on their watersheds would indicate. Partially offsetting this migration of snow are the actions of Chinook winds, which tend to deposit snow on the windward slopes, and “ e a t” the snow to leeward. Most of the existing glaciers in the Front Range area owe their continuing existence to these wind actions. The neve fields, too small to maintain their dependent glaciers with the accretion from normal snowfall, are augmented by snow blown onto them from the windward side of the range. As the steep-walled cirques are “ dead areas” so far as the violent Chinook winds are concerned, nearly all the snow blown into them is retained. Snow piled atop the ice fields by wind also preserves these moribund glaciers by forming a protective blanket on their upper surfaces which, as a result, are not exposed until late in the mountain summer. In extremely favorable years, when the accretion due to snowfall and drifting is great, or melting is slight, or both, some of the snow blanket on the ice surface survives the VOL. 226, NO. 1 3 5 6 ----4 9

700

R onald

L.

Iv es.

[J. F . I.

mountain summer, and becomes an integral part of the ice field. During a mountain winter, with its succession of storms, snow may be carried great distances in a series of “ jum ps.” The normal westerly and northwesterly winds transfer it from the western to the eastern slopes of the ranges, while the Chinooks tend to dessicate the eastern slopes, only to drop F ig . 2.

C loud

V e il

W est

o f

B o u ld er, C olorado.

P h o to g ra p h e d fro m t h e U n iv e rs ity o f C o lo ra d o c a m p u s a t 10 a . m . , F e b . 7, 1935. T e m p e r a ­ tu r e s in B o u ld e r, e le v a tio n a b o u t 5.300 f e e t, w e re a b o u t 38 d e g re e s (F .) a t t h a t tim e . O n e h o u r la te r, a r e s id e n t of th e fo o th ills, 4 m iles w e s t o f B o u ld e r a n d a b o u t 3,0 0 0 f e e t h ig h e r, r e p o r te d b y te le p h o n e t h a t his th e r m o m e te r h a d b e e n s ta n d in g a t 16 d e g re e s fo r s e v e ra l h o u rs . D u r in g th e n e x t six h o u rs, w h ile t h e c lo u d v e il slo w ly d im in is h e d in size a n d fin a lly d is a p p e a re d , t e m p e ra tu re s in B o u ld e r d r o p p e d 48 d e g re e s.

the acquired moisture again, usually as snow, on encountering the western slope of the next major mountain range. Cloud V eils .— Cloud veils, a picturesque feature of the foot­ hills region during many winter days, are locally regarded as precursors of Chinook winds. A more careful investigation shows that they indicate thermal stratification of the air, and are precursors only of temperature change.

Dec., 1938.]

W eather

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C olorado

R o c k ie s .

701

Cloud veils indicate the contact between cold and warm air strata, and are practically identical in appearance whether the cold air stratum is above the warm, or below it. Conditions necessary for the formation of a cloud veil are still air, and a temperature difference between two adjacent air strata sufficient to produce condensation at their contact. It seems probable, from a study of weather conditions following the appearance of cloud veils where the foothills drop off abruptly to join the plains, that the air stratum apparently F ig .

3.

14^723^68273^71^67282070753278388475^34220

WARM

D ia g r a m

o f

C o n d it io n s

P r o d u c in g

C loud

AIR

V e il .

T h is cross-section of t h e p lain s-fo o th ills c o n ta c t show s c o n d itio n s d u rin g th e existence of th e cloud veil show n in F ig . 2. T h e a b se n c e of a clo u d veil on th e su m m it of th e F ro n t R an g e, n miles west of th is sectio n a n d 5.000 fe e t h ig h er, su g g e sts t h a t th e g ra d ie n t of th e u p p e r surface of th e cold air was g rea te r t h a n five d eg rees. T h is clo u d v eil follow ed q u ite closely th e su m m its of th e higher ridges of th e foothills, m a in ta in in g its lev e l b e tw e e n th e m b y “ b rid g in g ” th e n u m ero u s canyons leading dow n to th e plains fro m th e p e n e p la in .

causing the cloud veil is actually the wedgelike leading edge of an invading air mass which has been elevated by crossing the mountains. Temperature Inversions .— Isolated strata of abnormally warm or cold air, sandwiched between layers of air of approxi­ mately normal temperature, are so frequently encountered, usually by accident, in the mountain region that they may reasonably be assumed of almost daily occurrence. In most instances, there is no visual indication of the sharply defined warm or cold air stratum, so that, unless it is

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actually encountered by a mountaineer or aviator, it will pass com pletely unnoticed. Frequently an “ inversion” of this kind will last for some time, a “ warm zone ” or “ cold zone ” being noted part w ay up a mountain peak for several successive days, even in quite windy weather. It seems probable that these therm ally-variant air strata are related to the “ vanishing rain s” so often reported by residents of the plains region just east of the mountains. Rain is seen falling from clouds at a great elevation, such as 10,000 feet, but the moisture fails to reach the ground in the area under the cloud. When observed from the crest of a nearby mountain range, the rain definitely falls from the cloud, and drops normally for several thousand feet, then vanishes into a m isty zone far above the surface of the plains. A warm dry air stratum at this “ vanishing p o in t” would account for this seemingly m ysterious phenomenon. These “ vanishing rains,” likewise, might be used as evidence of temperature inversions. The genesis of these therm ally-variant air strata is not surely known, nor has the problem of their origin been very thoroughly investigated. It is here suggested (although the suggestion is hardly better than a careful guess) th at they are relict air masses, of small dimensions, torn from, and left behind by, major air masses during their transit of the mountain region. L u n ar Coronas .— During many nights of the year, in the mountain region, but most com monly during the winter, rainbow-colored coronas surround the moon, occasionally the brighter planets, and rarely the fainter planets and some of the brighter stars. These coronas are m ost common when highcountry temperatures are abnormally low, and are locally, with some correctness, regarded as precursors of a cold wave. In Boulder, Colorado, during a cold spell in December, 1932, a lunar corona was observed for eleven successive nights. T his is an extreme case, but one corona a week from October to M ay is not an abnormal frequency at th at location. These lunar coronas have been variously attributed to water droplets and to ice crystals suspended in the air.8 Seemingly “ filling half the sk y,” these coronas, when m eas­

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ured, are actually quite small, having a measured diameter of less than 25 degrees. At times, a small corona, having a diameter of not over 5 degrees, has also been noted, and rarely, both types are present simultaneously. The angle subtended by a corona is constant, but apparently decreases as the celestial body illuminating its cause rises from the horizon toward the zenith. The brilliance, also, in most cases, diminishes greatly when the light source rises to much more than 30 degrees above the horizon. (All of these measure­ ments were made with a Brunton compass, unsuited for night use, and may be in error 10 per cent, either way.) The brilliance of a large corona, as determined from a photographic plate, may be as much as 1/10 that of the moon. (This figure is correct only to a factor of two.) Sun D ogs .— Sun dogs, mock suns, solar halos and coronas are rather common features of the winter sky, occurring half a dozen times during an average winter. Completely-developed halo displays, complete with mock suns and side arcs, are less common, occurring not more than twice a winter. While their appearance is unpredictable, displays of this kind are most common during the early morning hours, while the sun is less than 45 degrees above the horizon, and in abnormally cold weather, when the air-suspended ice crystals necessary for their appearance are most numerous.9 No two successive solar halo displays are either identical or very similar. At Boulder, Colorado (lat. 40 degrees N .), the following observations were made, chiefly during notably unsuccessful attempts to photograph solar halo displays. The outer limits of the outermost visible side arcs were slightly more than 60 degrees away from the sun in two observed displays; slightly more than 40 degrees in three other cases. The vertical extent of the display (horizon to upper limit of highest visible arc) was less than 90 degrees in every case. Measurements of light intensity with a modified Weston Photronic Exposure Meter, hardly suited to the task, gave decidedly unsatis­ factory results. “ North light,” however, could be rather accurately measured, and decreased from 250 F.C. while the display was visible to just under 200 F.C. after it faded out. Normally, as the sun rises, “ north light” increases slightly in intensity. (The above figures are accurate to plus or minus 10 per cent.)

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Ice H a ze .— M inute crystals of ice, suspended in the winter air, frequently introduce ice haze, a phenomenon more apparent to the photographic plate than to the eye. N or­ mally, the range of a camera using infra-red-sensitive plates and the necessary accompanying filters is limited only by the horizon, although definition falls off slightly about 25 miles from the camera because of atmospheric turbulence and possibly from the scattering of infra-red light by large droplets of water and dust particles. In very cold weather, objects ten miles from the camera are slightly obscured by white haze, and their images on the plate slightly diffused. The ultimate range of the camera under these conditions is about 40 miles. Beyond this distance, everything "w hites o u t.” During weather of this kind, a panchromatic film, used with a light yellow filter (Wratten K -2), actually has a greater range than an infra-red-sensitive plate used with its filter. It would seem, from this, that ice crystals have the property of diffusing and reflecting light from both ends of the spectrum, with a minimum of diffusion roughly in its center. It should be noted that both photographic films and gelatine filters (however mounted) act abnormally at tempera­ tures of more than about 20 degrees below zero; films be­ coming brittle and somewhat erratic as to exposure, filters suffering from microscopic reticulation in the cement, which causes mild to severe diffusion of the image. Extreme cold also has a somewhat unfortunate effect on some lenses. Filter reticulation caused by cold may or m ay not " h ea l” when the filter is warmed up to room temperature. " Snow S ta tic ."— Static electrical disturbances, chiefly noted as interrupters of telephone, telegraph, and radio com­ munication, are common during the mountain winter, al­ though no thunderstorms occur within several hundred miles of the disturbed region. These "static storm s” are most intense during very cold weather when "sharp” snow is being blown around rather violently. Wire fences on the plains near the mountains frequently accumulate charges strong enough to knock over men or cattle, and som etim es spit sparks to nearby grounded objects. Plains residents occa­ sionally report sparks that jump as much as a yard from their fences. Experiments with several long, well-insulated wire

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fences failed to produce sparks more than four inches in length. A static charge producing a spark only one inch long is powerful enough not only to knock a man down, but to make him quite sick for several hours after he regains his feet. During snowstorms, in cold weather, radio programs re­ ceived in the mountain region are quite often blanketed by a steady low-pitched growling noise, quite similar to the drumming of a heavy rain on a wooden roof. This noise is locally attributed to the snowfall, it being hypothecated that minute static discharges take place as the snowflakes touch grounded objects. This disturbance is present whether the radio antenna is outdoors or in, and whether the receiver is powered from the transmission line or from batteries. Similar disturbances can be heard during some snowstorms by listen­ ing in on the rural open-wire telephone lines, or by connecting a headset between any two medium-sized metal objects, such as a stove and a bedspring. IN T E R M E D IA T E S E A S O N S .

The intermediate seasons, spring and fall, separating winter and summer, cannot be accurately defined by reference to a calendar, even when corrections for altitude are made, but are definitely determined by marked and abrupt “ breaks” in the weather. The mountain spring, a period of about two weeks, may occur at any time between May 10 and June 20, and is characterized by a “ run” of clear days. As a result of this clear weather, melting in the high country progresses rapidly, and floods of greater or lesser severity may be ex­ pected on the plains and in the intermontane parks. The beginning of spring very roughly coincides with the northward shifting of the cyclone tracks, while the end of spring and the beginning of summer is marked by the commencement of the summer cycle of regional and local storms. Fall, in the mountains, is likewise characterized by a “ run” of clear days, but is not so sharply defined as the mountain spring. Fall usually begins toward the end of August with a “ real” snowstorm, followed by from three days to four weeks of clear cold weather. Fall ends with a heavy snowstorm, which lays down the “ permanent” snow of that season.

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The beginning of fall alm ost exactly coincides w ith the cessation of the local and regional summer storms, and ends with the coming of the winter cyclones and anticyclones. The popular classification of spring and fall as definite seasons seems hardly justified in the mountain region, where these two “ seasons” are actually short periods of transition between cyclonically-controlled and locally-controlled weather phenomena. SU M M ER STO R M S.

Throughout the Rocky M ountain region, summer storms are of almost daily occurrence, and are called, in various places, the “ afternoon storm s,” the “ tw o o ’clock storm s,” or are named from the place of their apparent origin, as “ Taylor Park Storm s.” Field studies of mountain storms during five summers show th at many different types of storms occurred, and a number of classifications, m ost of them extrem ely complex, are possible. Classification of Rocky M ountain summer storms by three general types, which probably occur in most glaciated mountain regions, was decided upon, on the basis of origin. These types are: 1. Cyclonic Storm s, of extram ontane o rig in . 2. R egional Storm s, of m ountain origin, generally confined to one of the p a rk s or inter m ontane basins, and influencing areas of the order of 10,000 square m iles. j . V alley Storm s, usually originating in , an d confined to, one system of valleys. These storm s influence an area of the order of 200 square m iles.

Regional storms, from their mechanics, should, at least theoretically, occur to some degree in any m ountainous region containing broad intermontane basins, regardless of altitude, latitude, or other geographic factors. Valley storms should not be expected in regions of “ sm ooth ” mountains, where glaciation or intense recent erosion has not taken place. Steep gradients seem necessary for their occurrence. Several storms of the same type m ay occur sim ultaneously in adjacent topographic areas, seemingly w ithout mutual interference. These similar simultaneous storms m ay be

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classed as a single storm over the whole area concerned, or may be considered singly, on the basis of moisture origin. The latter seems the more logical method, for if the storm over one area is inhibited, storms over adjacent regions, unless also interfered with, proceed normally. Frequently, storms of two or more types will occur to­ gether, causing a violent storm, locally, and aptly, called, by its effects, a “ trash-mover and a gully-washer.” Storms of each type have a definite, although usually minor, effect on storms of other types occurring in the same general area within the succeeding 24 hours. ‘‘Pure cases” of any storm type are quite rare during the summer season. Cyclonic Storm s.

Major cyclones and anticyclones are infrequent during the summer season in the Colorado Rockies, and may be classified, with reasonable correctness, as abnormal phe­ nomena. The regular cyclone tracks are a considerable distance north of the Colorado-Wyoming line during most of this season. Even though they are abnormal, summer cyclones of distant origin can be, and usually are, predicted with some accuracy by methods now in use. Cluttering of the records by local disturbances, and interference with the normal progress of cyclones by phenomena not affecting the recording instruments, are the probably cause of most of the prediction failures. Cyclones of supposedly local origin, first reported over southwestern Colorado, are the “ black sheep” of forecasting, arriving at the first point of observation simultaneously with the barometric disturbances they induce, and passing so few stations in their erratic progress that their course cannot be accurately plotted until they have reached, or passed over some miles of, the plains. Many of these cyclones, origi­ nating, supposedly, in southwestern Colorado, have a life of only 18 to 24 hours, and vanish somewhere over Kansas or Nebraska. Observations of storms in the San Juan and San Miguel Mountains, reputed place of origin of some of these “ home grown” cyclones, by field workers of the U. S. Geological

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Survey and by Colorado M ountain Club parties, suggest that the true place of origin of these storms is not in the mountains, but in the canyon-trenched plateauland of the “ four corners” country of southeastern Utah. This region, not only at the contact of the mountains with the plateaus, but also near the southern lim it of the cyclone belt and the northern lim it of the monsoon like southwestern storms, is a critical, and at present, alm ost unstudied area. Continuous observations at several stations between the Colorado-Utah line and Natural Bridges National Monument, for a period of at least several years, and preferable for several decades, seem to offer the best method of determining the true origin of these atypical cyclones. Major cyclones and anticyclones, while usually foreign to the mountain area, are definitely affected by topographicallyinduced convections as they pass over the mountain region. Rainstorms (and occasionally snows), predicted and even sighted from the plains, are often “ hung u p ” at the crest of the Front Range by the sheet of rising warm air resulting from intense heating of the flatlands adjacent to the mountains. It seems probable that many of the rains so fervently prayed for in the dustbowl are disappointingly light because the moisture-laden air from “ ou tside” has been diluted w ith hot desiccated air rising from the very region that m ost needs the rain. Like the proverbial snowball rolling downhill, this condition seems to get worse the longer the drought continues, and leads to an apparent shifting of precipitation from the plains to the mountain region. This shift was particularly notable in the summer of 1936, when for days at a tim e it rained steadily in the mountains, while the only precipitation on the plains was choking yellow dust. From these observations, it may be hypothecated that the total annual precipitation in Colorado is much more constant than the rainfall records, m ostly based on plains precipitation, indicate. As most of the effective mountain precipitation eventually reaches the Colorado River drainage, this seeming inverse relation between mountain and plains precipitation is of considerable importance at the present time, when a number of transmountain water diversion projects are under considera­ tion. If rainfall measurements show th at a water shortage on

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the plains, chiefly in the Platte and Arkansas drainages, is actually accompanied by increased precipitation at the head­ waters of streams draining into the Colorado, then trans­ mountain diversion projects should be effective in ameliorating the recurrent water shortages in the sugar beet country of the plains. If, however, the inverse relation of mountain to plains precipitation is found by detailed measurements to be more apparent than real, the value of some of these trans­ mountain diversion projects is definitely open to question. Cyclones, in general, tend to increase the intensity of local storms, upset their normally rather regular timing, and lower the temperatures, occasionally changing the “ daily rain” to a summer blizzard. Anticyclones, on the other hand, have an inhibitory effect on local storms, fo r one day only. After causing one clear day, an anticyclone, however long it may hover over the mountain region, has no further observable effect on the local summer storms. R egional Storm s.

Regional storms, securing the major part of their moisture from a definite area in the mountain region, and dropping their moisture on almost exactly the same area, are convectioncaused phenomena. These storms, affecting areas of the order of 10,000 square miles, are of almost daily occurrence during the summer season, although their intensity varies greatly from day to day. In the aptly-descriptive language of the Middle Park rancher, these storms “ try every day, but don’t always make it.” Storms of this type regularly occur over North, Middle, and South Parks, and over the San Luis Valley, which, from a topographic viewpoint, should also be classed as a park. Taylor Park (Fig. 1, lat. 38° 50' N., long. 106° 35' W .), topo­ graphically intermediate between a true park and the melting basin of a relatively large extinct glacier system, has its own series of storms, not easily fitted into any of the classifications previously set up.10 While each park, with its largely self-contained storms, is a separate case, not exactly resembling any other, the general mechanics of the regional storms is basically the same wher­ ever they have been observed. More than 200 storms of this

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type were encountered in the field during the summers of i 932_I936, inclusive, as well as a number of som ewhat F i g . 4.

CRAI G O

-40 N

jArapaho Peak

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MI L E S

A r e a s V is ib le in F ig s . 5. 6, a n d 7. T h e s h a d e d a re a s o n th is m a p c o rre s p o n d to t h e p h o to g ra p h e d a re a s in t h e th r e e follow ing fig u re s (F igs. 5, 6 . a n d 7). T h e d o tte d b o u n d a ry of e a c h field s e c to r re p r e s e n ts th e h o riz o n in its r e s p e c tiv e p h o to g ra p h . H ig h a ltitu d e s k y f e a tu re s f a r b e y o n d t h e la n d h o riz o n , a re , of co u rse, v isib le in e a c h p h o to g ra p h . A lth o u g h t h e th e o r e tic a l lim it o f t h e ra n g e of a c a m e ra is in fin ity , a tm o s p h e ric h a z e a n d a e ria l tu rb u le n c e lim it t h e p r a c tic a l r a n g e t h ro u g h th e a tm o s p h e re , e v e n w ith t h e in fra -re d -s e n s itiv e p la te s u sed in m a k in g th e s e fig u re s, to a b o u t 300 m ile s. C u r v a tu r e of t h e e a r t h a n d b ro k e n to p o g ra p h y lim it th e ra n g e , fo r la n d f e a tu re s , to a b o u t 160 m iles, in th e C o lo rad o R ockies.

atypical storms, probably, but not certainly, regional. It is entirely possible that some of these atypical regional storms

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w ere, in re a lity , u n re c o g n iz e d “ co m p o u n d s to r m s ,” w ith th e effect of th e d is tu r b in g s to r m c o m p o n e n t of r a th e r sm all m a g n itu d e c o m p a re d to t h a t of th e re g io n a l c o m p o n e n t. A v ailab le fa c ilitie s h a v e n o t, to d a te , p e r m itte d a s tu d y of th ese “ c o m p o u n d s to r m s .” T y p ic a l R eg io n a l S to r m .— R e g io n a l s to rm s a re u su a lly q u ite s im ila r in th e ir v a r io u s m a n ife s ta tio n s , th e in te n s ity of o ccurrences, r a th e r th a n th e ir seq u en c e, b e in g th e m a jo r v a ria b le . A ty p ic a l s to r m se e m in g ly s t a r t s b efo re su n rise , w h en a th in h aze, n o rm a lly n o t e x te n d in g m o re th a n a few fe e t a b o v e th e g ro u n d , a p p e a r s in th e lo w er p a r ts of th e in te r m o n ta n e basin o r p a r k . F ro m th e p re v io u s m id n ig h t u n til d u s t b e g in s blow ing s h o r tly a f te r su n rise (th is is th e n o rm a l “ v a g r a n t ” d u st of a se m i-a rid reg io n , n o t to b e co n fu se d w ith th e d en se clouds of d u s t c o m p risin g a d u s t s to rm ), th e sk y is in te n se ly clear o v e r th e p a rk s , ev e n a n in fra -re d p h o to g r a p h failin g to reveal th e f a in te s t tr a c e of a clo u d . D u rin g th is tim e, th e surface a ir is still, h u m id a n d cool. A b o u t a n h o u r a f te r su n rise , th e h az e d is a p p e a rs , a n d as the a ir b eco m es w a rm e r a n d d rie r, “ v a g r a n t ” d u s t b eg in s to blow . A few v e r y te n u o u s c irru s clo u d s, s u rro u n d e d b y a fain t w h ite n e b u lo s ity , p o ssib ly su sp e n d e d ice c ry s ta ls , a p p e a r v ery h ig h in th e a ir (a b o v e 17,000 fe e t), a n d slow ly d r ift across th e sk y fro m w e s t to e a st, a p p a r e n tly u n a ffe c te d b y th e reg io n a l a n d v a lle y s to r m s w h ich o c c u r la te r in th e d a y . P ro b a b ly th e se c lo u d s h a v e n o co n n e c tio n w ith th e reg io n a l sto rm s, th e c irr u s lev el b e in g fa r a b o v e th e n o rm a l u p p e r lim it of c o n v e c tio n . T w o h o u rs, m o re o r less, a f te r su n rise , a few sm a ll c u m u li ap p e a r a t v a rio u s lo c a tio n s o v e r th e p a r k (F ig . 5), a t a m edium e le v a tio n (1 4 ,0 0 0 -1 6 ,0 0 0 feet, a n d in c re ase in size a n d o p ac ity as th e y slo w ly d r if t ac ro ss th e sk y to w a rd th e e a s t and s o u th e a s t. T h e s e local c u m u li te n d to “ pile u p ” in th e so u th e a ste rn q u a d r a n t of th e p a rk , u n til th e s k y is a b o u t 75 per ce n t, o b sc u re d . T h is a c c u m u la tio n of c lo u d s c o n tin u e s u n til m id -a fte rn o o n , th e p o rtio n of th e sk y 75 p e r c e n t, o b sc u re d v a r y in g fro m storm to s to rm . A ra p id cooling of a b o u t 20 d eg re es (F .) ta k es place o n th e su rfa c e u n d e r th e c lo u d e d sk y a re a .

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As the clouds "pile u p ” at the eastern and southeastern margins of the park, they have a typical “ en echelon” appear­ ance, and their lower surfaces lie in a definite "plane.” Aviators report that the upper surface also is "a plane, with holes in it.” F i g . 5.

Sm all

C um uli

a n d

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N o rth w est

Q uadrant

o f

M id d l e

P a r k .

T h e c u m u li in th is p ic tu r e a re rid in g a m o v in g a ir s tr a tu m a t a n e le v a tio n o f b e tw e e n 14,000 a n d 16,000 f e e t w ith a v e lo c ity of less t h a n 36 m ile s p e r h o u r. T h e c irri, w h ic h h a v e b e e n " f u z z e d ” b y t h e ir v e r y ra p id m o tio n , h a v e a n e le v a tio n in e x c ess of 17,000 fe e t. T h is p h o to g ra p h , ta k e n fro m A ra p a h o P e a k , 13.500 f e e t a b o v e s e a le v e l, w ith a n in fr a -r e d p la te , in c lu d e s p a r t s of t h e P a rk a n d N e v e r S u m m e r R a n g e s (F ig . 1, n u m b e rs 2 a n d 3) a n d t h e g la c ia te d v a lle y o f t h e u p p e r C o lo rad o . T h is a r e a is c o n ta in e d in t h e " G r a n d L a k e ” s e c to r of F ig . 4. T h e c lo u d c o n d itio n s h e re sh o w n firs t a p p e a r a b o u t tw o h o u rs a f t e r su n ris e , a n d la s t fo r v a ry in g p e rio d s , t h e e x a c t tim e d e p e n d in g o n th e q u a d r a n t of t h e p a r k th e y a re o v e r a n d th e i n te n s ity o f t h e s to r m . T h is p h o to g r a p h w as t a k e n a t 2:30 p.m. o n A u g u s t 3, 1935.

B e tw e e n tw o a n d f o u r in th e a f te r n o o n , t h e c lo u d s b e c o m e v e r y b la c k , c h a n g in g f ro m c u m u li to c u m u lo - n im b i, o b s c u rin g t h e w h o le s k y . D u r in g t h i s c h a n g e , w h ic h p r o g re s s e s f ro m th e e d g e s o f th e c lo u d e d a r e a in w a r d to w a r d t h e c e n te r , a d e f in ite d is t u r b e d z o n e a p p e a r s w h e r e v e r c lo u d s h a v e c r o w d e d o u t o v e r a m o u n ta in r a n g e . T h is d i s t u r b e d z o n e is a lm o s t c e r ta in l y t h e r e s u lt o f th e in te r a c t io n o f th e p r e v a ilin g w in d s , w h ic h

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te n d to d riv e th e c lo u d s e a s tw a rd , th e th e r m a l ex p a n sio n of th e en tire a e ria l c o n te n t of th e p a r k , a n d th e c o n v e c tio n c u r r e n ts a lm o st u n iv e rs a lly p r e s e n t o n a m o u n ta in slope. T h e d is ­ tu rb e d zone follow s v e r y r o u g h ly th e c r e s t line of th e ran g e , b u t is n o t v is ib ly in flu e n c e d b y m in o r to p o g ra p h ic fe a tu re s, such as p a sse s o r e x tra -h ig h p e a k s (F ig . 6). W ith th e c h a n g e of c lo u d ty p e o v e r m u c h of th e p a r k fro m cu m u lu s to c u m u lo -n im b u s , th e re is a g e n e ra l q u ie tin g of th e a ir w ith in th e p a r k , a n d a n in c re a se in th e v o lu m e of th e d is ­ tu rb e d zo n e. F ro m it, sm a ll d e n se b la c k sc u d c lo u d s m o v e ra p id ly a w a y fro m th e m a in clo u d m ass, a n d g y r a te w ild ly in th e fo rm e rly c le a r a ir on th e le ew ard side of th e m o u n ta in range. T h u n d e r a n d lig h tn in g o cc u r, a lm o s t in v a ria b ly , b u t are la rg e ly co n fin ed to th e d is tu rb e d zon e a n d th e scud clouds. T h is p e rio d of c a lm in th e v a lle y a n d tu rb u le n c e on th e h eig h ts m a y la s t fro m a few m in u te s to o v e r a n h o u r, d u rin g w hich tim e p re s s u re s in d ic a te d b y a b a r o m e te r o n a n y h ig h p o in t v a r y r a p id ly , re p e a te d ly , a n d irre g u la rly fro m e x tre m e ly high to e x tre m e ly low fo r th e p a r tic u la r a ltitu d e . T h e p r e m o n ito ry ca lm e n d s su d d e n ly w ith v io le n t e r ra tic w inds a n d in te n s e d o w n p o u rs fro m th e scud clo u d s, follow ed by h e a v y ra in fro m th e d is tu rb e d zone (F ig. 7). W ith in a few m in u tes, m o d e ra te ra in falls fro m th e e n tire m a ss of cu m u lo n im bi. H a il is a c o m m o n o c c u rre n c e in th e m o u n ta in s d u rin g th e ra in y p h a s e of a re g io n a l sto rm , b u t is n o t n e c e ssa rily an in d ic atio n t h a t r a in d r o p s h a v e b ee n c a rrie d to a n y v e ry g r e a t h e ig h t b y risin g a i r c u r r e n ts . W ith a ir te m p e r a tu re s a t 1:3,500 fe e t o n ly 40 d e g re e s (F .) w h en th e sk y is o v e rc a s t (th e y often go b elo w fre e z in g in th e la te e v e n in g ), a ra in d ro p n eed only b e lifte d a b o u t 2,500 fe e t to e n te r a s tr a t u m of freezin g te m p e ra tu re . T h e n e c e s sa ry e le v a tio n is a b o u t t h a t of th e u p p e r “ p la n e ” of th e re g io n a l clo u d s tr a tu m . D u rin g th e r a in y p h a s e of a reg io n a l sto rm , so m e of its clouds m a y “ e s c a p e ” fro m th e a re a o v e r th e p a r k b y cro ssin g th e m o u n ta in rim , a n d tr a v e l w ith th e w in d fo r d is ta n c e s as g re a t a s f o rty m iles, d ro p p in g som e m o is tu re d u rin g th e ir w anderings. T h e e le v a tio n of th e se “ e s c a p e d ” clo u d s d e ­ creases im m e d ia te ly th e y h a v e cro ssed th e m o u n ta in s , a n d averages o n ly a b o u t 2 ,000 fe e t a b o v e th e g e n e ra l su rfa ce (Fig. 8).

7i4

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Iv es.

A f t e r r a t h e r v io le n t p r e c ip ita tio n u s u a lly la s tin g f o r a b o u t fifte e n m in u te s , b u t o c c a s io n a lly c o n tin u in g f o r a s lo n g a s tw o h o u r s , t h e c lo u d s r a t h e r s u d d e n ly “ b r e a k ” a n d d is s o lv e in a v e r y few m in u t e s . T h e s u n c o m e s o u t, a n d r a p id e v a p o r a tio n o f t h e n e w ly -fa lle n r a in ta k e s p la c e . A n h o u r o r F ig . 6.

C um uli

e n

E chelon

o v e r

South w est

Q uadrant

o f

M id d l e

P a r k .

T h e c u m u li h e re a r e “ p ilin g u p ” in t h e s o u th a n d s o u th w e s t p o r tio n s of M id d le P a r k . T h e ir e le v a tio n is b e tw e e n 14.000 a n d 16,000 f e e t. O n e sm a ll c lo u d m a s s in t h e u p p e r le f t c o rn e r of th is p ic tu r e h a s b e e n to r n lo o se fro m t h e m a in m a s s b y ris in g a ir c u rr e n ts , a n d fo rm s th e e x tre m e w e s te rn m a rg in o f th e “ d is tu r b e d z o n e ” o v e r t h e F r o n t R a n g e . T h is p h o to g ra p h , t a k e n w ith in a few s e co n d s of F ig . 5 > fro m t h e s a m e lo c a tio n (th e c a m e r a w a s m e r e ly t u r n e d o n t h e p a n n in g h e a d of t h e tr ip o d ), in c lu d e s p a r t s o f t h e G o re , S a w a tc h , M o s q u ite a n d F r o n t R a n g e s (F ig . r , n u m b e r s 12, is , xi. a n d 10) a n d is t h e A s p e n s e c to r in F ig . 4. T h e lo n g v a lle y in t h e m id d le d is ta n c e is t h a t of th e F r a s e r R iv e r, a t r i b u ta r y of th e C o lo ra d o . B e y o n d t h e v a lle y a re t h e V a s q u e z M o u n ta in s , a g la c ie r-fre tte d m in o r ra n g e .

so o f co o l c le a r w e a th e r g e n e r a lly in te r v e n e s b e tw e e n th e e n d in g o f th e re g io n a l s to r m a n d s u n s e t. W h ile th e re g io n a l s to r m is g o in g o n , s to r m s o f le s s e r m a g ­ n itu d e — th e v a lle y s to r m s — a lso o c c u r, n o t n e c e s s a r ily in e x a c t s y n c h ro n is m w ith t h e re g io n a l s to r m s , a n d a p p a r e n tly u n in flu e n c e d b y th e m e x c e p t a t th e e x tr e m e h e a d s o f th e v a lle y s , w h e re in te r fe re n c e b e tw e e n s to r m s ta k e s p la c e .

Dec., 1938-]

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E ffect o f Cyclones a n d A n tic y c lo n e s .— C y c lo n e s a n d a n t i ­ cyclones of m a jo r p r o p o rtio n s h a v e a d e fin ite a n d p a r tia lly p re d ic ta b le effec t on th e re g io n a l s to rm s of th e C o lo ra d o R ockies. C yclones, in g e n e ra l, b r in g a b o u t a lo w erin g of th e te m ­ p e ra tu re , d e te c ta b le in th e lo w er p a r ts of a p a rk , a n d p r o ­ nou n ced o n th e m o u n ta in s s u r ro u n d in g it. T h is le ad s to an increase in c lo u d in e ss, a n d a lo w erin g of th e level of th e clouds of a re g io n a l s to r m b y se v e ra l h u n d r e d , o r, in e x tre m e cases, se v e ra l th o u s a n d , fe e t. T h is lo w erin g b rin g s th e b o tto m of th e c lo u d s tr a t u m b elo w th e s u m m it of th e v a lle y w all, co n fin in g th e s to r m e v e n m o re rig id ly th a n d o th e rising a ir c u r r e n ts p r e s e n t o n d a y s of n o rm a l w e a th e r. T h e tim in g of th e re g io n a l s to r m s is, a s a r e s u lt of th is s h iftin g of th e cloud lev el a n d lo w e rin g of th e te m p e r a tu re , c o m p le te ly d isru p te d , a n d o n d a y s w h e n c y c lo n e s p a s s o v e r th e m o u n ta in region, th e r a in s m a y b e g in b e fo re n o o n , a n d c o n tin u e u n til long a f te r s u n se t. W ith th e d o w n w a rd s h if tin g of th e n o rm a l re g io n a l cloud level, th e re g io n a l a n d v a lle y s to rm s m u tu a lly in te rfe re , so t h a t d iffe re n tia tio n b e tw e e n c lo u d s o r p r e c ip ita tio n of th e tw o sto rm ty p e s is w e ll-n ig h im p o ssib le . If, in a d d itio n , as o fte n occurs, th e cy c lo n e is a c c o m p a n ie d b y a m a ss of clo u d s fro m “ o u ts id e ,” th e ta n g le of in te r fe rin g s to rm s is p ra c tic a lly b eyond a n a ly sis, a n d a lm o s t a n y th in g m a y h a p p e n . I t is these “ m ix e d s t o r m s ” t h a t b rin g su m m e r b liz z a rd s w ith th u n d e r a n d lig h tn in g to th e m o u n ta in reg io n , an d cau se o th e r se em in g ly a n o m a lo u s p h e n o m e n a . A n tic y clo n e s, n o r m a lly b rin g in g w a rm a ir in to th e m o u n ­ ta in region, te n d to in h ib it th e d a ily re g io n a l sto rm s, a n d bring a b o u t a to ta lly c le a r d a y . W a rm in g c a u se d b y a n t i­ cyclones is s lig h t a t low e le v a tio n s, b u t c o n sid e ra b le on th e heig h ts s u rro u n d in g th e p a rk s . T h e te m p e r a tu r e rise p r o ­ duced b y an a n tic y c lo n e s o m e tim e s a m o u n ts to 15 d e g re e s (F .) a t 14,000 fee t. T h e n o rm a l “ clo sed c i r c u i t ” of a ir a n d m o is tu re c irc u la tio n in th e p a rk s is c h a n g e d to a n “ o p e n c i r c u i t ” b y th e a lte r a tio n in th e rm a l g r a d ie n t in d u c e d b y a n a n tic y c lo n e . H e a te d a n d m oistened a ir fro m a p a rk , u n d e r th e s e co n d itio n s, no lo n g er sto p s risin g a t a l titu d e s of fro m 14,000 to 16,000 fee t, b u t VOL. 226, NO. 1 3 5 6 — SO

716

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[J- F . I.

a s c e n d s s e v e ra l th o u s a n d f e e t h ig h e r, m ix e s w ith th e e a s tw a r d m o v in g a i r of th e “ tr a d e w in d ” s t r a t u m , a n d is c a r r ie d r a p id l y a w a y fro m th e a r e a o f its o rig in . T h is r e s u lt s in a d e s s ic a tio n o f th e p a r k s , a n d a te m p o r a r y r e d u c tio n in th e t o t a l w e ig h t of a i r c o n fin e d b e tw e e n t h e ir w a lls. P a r tia lly o f fs e ttin g t h i s a i r a n d m o is tu r e r e m o v a l a r e th e v a lle y b re e z e s t h a t s p r in g u p d u r in g th e e v e n in g o f a c le a r d a y , a n d th e a c c e le r a te d m e ltin g o f m o u n t a i n sn o w fie ld s c a u s e d b y th r e e o r m o re a d d i tio n a l h o u r s o f s tr o n g s u n s h in e d u r in g th e h o t t e s t p a r t of th e a n tic y c lo n e - in d u c e d c le a r d a y . U s u a lly , a n a n tic y c lo n e c a u s e s o n ly o n e d a y o f c le a r s k y , a f t e r w h ic h th e th e r m a l g r a d ie n t, a lth o u g h n o t th e a v e r a g e te m p e r a t u r e , r e tu r n s to n o r m a l, a n d th e r e g io n a l s to r m s s t a r t a g a in , o f te n r a t h e r fe e b ly , w ith t h e r e g io n a l c lo u d s t r a t u m s e v e ra l h u n d r e d f e e t h ig h e r t h a n u s u a l. I t is c o m m o n ly s ta te d t h a t a n tic y c lo n e s i n h ib i t c o n v e c tio n , b u t t h e i r p r im a r y effe c t o n m o u n ta in s to r m s s e e m s to b e a n in h ib itio n of c o n d e n s a tio n a t n o r m a l le v e ls, w ith a r e s u l t a n t r e d u c tio n of p r e c ip ita tio n a n d a n in c re a s e in e ffe c tiv e in ­ s o la tio n . A r e a l V a r ia tio n s in R e g io n a l S to r m s .— N o tw o p a r k s in th e R o c k y M o u n ta in re g io n a r e to p o g r a p h ic a lly id e n tic a l. E a c h p a r k h a s its o w n o u tlin e , d e p t h , a n d w a ll g r a d ie n t, a n d a ll of th e s e f a c to r s h a v e a d e fin ite , a lth o u g h n o t a lw a y s im p o r ta n t, e ffe c t o n th e s to r m s o r ig in a tin g in t h e p a r k s , a n d la rg e ly o c c u r rin g o v e r th e m . I n g e n e ra l, a to p o g r a p h ic m a p o f a p a r k d r a w n to a sc ale o f o n e in c h to te n m iles, w ith a c o n t o u r in t e r v a l of 1,0 0 0 fe e t, sh o w s all th e f e a tu r e s t h a t in flu e n c e r e g io n a l s to r m s . V ie w e d o n ly fro m th e s ta n d p o i n t of r e g io n a l s to r m s , N o r t h a n d M id d le P a r k s (F ig . 1) a r e th e m o s t p e r f e c tly b o w l­ s h a p e d , a n d in th e m th e s to r m s b e h a v e in th e m o s t c o n s is te n t m an n er. S o u th P a r k , w ith a to p o g r a p h ic o p e n in g t o th e e a s t, is a r a t h e r im p e r f e c t b o w l, b u t th e s to r m s th e r e c lo s e ly re s e m b le th o s e in th e tw o p a r k s f a r t h e r n o r th , w ith th e e x c e p tio n t h a t a g r e a te r n u m b e r of s to r m s “ e s c a p e ” to th e e a s t. T a y l o r P a r k , p r e v io u s ly m e n tio n e d , is n o t a ty p ic a l p a r k a t a ll, a n d d o e s n o t, a s a r e s u lt, h a v e s to r m s c lo s e ly re s e m b lin g th o s e ty p ic a l of th e tr u e p a r k s .

D ec., 1938.]

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T h e S a n L u is V a lle y , to p o g r a p h ic a lly a p a rk , h a s reg io n a l sto rm s t h a t d iffe r c o n s id e ra b ly fro m th o se in th e o th e r p a rk s, because of d iffe re n c e s in la titu d e , a ir c u r r e n ts , w a te r s u p p ly an d v a lle y w all g r a d ie n t. H e re , th e w a te r su p p ly is ch iefly from th e S a n J u a n M o u n ta in s , w ith sm a ll a d d itio n s of m o istu re fro m th e S a n g re d e C risto , B la n c a a n d C u le b ra F ig .

D is t u r b e d

Zone

b e t w e e n

7.

M id d l e

P ark

an d

t h e

P l a in s .

C um ulo-nim bi in th e le ft h alf of th is p ic tu re a re bein g v io le n tly to ssed a b o u t b y th e a ir c u rre n ts rising from th e p lain s 8,000 fe e t belo w th e p e a k s a n d fifteen m iles to th e e a st (note m otion d u rin g exposure). A t th e rig h t a re th e cu m u li o v e r M id d le P a rk . In th e c e n te r, on th e horizon, ov er G ra y ’s a n d T o r re y ’s P e a k s, is a v io le n t rain a n d h a il s to rin , asso c ia te d w ith th e regional storm o v e r M iddle P a rk . In th e f a r d ista n c e , to th e rig h t, a re th e cum uli of th e regional sto rm o v e r S o u th P ark, which “ b r o k e ” w ith in a few m in u te s o f t h a t o v e r M id d le P a rk . T h is p ictu re, th e “ S ilver Plum e ” se cto r o f F ig. 4, sh o w s a b o u t 6 0 m iles of th e F ro n t R an g e (F ig . 1, n u m b e r 10), from A ra p a h o Peaks s o u th . T h is p h o to g ra p h w as ta k e n im m e d ia te ly a fte r F ig s. 5 a n d 6, from th e sam e trip o d setup. T h e sto rm h e re sh o w n c a u se d p re c ip ita tio n o v e r th e D e n v e r a re a as well as in th e p a rk s.

R an g es (F ig . 1, n u m b e rs 17, 7, 8, a n d 9). W ith a lesser av erag e r e la tiv e h u m id ity , c o n d e n s a tio n in a ir risin g fro m th e valley, w h ic h is a lm o s t a d e s e r t b a s in , w ith s c a n ty a rid v e g e ta tio n , p la y a s , s a n d d u n e s a n d b lin d d ra in a g e s , d o es n o t ta k e place a t 1 4 ,0 0 0 -1 6 ,0 0 0 fe e t. E v a p o ra tio n -m o is te n e d a ir rises to g r e a t h e ig h ts , w h e re it m ixes w ith th e e a s tw a rd -m o v in g a ir of th e “ tr a d e w i n d ” s tr a tu m , a n d tr a v e ls r a p id ly to w a rd

7

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th e e a s te r n w a ll o f th e v a lle y . T h e r e , i t is u p lif te d b y th e ris in g v a lle y -w a ll a ir c u r r e n ts , a n d a fe w m ile s f u r t h e r e a s t is u p lif te d a g a in b y u p d r a f t s o r ig in a tin g o n th e p la in s , a n d fo llo w in g th e e a s te r n fa c e of th e W e t M o u n ta in s (F ig . I , n u m b e r 6). T h is le a d s t o h e a v y p r e c ip ita tio n in t h e W e t M o u n ta in V a lle y , th e " L a M o j a d a ’’ o f t h e o ld S p a n is h m a p s . B e tw e e n th e a ir c u r r e n ts ris in g f ro m t h e S a n L u is V a lle y a n d th o s e fro m th e p la in s , th e r e is a m in o r " c lo s e d c i r c u i t " s y s te m o f s to r m s o v e r t h e W e t M o u n ta in V a lle y . T h e n o r m a l m e c h a n ic s o f th e " d a i l y s t o r m s ” o r ig in a tin g in th e S a n L u is V a lle y c lo se ly r e s e m b le s t h a t o f th e o t h e r p a r k s to r m s d u r in g th e firs t d a y o f a n a n tic y c lo n e . T h e u lti m a t e F ig . 8.

PENEPLAIN

C r o s s - s e c t io n

o f

t h e

F ront

R ang e

D u r in g

a

R e g io n a l

Storm .

C o n d itio n s sh o w n d ia g r a m m a tie a lly in th is fig u re a re s im ila r to th o s e s h o w n p h o to g ra p h ic a lly in F ig . 7. M in o r a ir c u rr e n ts a re n o t sh o w n a n d to p o g ra p h y h a s b e e n g e n e ra liz e d fo r t h e s a k e of c la r ity . H o riz o n ta l in te r v a ls a re o n e m ile e a c h ; v e rtic a l in te r v a ls a r e o n e t h o u s a n d f e e t e a c h .

e ffe c t of th e d a i ly h e a tin g is o n e o f d e s s ic a tio n in th e S a n L u is V a lle y , w h ile in th e o t h e r p a r k s m u c h o f t h e e v a p o r a te d m o is tu r e is r e g u la r ly r e s to r e d to it s a p p r o x im a te s o u rc e . G iv e n a g r e a te r w a te r s u p p ly , p e r h a p s tr ip le th e p r e s e n t a m o u n t, i t se e m s p r o b a b le t h a t t h e r e g io n a l s to r m s o r ig in a tin g in th e S a n L u is V a lle y w o u ld d r o p t h e i r m o is tu r e b a c k i n t o th e v a lle y , a n d c lo se ly re s e m b le th o s e o r ig in a tin g o v e r th e o th e r p ark s. T h e re g io n o f th e h e a d w a te r s o f t h e G u n n is o n R iv e r (F ig . i ) s o m e w h a t re s e m b le s a p a r k , b u t d o e s n o t h a v e a n y v e r y r e g u la r re g io n a l s to r m s , d u e p e r h a p s to t h e o p e n n e s s of th e b a s in t o th e w e s t. E r r a t i c a n d u n p r e d ic ta b l e s q u a lls a re c o m m o n in th is a r e a , a n d a s tr o n g " c h im n e y c u r r e n t "

D ec., 1938.]

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of

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C olorado

R o c k ie s .

719

u su a lly blo w s u p th e v a lle y so m e f e e t a b o v e its floor, c a rry in g e v a p o ra te d w a te r u p w a rd a n d e a s tw a rd b e y o n d th e to p o ­ g ra p h ic co n fin e s of th e u p p e r G u n n iso n V alley . I t seem s p ro b ab le , a lth o u g h g o o d e v id e n c e is la ck in g , t h a t so m e m o istu re of G u n n iso n V a lle y o rig in e v e n tu a lly falls as ra in in th e W e t M o u n ta in V a lle y . Progressive S ea so n a l V a ria tio n s.— W h ile s tr ic tly co n fin ed to th e m o u n ta in su m m e r, re g io n a l s to rm s a re n o t of u n ifo rm in te n s ity d u r in g t h a t se a so n . In g e n e ra l, th e ir in te n s ity rea ch es a m a x im u m d u r in g e a rly J u ly , a f te r w h ic h th e y g ra d u a lly “ ru n d o w n ” a n d o c c a sio n a lly “ m is s ” a s th e season progresses. T h e se in te n s ity v a r ia tio n s m a y b e a t tr ib u te d to se v eral fac to rs, of w h ic h th e tw o m o s t im p o r ta n t seem to b e th e d e ­ crease in a v a ila b le w a te r a s th e su m m e r goes on, a n d th e lessening of in s o la tio n o c c u rrin g a t th e sa m e tim e . W ith less w a te r to e v a p o r a te a n d less e n e rg y a v a ila b le fo r e v a p o ra tio n , th e a m o u n t of w a te r e v a p o r a te d r a p id ly d e c reases, as d oes th e reg io n al p r e c ip ita tio n , w h ic h is la rg e ly of local o rig in . W h ile d e c re a s e d p r e c ip ita tio n is a clue to th e “ w e a rin g o u t ” of th e s e sto rm s , a b e t t e r c rite rio n is th e ab sen c e of th e afte rn o o n clo u d b a n k w h en o th e r c o n d itio n s a re n o rm a l. T h is a lm o s t n e v e r o c c u rs u n til th e p a r k s a re th o ro u g h ly d esiccated , s tro n g ly s u g g e stin g t h a t la ck of w a te r, r a th e r th a n som e o th e r, a s y e t u n d e te r m in e d , force is in h ib itin g th e regional s to rm s. As m ig h t b e e x p e c te d , th e s to rm s in th e S a n L u is V alley , th e s o u th e rn m o s t p a r k in th e a r e a u n d e r c o n s id e ra tio n , a re th e first to s to p fro m la c k of m o is tu re . L a te r , th o se of S o u th P a rk b eco m e e r r a tic , a n d so m e tim e s cease. R e g io n a l s to rm s o v er M id d le a n d N o r th P a r k s u s u a lly c o n tin u e u n til th e e n d of th e m o u n ta in su m m e r, w ith som e o r m u c h d eclin e in d a ily p re c ip ita tio n . W h e n a re g io n a l s to r m “ m is s e s ” fro m la ck of w a te r, th e co n d itio n te n d s to b e se lf-re c tify in g , fo r a d d itio n a l in so la tio n received b y th e m o u n ta in reg io n d u r in g th e w h o lly c le a r d a y ac ce le ra tes m e ltin g of th e snow fields, w ith a re s u ltin g in ­ creased s u p p ly of w a te r to s tr e a m s flow ing in to th e p a r k . In th e e v e n t t h a t all th e m o u n ta in sn o w s a re m e lte d , as u su a lly occurs in m id s u m m e r on th e m a rg in s of th e S an L u is V alley

720

R onald

L.

[J- F. I.

Iv es.

a n d o f te n a r o u n d S o u th P a r k , o n ly m o is tu r e re c e iv e d fro m " o u t s i d e ” w ill r e v iv e t h e re g io n a l s to r m s . In te rfe re n c e B e tw e e n R e g io n a l S to r m s .— I t is c o m m o n ly b e ­ lie v e d in th e C o lo ra d o R o c k ie s t h a t t h e r e g io n a l s t o r m s a r e a sin g le s to r m , o c c u r r in g o v e r th e w h o le m o u n t a i n re g io n . T h is v ie w is q u ite lo g ic a l, a n d is s e e m in g ly s u p p o r te d b y field o b s e r v a tio n s u n til th e s to r m o v e r a s in g le p a r k " m i s s e s ” b e c a u s e of w a te r s h o r ta g e o r a n a n tic y c lo n e o v e r t h a t p a r k , w h ile s to r m s o v e r o t h e r p a r k s o c c u r w ith t h e i r n o r m a l in ­ te n s ity a t th e i r r e g u la r tim e of d a y . C lo se o b s e r v a tio n o f th e s to r m s in tw o a d j a c e n t p a r k s fro m th e d iv id e b e tw e e n th e m d is c lo s e s t h a t th e s to r m s o v e r F ig . M

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.

DENVER, AUGUS1 3, 1930

1

1

1

1

1

A u g u s t 3, 1935. ( D a ta fro m U . S. W e a th e r B u re a u .) T h e b a ro m e tr ic v a ria tio n s h e re sh o w n re fle c t t h e d is tu r b a n c e s in t h e m o u n ta in s , 40 m iles w est of D e n v e r , d u r in g th e re g io n a l s to rm s s h o w n in F ig s . 5, 6, a n d 7. A t t h e s a m e tim e , a n a n e rio d in th e m o u n ta in s (on A ra p a h o P e a k ) s h o w e d n o s u c h r e g u la r d ip a n d rise a s th is , b u t “ j i t t e r e d " r a p id ly u p a n d d o w n , p r o b a b ly a s a r e s u lt o f p u r e ly lo ca l a ir d is tu r b a n c e s . I n B o u ld e r, 30 m ile s n o r th w e s t of D e n v e r , t h e b a r o m e te r d e c lin e d a n d ro se s im ila rly to t h a t in D e n v e r, b u t th e m in o r h u m p s a n d h o llo w s in th e c u rv e , a tt r ib u t e d to lo cal d is tu r b a n c e s , w e re n o t id e n tic a l. D e n v e r

B a ro g ra p h

T ra c e ,

th e tw o p a r k s d o n o t n e c e s s a r ily " b r e a k ” a t e x a c t ly t h e sa m e tim e , a lth o u g h o n e u s u a lly d o e s n o t la g m o re t h a n h a lf a n h o u r b e h in d th e o th e r . I n te r f e r e n c e b e tw e e n s im u lta n e o u s o r n e a r ly s im u lta n e o u s r e g io n a l s to r m s in a d j a c e n t a r e a s a p p a r e n t l y d o e s n o t o c c u r, th e ris in g a i r c u r r e n ts a lo n g t h e p a r k w a lls e ff e c tiv e ly iso ­ la tin g th e m a in m a s s of c lo u d s o v e r o n e p a r k f ro m t h a t o v e r a n o th e r . I n th e d is t u r b e d zo n e , o v e r th e m o u n ta in r im s o f th e p a r k s , so m e m in g lin g o f s to r m c lo u d s d o e s t a k e p la c e , b u t th e v e r y fo rc e s t h a t c r e a te t h i s d is t u r b e d z o n e a ls o se em to is o la te i t e ffe c tiv e ly f ro m th e m a jo r c lo u d m a s s e s . A s lig h t " c a s c a d e e f f e c t” h a s b e e n n o te d in w e s t c e n tr a l C o lo ra d o , w h e re v a lle y s to r m s o n th e W e s te r n S lo p e " b r e a k ”

Dec., 1938.]

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C olorado

R o c k ie s .

721

ea rly in th e d a y , a n d so m e of th e ir " e s c a p e d ” clo u d s cre e p e a stw a rd a c ro ss th e ra n g e s to jo in th e re g io n a l clo u d m a sses o v er th e p a r k s . T h is m a y in c re a se th e m o is tu re su sp e n d e d o v er th e p a r k s b y a s m u c h a s o n e p e rc e n t, w h ich is a b o u t eq u a l to th e m o is tu re loss ca u se d b y th e " e s c a p e ” of reg io n a l sto rm clo u d s e a s tw a rd to w a r d th e p la in s. A e ria l S tr a tific a tio n .— I t is a p p a r e n t, fro m field o b s e rv a ­ tions, t h a t s to r m s of v a r io u s ty p e s a re co n fin ed to c e r ta in r a th e r d e fin ite a ltitu d e s . T h e re g io n a l clo u d m asses, w h ich ac c u m u la te m o is tu re fo r th e re g io n a l sto rm s , n o rm a lly o cc u r b etw een th e e le v a tio n s of 14,000 a n d 16,000 fe e t. A t th e se levels, te m p e r a tu r e s a re v e r y n e a r fre ez in g ev e n in su m m er, an d m a x im u m w in d v e lo c itie s a p p ro a c h 30 m iles a n h o u r. W in d d ire c tio n , w h ile n o t c o n s ta n t, is g e n e ra lly fro m th e w e st an d n o rth w e s t. B elow 14,000 fe e t, th e w in d s a re n o rm a lly th e v a g r a n t breezes of th e p a r k s , b lo w in g " e v e r y w h ich w a y ,” u s u a lly for no o b v io u s re a so n . I t is in th is zo n e— fro m th e g ro u n d surface to 14,000 f e e t— t h a t th e local o r v a lle y s to rm s o cc u r. A bove 16,000 f e e t is th e zone of " t r a d e w in d s ” w h ich ex te n d s u p w a rd to a t le a s t 18,000 fee t, a n d p r o b a b ly m u c h fa rth e r. C lo u d s in th is a ir s tr a t u m m o v e r a p id ly fro m w e st to ea st, o fte n a t v e lo c itie s ex c ee d in g 50 m iles p e r h o u r, as d e t e r ­ m ined b y " c lo c k in g ” c lo u d sh a d o w s. S e v e ra l w in d v elo cities of m o re th a n 150 m ile s a n h o u r in th is a ir s tr a t u m h a v e b een re p o rte d b y a v ia to r s , w h o " l e f t D e n v e r fo r S a lt L a k e a n d lan d ed fo r g as a t L im o n .” So f a r a s c a n b e d e te r m in e d , clo u d s h a v in g e le v a tio n s of 17,000 fe e t o r m o re h a v e n o effect on th e w e a th e r of th e m o u n ta in reg io n a n d a re n o t affec ted b y it, b u t sail se re n ely across th e s k y fro m w e st to e a s t w ith o u t e ith e r g a in in g o r losing m o is tu re . C y clo n es a n d a n tic y c lo n e s te n d to a lte r th e lev els of th e se a ir s tr a t a t e m p o r a r ily ; cy c lo n e s c a u sin g a dow m w ard w a rp in g , an tic y c lo n e s w a r p in g th e s t r a t a u p w a rd . E x p la n a to ry H y p o th e s is .— F ro m field o b s e rv a tio n s in th e C olorado R o c k ie s a n d fro m c u r r e n t th e o rie s of local a tm o s ­ p heric c irc u la tio n , a r a t h e r p la u sib le h y p o th e s is, e x p la in in g all of th e m a jo r f e a tu r e s of th e reg io n a l s to rm s, m a y b e b u ilt u p . T h is h y p o th e s is is h e re p re s e n te d w ith fu ll a w a re n e ss t h a t it

722

R onald

L.

Ives.

[J. F . I.

is b a s e d o n in c o m p le te in f o r m a tio n , a n d h e n c e m a y b e s u b je c t to so m e o r m u c h e r r o r. R e g io n a l s to r m s a r e c o n v e c tio n p h e n o m e n a , la r g e ly c o n ­ fin ed to a d e f in ite a r e a b y r is in g a ir c u r r e n t s a lo n g t h e w a lls o f th e b a s in of t h e i r o rig in , a n d d e p o s itin g m u c h o f th e ir p r e c ip ita tio n in th e s a m e g e n e ra l a r e a fro m w h ic h i t w a s o rig in a lly e v a p o r a te d . P re v a ilin g w in d s te n d to m a s s th e c lo u d s of a re g io n a l s to r m o n th e le e w a rd s id e of th e b a s in o f t h e i r o rig in , a n d to c a r r y so m e o r m u c h of th e e v a p o r a te d m o is tu r e a w a y f ro m th e b a s in . I n tim e s of n o r m a l b a r o m e tr ic p re s s u r e , c o n v e c tio n c a u se d b y su rfa c e h e a tin g in a p a r k c o n tin u e s u n til t h e h e a t s u p p ly c e a se s, e i th e r b e c a u s e of th e f o r m a tio n o f a la rg e c lo u d c o v e r o r of th e s e ttin g of th e s u n . H e a te d a ir, m o is te n e d b y e v a p o r a tio n , ris e s to a h e ig h t w h e re c o n d e n s a tio n ta k e s p la c e . T h is d e te r m in e s t h e b o tto m o f th e re g io n a l c lo u d s t r a t u m . T h e to p of th is c lo u d s t r a t u m s e e m s to b e d e t e r ­ m in e d b y th e b o tto m of t h e ‘'t r a d e w i n d ” s t r a t u m . A n y m o is t a i r r is in g in to th e ‘‘ tr a d e w i n d ” s t r a t u m is r a p id ly c a r rie d a w a y , in th e d ir e c tio n o f K a n s a s . W h e n e v e r th e h e i g h t of c o n d e n s a tio n is b e lo w t h e b a s e o f th e ‘‘tr a d e w i n d ” s t r a t u m , a re g io n a l c lo u d la y e r m a y fo rm . B e tw e e n th e b a s e a n d to p o f a re g io n a l c lo u d s t r a t u m , t h e n o r m a l v io le n t c u m u lu s c o n v e c tio n ta k e s p la c e . A s th e c lo u d c o v e r o v e r a p a r k th ic k e n s , b y g r a d u a l a c c r e ­ tio n of w a te r v a p o r , i t te n d s to r e fle c t m o re a n d m o r e o f th e s u n ’s r a d ia tio n b a c k in to s p a c e , b a r r in g i t fro m a c c e ss to th e g r o u n d , a n d e v e n tu a lly g r e a tly r e d u c in g lo c a l c o n v e c tio n . T h is is a c c o m p a n ie d b y a g e n e r a l c o o lin g o f a ll th e a i r f ro m c lo u d s to g r o u n d , a n d o f te n p r e c ip ita tio n o f th e m o is tu r e h eld s u s p e n d e d b y th e clo u d s. F a ilu r e o f th e re g io n a l s to r m c y c le t o c o m p le te its e lf w ith a r a in s t o r m d u r in g w e a th e r o f n o r m a l b a r o m e tr ic p r e s s u r e is d u e t o in s u ffic ie n t m o is tu re , a n d a lm o s t in v a r ia b le a c c o m ­ p a n ie s e i th e r d r o u g h t o r fre e z in g in th e p a r k s . C o m p a r in g field o b s e r v a tio n s a n d th e o r ie s s till f a r th e r , a b n o r m a l c o n d itio n s m a y b e h y p o th e c a te d , a n d c o m p a re d w ith o b s e rv e d o c c u rre n c e s .

Dec., 1938.]

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723

A bnorm ally low u p p e r a ir te m p e ra tu re s, ab n o rm ally low barom etric p ressure, a n d a b n o rm a lly large am o u n ts of av a il­ able m oisture o n th e g ro u n d , all te n d to lower th e base of th e regional cloud s tra tu m to o r below th e rim s of th e p a rk w alls. These co n d itio n s in h ib it w e st-e a st m o istu re m igration by re ­ taining th e clouds in th e p ark s. T h is leads to a v e ry w et sum m er in th e m o u n ta in s, accom panied b y d ro u g h t on the high plains. T h e su m m er of 1936, w hen it rained for m ore th an three h o u rs on 80 of th e 84 d a y s sp e n t in the field F ig .

C louds

in

E a stern

M id d l e

10.

Park

D u r in g

a n

A n t ic y c l o n e .

P h o to g ra p h e d fro m t h e m ain s tr e e t of G ra n b y , C o lo rad o , n e a r th e ju n c tio n of th e C olorado a nd F ra se r R iv ers, th e s e clo u d s, a s so c ia te d w ith th e v a lle y s to rm s, b u t lifted sev eral h u n d red feet above th eir no rm al e le v a tio n s b y a v a lle y b reeze, c o m p le te ly h ide th e F ro n t R an g e (Fig, 1, n u m b er 10), a lth o u g h th e to p of th e h ig h est clo u d is o n ly a b o u t 12,000 fe e t a b o v e se a level, w hile th e crest of th e range h e re a v e ra g e s o v e r 13,000 fe e t. A t th is tim e th e ty p ic a l regional clo u d s tra tu m was a bsent, due to a n a n tic y c lo n e o v e r th e m o u n ta in region.

(ea stern M id d le P a r k ) , is ty p ic a l of a w e t m o u n ta in su m m er. D u s t s to rm s on th e p la in s a tte s te d to th e d ro u g h t th e re . T h is w o u ld su g g e s t t h a t th e su p p o se d in v e rse re la tio n of m o u n ta in to p la in s ra in fa ll is so m e th in g m o re th a n m e re ru ra l g u e s stim a tio n . ’’ D u rin g a w e t m o u n ta in su m m e r, m o s t of th e few g la c ie rs now p re s e n t in th e h ig h c irq u e s g a in a few th o u s a n d to n s of ice, an d m a n y of th e sn o w field s do n o t m e lt a w a y as ra p id ly as usual. I t w o u ld seem , fro m th is, t h a t a d e p re ssio n of th e regional clo u d s t r a t u m b y o n ly a few h u n d re d fee t, a s now

R onald

L.

I ves.

[J . F . I.

o c c u rs fro m tim e to tim e , w o u ld , if c o n tin u e d fo r a n u m b e r of su c c e ssiv e s u m m e r s , b r in g a b o u t a m in o r ice a g e in th e m o u n ta in s , p e r h a p s o f a s g r e a t a m a g n itu d e a s t h e s m a ll p o s t- la te s t- W is c o n s in ice a d v a n c e n o te d in th is a r e a . 11 A b n o rm a lly w a r m u p p e r a ir, a b n o r m a lly h ig h b a r o m e tr ic p re s s u re , a n d d r o u g h t in th e p a r k s , te n d to r a is e th e le v e l of t h e re g io n a l c lo u d s t r a t u m , o r s u p p r e s s i t a l to g e t h e r , d u e to th e m ix in g of r is in g a i r f ro m th e p a r k s w ith th e a i r o f th e “ tr a d e w i n d ” s t r a t u m . T h e s e c o n d itio n s a s s is t w e s t- e a s t m o is tu r e m ig r a tio n , le a d in g to e x tr e m e d e s s ic a tio n o f th e p a r k s , r a p id m e ltin g of th e m o u n ta in s n o w fie ld s a n d g la c ie rs , a n d m a k e m o re m o is tu r e a v a ila b le fo r p r e c ip ita tio n so m e w h e re e a s t o f t h e m o u n ta in s . N o e x tre m e c a se of t h is h a s b e e n o b s e rv e d , n o r d o th e w e a th e r r e c o rd s o r o ld t i m e r ’s t a le s te ll o f s u c h h a p p e n in g s . I t se e m s p r o b a b le t h a t m ild s u p p r e s s io n o f th e r e g io n a l s to r m s h a s ta k e n p la c e d u r in g p e r io d s o f a b n o r m a l r a in f a ll o n th e p la in s , b u t t h a t se v e re c a se s h a v e n o t o c c u r re d sin c e th e c o m in g o f th e w h ite m a n to N o r t h A m e ric a . T h e o r e tic a lly , a t le a s t, a s u m m e r of t h is k in d w o u ld le a d t o e x tr e m e g la c ia l m e ltin g , if n o t to th e e x tin c tio n o f m a n y o f t h e s m a ll m o u n ta in g la c ie rs . O b s e r v a tio n s o f th e a n n u a l la y e r s in F a i r G la c ie r 12 s u g ­ g e s t t h a t p e r io d s of e x tre m e m e ltin g a r e n o t f r e q u e n t, th e re b e in g o n ly th r e e “ b r e a k s ” in a s e rie s of m o re t h a n 400 a n n u a l ice b a n d s . H o w m a n y y e a r s a r e r e p r e s e n te d b y th e s e u n c o n f o r m itie s in th e s tr a tif ie d ice h a s n o t b e e n d e te r m in e d , a n d a s a n o t h e r u n c o n f o r m ity s e e m s to b e in t h e m a k in g a t p r e s e n t, c o n c lu s io n s a s to p a s t c lim a te , d r a w n f ro m th e ice b a n d re c o rd , m a y b e of li t t l e v a lu e . G la c ia l r e c o rd s d o n o t re v e a l th e sp e e d o f m e ltin g , b u t o n ly t h a t m e ltin g in ex cess of th e a n n u a l a c c r e tio n to o k p la c e . V alley Sto rm s.

V a lle y s to r m s , s e c u rin g th e m a jo r p a r t o f t h e i r m o is tu re f ro m th e s a m e v a lle y in to w h ic h th e y l a t e r p r e c ip ita te it, a n d ta k in g p la c e w h o lly w ith in t h a t v a lle y , a r e lo c a l p h e n o m e n a w h ic h a r e r e p e a te d m a n y tim e s in th e C o lo ra d o R o c k ie s . I n t h is a r e a , a -m a x im u m of f o u r re g io n a l s to r m s c a n ta k e p la c e a t o n e tim e . N o m o re a r e p o s s ib le . . . th e r e a r e o n ly

D ec., 1938.]

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four major parks. In contrast, there are more than 500 valleys in the Colorado Rockies that could, at least theo­ retically, contain simultaneous local storms, and probably more than 200 of these valleys actually do have a daily storm within their confines during part or all of the mountain summer. F ig . 11.

TOPOGRAPHIC .MAP OF THE MONARCH V M 1 E Y AND VICINITY GRAND COUNTY, COLORADO

M a p

o f

t h e

M onarch

V alley, G rand

C ounty,

C olorado.

( D a ta fro m field n o te s a n d U . S. G . S. R o c k y M o u n ta in N a tio n a l P a rk Q u adrangle.) From th e C o lorado R iv e r to M o n a rc h L a k e a re th e “ fla ts,’* once th e m eltin g b asin of th e Pleistocene glaciers t h a t c a rv e d th e v a lle y . A b o v e M o n a rc h L a k e , to a b o u t th e 10,000 fo o t contour, a re th e t r ib u ta r y v a lle y s, a n d fro m th e 10,000 fo o t c o n to u r to th e c re s t of th e ran g e are the cirques, in w hich a re still p re s e n t m o rib u n d re m e n e n ta l g laciers. M o n a rc h V alley sto rm s, in general, do n o t cross t h e w a te rs h e d o u tlin e o n th is m ap e x c e p t to th e e a st, a n d in g e n eral, th e to p lim it of v alley sto rm d istu rb a n c e s is n o t m o re th a n 1,500 fe e t a b o v e th e v a lle y floor, ex c ep t in th e cirques, w here v e rtic a l a ir c u rre n ts c a rr y sto rm clo u d s to a c o n sid erab le h e ig h t. T h e m o st rap id evaporation, in th is v a lle y , o ccu rs in th e “ w e t m e a d o w s ’' b elow th e 8,250 fo o t c o n to u r. T h e m ost violent p rec ip ita tio n , fro m th e v a lle y s to rm s, o ccu rs ab o v e th e 10,250 fo o t c o n to u r on b o th sides of the range, a n d below 13,000 fee t.

T h e se v a lle y s to r m s a re d is t in c t fro m th e re g io n a l sto rm s, ta k in g p la ce in a lo w e r a ir s tr a t u m , a n d w h ile la rg e ly cau se d by co n v e ctio n , th e y c a n ta k e p la c e w h e n th e reg io n a l s to rm s are su p p re sse d b y a n a n tic y c lo n e , a n d d o n o t, in g en e ral, in te rfe re e ith e r w ith e a c h o th e r o r w ith th e reg io n a l sto rm s,

726

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e x c e p t a t th e e x tr e m e h e a d s o f t h e i r v a lle y s , d u r in g th e p e rio d of m a x im u m c lo u d tu r b u le n c e . M o re t h a n f ifty v a lle y s c o n t a in i n g s to r m s of th is t y p e h a v e b e e n n o te d b y t h e w r i te r in v a r io u s p a r t s o f C o lo ra d o , a n d in o th e r p a r t s of t h e s t a t e m a n y m o re s to r m a r e a s h a v e b e e n r e p o r te d b y s k ille d o b s e rv e rs ( m o s tly U . S . G e o lo g ic a l S u rv e y m e n ). T h e s e s to r m s a r e a ll q u i t e s im ila r in o p e r a tio n , a n d a f te r a few d a y s of o b s e r v a tio n , t h e a c tio n s o f t h e s to r m in a n y ty p ic a l v a lle y c a n b e p r e d ic te d w ith a g r a ti f y in g d e g re e of su c c e ss. I n th e M o n a r c h V a lle y , G r a n d C o u n ty , C o lo ra d o , o n th e e a s te r n e d g e o f M id d le P a r k (F ig s . I , n ) , m o re t h a n 100 of th e s e s to r m s w e re o b s e rv e d d u r in g t h e s u m m e r s of 1932—1936 in c lu s iv e , a n d th is v a lle y w ill b e t a k e n a s t h e ty p e a r e a , e v e n th o u g h e x te n d e d o b s e r v a tio n s o f lo c a l s to r m s m a y s h o w th o s e of t h is a r e a to b e v e r y s lig h tly a t y p ic a l. T y p ic a l V a lle y S to r m .— A ty p ic a l v a l le y s to r m b e g in s s h o r tly a f te r s u n u p , w ith a r a t h e r r a p id r e p la c e m e n t o f th e e a r ly m o r n in g g r o u n d h a z e b y a s t r a t u m of s h im m e r in g h u m id a i r t h a t r a p id l y th ic k e n s u n til i t fills t h e lo w e r r e a c h e s of th e v a lle y fro m floor to r im . A n y o f t h is a l m o s t- s a tu r a te d a i r t h a t ris e s a b o v e th e v a lle y r im is im m e d ia te ly s w e p t a w a y b y th e p a r k - w a ll c o n v e c tio n c u r r e n ts a s s o c ia te d w ith th e re g io n a l s to r m s . A ir c u r r e n ts b e g in to ris e fro m th e b o tto m s of th e c irq u e s a t th e h e a d s of th e v a r io u s m in o r t r i b u t a r y v a lle y s a b o u t h a lf a n h o u r a f te r s u n lig h t f ir s t r e a c h e s c ir q u e flo o rs, a n d s h o r tly a f t e r n o o n , th e e n t ir e v a lle y s y s te m b e g in s to " d r a w ” lik e a c h im n e y . V e r y h u m id w a r m a i r m o v e s s lo w ly u p v a lle y (5 -1 0 m .p .h .) fro m th e f la ts t o th e c irq u e s , m a r k e d ly ra is in g te m p e r a t u r e s a n d h u m id itie s d u r in g t h e la te m o rn in g a n d e a r ly a f te r n o o n . V a lle y a ir, d u r in g t h i s tim e , is a lm o s t s a t u r a t e d . S w e a t d o e s n o t e v a p o r a te , m o is tu r e c o n d e n s e s on e v e r y th in g co o l ( p a r tic u la r ly in s id e in s t r u m e n ts a n d le n s c o m b in a tio n s ) a n d th e a ir is o p p r e s s iv e . D u r in g th e s e m id ­ d a y h o u rs , m o u n ta in e e r s o f te n e x p e rie n c e a r a t h e r a c u te e x h a u s tio n , a c o n d itio n a lm o s t id e n tic a l w ith " g l a c i e r la s si­ t u d e , ” w h ic h m a y h a v e a s im ila r c a u s e . C lo u d f o r m a tio n b e g in s o v e r th e c irq u e s in la te m o r n in g w ith te n u o u s a n d e p h e m e ra l w is p s t h a t b e c o m e la r g e r a n d

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m ore la s tin g a s th e d a y p ro g re sses. D u rin g th e e a rly a f te r ­ noon, d e fin ite a n d s o m e w h a t la s tin g c u m u li fo rm o v e r th e cirq u es a t e le v a tio n s n e a r 13,000 fee t, a n d slo w ly d r if t e a s t­ w ard, risin g s lig h tly a s th e y e n c o u n te r cirq u e -w a ll “ c h im n e y c u r re n ts .” I t sh o u ld b e d e fin ite ly n o te d t h a t th e se c u m u li are in n o v isib le w a y r e la te d to th o se of th e re g io n a l s to rm s th a t form m o re th a n 1,000 fe e t h ig h e r (F ig . 15). F ig . 12.

T he

M onarch

V alley

in

M id m o r n in g .

W ith th e c a m e ra p o in tin g s o u th e a s t, th is p h o to g ra p h w as ta k e n fro m th e n o rth late ra l m oraine (Fig. 11, sect. 8, T 2 N , R 75 W ) of th e g lacier t h a t e x c av a te d a n d fo rm e rly filled th e v alley . A l­ though p a n c h ro m a tic film a n d a d e e p y ellow filter w ere u sed , th e m o u n ta in s, fo u rte e n m iles from the cam era, a re p a rtly o b sc u re d b y e v a p o ra tio n h a z e. In th e low er rig h t a re th e “ w e t m ea d o w s’* from w hich in ten se e v a p o ra tio n ta k e s p lace, a n d in to w h ich th e e n tire v alley sy ste m d rain s. O n th e horizon are th e reg io n a l s to rm clo u d s, a n d in th e m iddle d ista n c e a re th e shad o w s of o th ers. M id ­ m orning co n d itio n s on a “ n o r m a l” d a y a re h e re sh ow n.

O v er e a c h c irq u e , in g e n e ra l, o n ly on e c u m u lu s form s. T h e tim e of fo rm a tio n of th e c u m u lu s is slig h tly d iffe re n t for each c irq u e o f a v a lle y s y s te m , a n d th e tim e of m a x im u m cloudiness o v e r a d ja c e n t v a lle y s y s te m s is n o t n e c e ssa rily th e sam e, a lth o u g h m a x im u m c lo u d in e ss is se ld o m re a c h e d e a rlie r th a n n o o n , o r l a te r th a n five in th e a fte rn o o n .

728

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W h ile th e c u m u li a r e f o rm in g o v e r th e c irq u e s , d e f in ite a ir c u r r e n ts a r e e s ta b lis h e d in th e v a lle y s . T h o s e f ro m t h e f la ts to th e c irq u e s fo llo w p a t h s a few h u n d r e d f e e t a b o v e th e v a lle y flo o rs, a n d h a v in g a b o u t th e s a m e g r a d i e n t ( m in o r b u m p s a n d h o llo w s in th e v a lle y flo o r h a v e n o d e t e c ta b l e e ffe c t o n th e m o v in g a ir ) . T h o s e n e a r th e c ir q u e h e a d w a lls a r e a lm o s t v e r tic a l. T h e tr a n s i t i o n fro m v a lle y to “ c h i m n e y ” c u r r e n ts is v e r y s h a r p , o f te n ta k in g p la c e w ith in a few h u n d r e d f e e t. J u s t b e fo re th e v a lle y s to r m b r e a k s , th e r e is a v e r y p r o ­ n o u n c e d c o o lin g o f th e v a l le y a ir, a n d a d o w n w a r d e x te n s io n o f th e c u m u li in to th e c irq u e s to w ith in a few r o d s o f th e c irq u e floors. V io le n t a i r c u r r e n ts c a r r y d u s t, tw ig s, le a v e s, a n d s o m e tim e s r o c k fla k e s fro m th e v a l le y flo o r a n d w a lls u p in to th e c u m u lu s . W h is tlin g , h is s in g , a n d r o a r in g s o u n d s , c a u se d b y t h e r a p id p a s s a g e of t h e w in d o v e r s h a r p ro c k s , a n d a low p itc h e d “ f l u tte r i n g ,” a c c o m p a n y t h is p h a s e o f th e s to r m . S u d d e n ly , all s o u n d s s to p . U s u a lly t h e s ile n c e , w h ic h m a y la s t fo r a d o z e n se c o n d s, is b r o k e n b y a s h a r p th u n d e r c la p , a n d fo llo w e d a few se c o n d s l a t e r b y a v io le n t d o w n p o u r. A s th e p r e c ip ita tio n b e g in s, th e v a lle y a i r c u r r e n t s r u s h to w a r d th e c irq u e s , c lo u d s m a te r ia liz e s u d d e n ly in th e t r i b u t a r y v a lle y s , a n d ra c e u p w a r d to w a r d t h e m a in c u m u lu s in a n d o v e r th e c irq u e a t th e h e a d o f e a c h t r i b u t a r y , in c re a s in g in size a s th e y tr a v e l. C lo u d w r a ith s s tr e a m e a s tw a r d th r o u g h g a p s in t h e ra n g e a t th e v a lle y h e a d s , r e fo rm in to c u m u li o n th e e a s te r n slo p e, a n d , to s s e d v io le n tly a b o u t b y th e “ c h im n e y c u r r e n t s ” s p r e a d r a in a n d h a il o v e r a m ile -w id e z o n e p a r a lle l to th e ra n g e c r e s t. A few s m a ll c u m u li m a y c ro s s th e r a n g e in f a v o r a b le lo c a tio n s , b u t u s u a lly th e s e a r e b a d l y to r n b y u p r u s h in g a ir c u r r e n ts b e fo re t h e y h a v e tr a v e lle d m a n y r o d s b e y o n d th e r a n g e c r e s t. H a ils to n e s , u s u a lly less t h a n 3 / 4 " in d ia m e te r , b u t o c c a ­ s io n a lly a s la rg e a s 2 “ ( m e a s u r e d ) , a r e c o m m o n ly p r e c ip ita te d f ro m c lo u d s o f v a lle y s to r m s t h a t h a v e c ro s s e d a d iv id e , b u t a r e se ld o m o b s e rv e d in p r e c ip ita tio n f r o m c lo u d s s till o v e r th e c irq u e in w h ic h th e y f o rm e d . C le a rin g o f th e a ir a f t e r a v a l le y s to r m is q u ite p r o m p t, u s u a lly ta k in g o n ly t h i r t y m in u t e s o r so, r e g a r d le s s o f th e

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a tm o sp h e ric c o n d itio n s a b o v e 14,000 fee t. T w o ra in -s to rm s in th e sa m e a f te rn o o n , c a u s e d b y th e b re a k in g of o n e ty p e of sto rm a f te r th e c le a rin g fo llo w in g a n o th e r , a re o fte n n o te d in th e v a lle y s. W h e n th e v a lle y s to r m b r e a k s m u c h b efo re th e regional sto rm , th e v a lle y a ir, in la te a fte rn o o n , w ill clea r, th e n la te r “ fog u p ” a s a r e s u lt of reg io n a l s to rm p re c ip ita tio n . If, on th e o th e r h a n d , th e re g io n a l s to rm b re a k s first, th e re will b e v io le n t r a in s a n d b r ig h t su n sh in e d u rin g th e v a lle y sto rm . V alley s to r m s in th e M o n a rc h V alley b eg in a s e a rly in th e y e a r as th e re is w a te r in th e “ w e t m e a d o w s ,” a n d c o n tin u e to be an a lm o s t-d a ily o c c u rre n c e u n til th e “ w e t m e a d o w s ” are F i g . 13. W est

VALLEY F L O O R

/

P r o f il e

o f

t h e

M onarch

V alley.

D a ta for th is figure w ere o b ta in e d fro m th e U. S. Geological S u rv e y m ap of th e a re a (som e­ w hat generalized), a n d from clo u d o b se rv a tio n s. V ertic a l in te rv a ls a re th o u sa n d s of feet, hori­ zontal in terv als a re m iles. I t sh o u ld b e n o te d t h a t th e local sto rm zone, ro u g h ly confined to th e trib u ta ry valleys a n d cirq u e s, e x te n d s u p w a rd in to th e reg io n al sto rm cloud s tr a tu m n e a r th e cirques, causing, in th is a re a , in te rfe re n c e b e tw e e n sto rm s w h en ev er th ey a re n e a rly o r ex actly sim ultaneous.

covered w ith ice, o r th e w a te r a v a ila b le fo r e v a p o ra tio n fro m th em is g r e a tly le ssen e d b y d r o u g h t. T h e se aso n u s u a lly la sts a b o u t 160 d a y s , d u r in g w h ic h tim e th e re a re a b o u t 125 v a lle y storm s, n o t all of th e m se v ere. O th e r v a lle y s , in d iffe re n t ranges, o r h a v in g d if fe r e n t ex p o su re s o r p o te n tia l w a te r supplies, h a v e se a so n s of g r e a te r o r le sser le n g th . E ffect o f C yclones a n d A n tic y c lo n e s .— C y c lo n e s h a v e a definite, b u t n o t e a sily d e te r m in a b le effect on v a lle y sto rm s, as th e y te n d to “ te le s c o p e ” th e se v e ra l c o n d e n sa tio n levels in to one, m a k in g s e p a r a tio n of s to r m c o m p o n e n ts d ifficu lt o r im possible. In g e n e ra l, th e p r e c ip ita tio n in a v a lle y is less v io le n t a n d m o re la s tin g d u rin g a cy c lo n e , w ith s m a lle r r a in ­

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d r o p s , less th u n d e r a n d lig h tn in g , a n d p r a c tic a lly n o h a il. T h is g e n e r a liz a tio n fa lls d o w n in t h e e v e n t t h a t t h e c y c lo n e b r in g s a s u m m e r b liz z a rd , w h e n a lm o s t a n y t h in g m a y b e e x p e c te d . W i th th e c o m in g o f a c y c lo n e to th e m o u n ta in re g io n , i t se e m s m o re lo g ic a l to lu m p th e lo c a l a n d re g io n a l s to r m s a s a sin g le lo c a l f a c to r t h a n to t r y to c o n s id e r th e m , a n d th e ir e ffe c t in th e c y c lo n e , s e p a r a te ly . A n tic y c lo n e s , w h ile s u p p r e s s in g r e g io n a l s to r m s , h a v e a r a t h e r s lig h t e ffe c t o n th e v a lle y s to r m s . D u r i n g th e f ir s t d a y o f a n a n tic y c lo n e , th e le v e l of c o n d e n s a tio n o f t h e v a lle y a ir is r a is e d , p e r m i ttin g th e v a lle y s to r m c u m u li to d r i f t a c ro ss d iv id e s w ith less f r a g m e n t a ti o n . T h e e v a p o r a tio n in th e w e t m e a d o w s is s o m e w h a t g r e a te r , b e c a u s e o f th e w a r m e r a i r a n d c le a r e r sk y , a n d t h e t o t a l p r e c ip ita tio n fro m th e v a lle y s to r m s is s lig h tly in c re a s e d , a s a r e s u lt. T h e p r e c ip ita tio n o n a g iv e n a r e a r e m a in s a b o u t th e s a m e , w h e th e r o r n o t a n a n t i ­ c y c lo n e is o v e r th e m o u n ta in s , b u t th e a r e a r a in e d o n is v e r y m u c h g r e a t e r d u r in g a n a n tic y c lo n e . H a il is le ss c o m m o n d u r in g th e f irs t d a y o f a n a n tic y c lo n e t h a n a t o t h e r tim e s . A f t e r th e f ir s t d a y , c lo u d le v e ls a n d o t h e r f e a tu r e s of th e v a lle y s to r m s s lo w ly r e v e r t to n o r m a l. T o p o g ra p h ic F a cto rs.— W i t h o u t th e s te e p - w a lle d g la c ia te d v a lle y s , i t is d o u b tf u l w h e th e r t h i s t y p e o f s to r m c o u ld ta k e p la c e in th e R o c k y M o u n ta in re g io n , f o r th e e x is te n c e o f th e s e s to r m s se e m s to d e p e n d u p o n to p o g r a p h ic f e a tu r e s t h a t a re n o r m a lly c a u s e d o n ly b y m o u n ta in g la c ia tio n . W h ile n o e x a c t c o m p a r is o n s of v a lle y s a r e p o s s ib le b e c a u s e o f t h e g r e a t to p o g r a p h ic d iffe re n c e b e tw e e n th e m , v a lle y s y s te m s h a v in g th e s te e p e s t g r a d ie n ts , t h e m o s t a b r u p t c ir q u e w a lls , th e la r g e s t m e ltin g b a s in s , a n d t h e n a r r o w e s t t r i b u t a r y v a lle y s , se e m to h a v e th e m o s t v io le n t s to r m s . R a t h e r s tr a n g e ly , w h ile r e la tiv e ly s t r a i g h t v a lle y t r e n d s s h o u ld in c re a s e th e v e lo c ity o f th e a ir c u r r e n ts , a n d h e n c e t h e v io le n c e o f th e s to r m s , th e r e se e m s to b e l i t t l e o r n o d iffe re n c e b e tw e e n th o s e in s t r a i g h t a n d c ro o k e d v a lle y s , a ll o t h e r th in g s b e in g a p p r o x i­ m a te l y e q u a l. T h e tr e n d o f th e v a lle y w ith re f e r e n c e to th e p r e v a ilin g w in d s se e m s to b e a n i m p o r t a n t f a c to r g o v e r n in g t h e v io le n c e of th e v a lle y s to r m s . V a lle y s o n t h e w in d w a r d sid e o f a ra n g e , in g e n e ra l, h a v e m o re r e g u la r a n d m o r e v io le n t s to r m s

Dec., 1938.]

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than those cut into leeward slopes. The prevailing winds seem to reenforce the rising air currents in windward-facing valleys, and to oppose those in leeward-facing valleys. Adequate shelter, such as a half-mile-high cliff, at the head of a leeward-facing valley seems to reduce the inhibitory effect of the prevailing winds on the valley storms. Absence or small size of the melting basin of the glacier that cut and once occupied the valley, or better-than-average drainage of that basin, is a definite inhibitor of valley storms. Theoretically, a steep-walled melting basin should be less effective in storm production than one with more-gentlysloping walls, but as no observed melting basin has walls so steep that they cast a shadow on the wet meadows within it for any length of time, that factor is probably negligible. The mathematical possibilities of these various relations are intriguing, and a series of very complicated and impressivelooking equations, that should explain everything, can be set up. Their only fault is that the answers, unless a “ boogie factor” is somewhere inserted into the calculations, bear no relation to observed occurrences. It seems probable that present field data and theories are too qualitative to justify mathematical treatment of the problem. Year-to-year Variations .— Variations in the intensity and timing of the valley storms from year to year have been noted both by the writer and by “ old tim ers” in the moun­ tains. In general, since 1934, the regularity of the storms has been somewhat disturbed, their precipitation has been largely concentrated on the western slopes, and more snow has accompanied them than was usual in the past. These con­ ditions are similar to what would be expected if a mild cyclone settled over the mountain region. From a time before the coming of the oldest now-living mountain residents until 1934, storms in many valleys occurred with such regularity that they were named the “ two o’clock rains,” or given some similar title suggestive of clock­ like regularity. Probably these storms have been disturbed, in the last few years, by the same occurrences that have upset the timing of the regional storms; probably a slight chilling of the upper atmosphere. Whether or not they will resume their regular periodicity in a few years remains to VOL. 226, NO. 1 3 5 6 ----51

73 2

R onald

L.

[J. F. I.

I v es.

F ig . 14.

V alley

Storm

C lou ds

R is in g

in

a

C ir q u e .

T h is p h o to g ra p h w a s ta k e n fro m t h e s u m m it r id g e of L o n e E a g le P e a k (ca . 1 2 ,6 0 0 ') in th e C r a te r L a k e H e llh o le , b e tw e e n C r a te r L a k e a n d F a ir G la c ie r (F ig . 11) in m id a f te r n o o n . T h e risin g a ir c u r r e n ts h e re , a p a r t o f th e c u m u lu s c o n v e c tio n , w e re q u ite v io le n t, a n d " f l u t t e r e d ” a u d ib ly as th e y b lew p a s t t h e s h a rp e d g e s o f t h e r o c k s . T h is a re a , o n e o f t h e c irq u e s a t t h e h e a d o f C ascad e C a n y o n , h a s a ra in fa ll e s tim a te d (fro m p r e c ip ita tio n a re a a n d o u tflo w ) a t n e a rly 100 in c h e s d u rin g t h e s u m m e r. P a r ts of t h e v a lle y o n ly a m ile d o w n s tre a m re c e iv e less t h a n o n e q u a r t e r a s m u ch . In e le v e n v is its t o C r a te r L a k e , e a c h la s tin g 24 h o u rs o r m o re , o n ly fo u r h o u rs of " g o o d p h o to g ra p h ic w e a t h e r ” w e re e x p e rie n c e d .

D ec., 1938-]

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733

be seen. So fa r a s c a n b e d e te rm in e d , th e re is n o sim p le re la tio n b e tw e e n s u n s p o t cycles, o r o th e r n a tu r a l r h y th m s , an d th is d is tu rb a n c e of th e v a lle y s to rm s. V aria tio n s in a S in g le S e a s o n .— L ik e th e reg io n a l sto rm s, th e v a lle y s to r m s te n d to d e c re a s e in in te n s ity s im u lta n e o u s ly w ith th e o b se rv e d la te s u m m e r d e c re a se in in so la tio n an d w a te r su p p ly . L ess h e a t a n d less w a te r d ec rease p ossible e v a p o ra tio n , a n d h e n c e c o n s id e ra b ly lessen p o te n tia l p r e c ip ita ­ tio n fro m c lo u d s of lo cal o rig in . T h e r e la tiv e d ec lin e in rain fall fro m th e v a lle y s to r m s is g r e a te r th a n t h a t of e ith e r in so latio n o r m o is tu re a v a ila b le fo r e v a p o r a tio n . U n lik e th e regional sto rm s , th e v a lle y s to r m s se ld o m d ie o u t a lto g e th e r u n til th e m e ltin g b a sin s, th e ir so u rc e of m o is tu re , a re e ith e r co m p letely d r y o r fro z e n o v e r. E x c e p t in th e S an L u is V alley, c o m p le te d e s s ic a tio n of a m e ltin g b a s in is e x c e p tio n a l, even w h en th e p a r k s su ffe r fro m v e r y se v ere d ro u g h t. In v a rio u s p a r ts of C o lo ra d o , th e v a lle y s to rm s b eg in to decline in in te n s ity a t d iffe re n t tim e s, a s m ig h t b e ex p e c te d from d ifferen ces in in itia l w a te r su p p ly , d ra in a g e , a n d c lim a te . S to rm s in v a lle y s t r i b u t a r y to th e S a n L u is V alley d eclin e in in te n sity a n d s o m e tim e s d ie o u t a lto g e th e r b efo re th e en d of Ju n e . In a few v a lle y s in th e s o u th w e s te rn S an J u a n M o u n ­ ta in s (F ig. 1, n u m b e r 17) th e s to r m s cease fro m la c k of m o istu re in m id - J u ly . A m a rk e d d ec lin e in th e p r e c ip ita tio n from th e s to rm s in a n y v a lle y m a y be e x p e c te d soon a f te r th e snow fields in th e c irq u e s h a v e m e lte d aw a y , a n d a f u r th e r decline o r c o m p le te c e s s a tio n sh o u ld follow so m e w eek s la te r, w hen th e m e ltin g b a s in d rie s u p . H o w ev er, th e tim e fro m th e v a n is h m e n t of th e sn o w field s u n til th e firs t good freeze is u su a lly to o s h o r t to p e r m it c o m p le te d ry in g of th e w e t m eadow s in th e m e ltin g b a sin . B arom etric E ffe c ts .— I t is n o t possible, fro m a v a ila b le d a ta , to d e fin ite ly d iffe re n tia te b e tw e e n th e b a ro m e tric c o m p o n e n ts of th e v a lle y a n d re g io n a l s to rm s . T h e tw o to g e th e r, h o w ­ ever, h a v e a v e r y d e fin ite e ffec t on b a r o m e te r s in th e m o u n ­ ta in s, a n d in tr o d u c e e a sily re c o g n iz a b le b u m p s a n d h o llo w s in to th e b a ro g r a p h tr a c e s of s ta tio n s on th e p la in s n e a r th e m o u n ta in s. I t w as o rig in a lly p la n n e d to s e p a r a te th e se c o m p o n e n ts b y co m p ariso n s of p la in s s ta tio n b a ro g r a p h tra c e s. T h o s e v a ria -

734

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F ig . 15.

C um ulu s

H a n g in g

o v e r

a

C ir q u e .

T h is c u m u lu s h a s i ts o rig in in a n d o v e r t h e C r a te r L a k e C irq u e ( F ig . 11), a n d is h a n g in g b e ­ tw e e n 13.000 a n d .I4.SOO fe e t. S h o r tly a f t e r th is p ic tu r e w a s ta k e n , t h e c lo u d d r if te d e a s tw a rd , e n s h ro u d in g N a v a jo P e a k o n t h e h o riz o n in th is p ic tu r e , a n d tr a v e le d o v e r t h e A lb io n a n d Isa b e lle V alleys, s p re a d in g r a in a n d h a il o v e r s e v e ra l s q u a re m ile s o n t h e e a s t e r n fla n k o f t h e F r o n t R a n g e (se e a lso F ig . 1 6 ). F o r e g ro u n d s h a d o w s a re th o s e o f c lo u d s d r if tin g a c ro s s t h e r a n g e f ro m W h e e le r

D ec., 1938.]

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735

tio n s o c c u rrin g o n d a y s w h e n no c y c lo n e s o r a n tic y c lo n e s w ere o v er th e m o u n ta in re g io n sh o u ld b e of m o u n ta in o rig in , a n d ch a n g es sh o w n o n ly o n o n e o r tw o tr a c e s sh o u ld b e of e x ­ tre m e ly local, a n d h e n c e of v a lle y s to rm , o rig in . A n u m b e r of such c o m p a ris o n s w e re m a d e , a n d th e re s u lts fo u n d a b s o ­ lu te ly in c o n c lu siv e . I t seem s p ro b a b le t h a t a n a d d itio n a l trace, fro m a p la in s s ta tio n f a r fro m th e m o u n ta in s , is n ee d ed , so t h a t c o m p o n e n ts of p u r e ly p la in s o rig in c a n b e e lim in a te d before s e a rc h fo r m o u n ta in c o m p o n e n ts is b e g u n . In g en e ral, a v io le n t re g io n a l sto rm , o r g ro u p of th e m , p ro d u ces a c h a r a c te r is tic “ b a t te r e d sin e w a v e ” b a ro g ra p h tra c e o v e r w id e a r e a s (F ig . 9). M ild e r re g io n a l s to rm s m a y o r m a y n o t p ro d u c e e a sily re c o g n iz a b le b u m p s a n d hollow s in p la in s b a r o g r a p h tra c e s . C lose to th e m o u n ta in s (in B o u ld e r, fo r e x a m p le ), e a ch n e a rb y v a lle y s to r m p ro d u c e s its o w n d e fin ite “ d i p ” in th e b a ro g ra p h tr a c e , c a u s in g a s te p lik e d e c lin in g tr a c e o n m a n y su m m er a f te rn o o n s (F ig . 17). I t is o fte n p o ssib le to go o u t to a p o in t on th e p la in s a b o u t 30 m iles fro m th e c r e s t of th e ra n g e a n d w a tc h th e sto rm s, th e n w a it a few m in u te s a n d o b se rv e th e “ d ip p in g ” of th e b a ro m e te r t h a t in th e m o u n ta in s sh o u ld th e o re tic a lly a c c o m ­ p a n y th e b re a k in g of th e s to rm s . F ro m ro u g h c a lc u la tio n s , i t a p p e a rs t h a t b a r o m e tr ic d is tu rb a n c e s a c c o m p a n y in g reg io n a l an d local s to rm s of n o rm a l in te n s ity m a y tr a v e l a s f a r a s 150 m iles fro m th e m o u n ta in s , a t v e lo c itie s as h ig h a s 80 m iles an h o u r. A tte n u a tio n of th e s e d is tu rb a n c e s is r a p id , a n d th e y m a y be c o m p le te ly m a sk e d , a t a p o in t so m e d is ta n c e fro m th e m o u n ta in s, b y p u r e ly lo cal b a r o m e tr ic d is tu rb a n c e s . In th e m o u n ta in s , a n a n e ro id te n d s to re a d r a th e r c o n ­ s is te n tly fro m s u n s e t u n til 10 a . m . T h e d r ift, a t 9,000 feet, on an in s tr u m e n t c a lib r a te d in fee t, is a b o u t 30 fe e t p e r h o u r ; d o w n w ard ( in d ic a tin g lo w er e le v a tio n ) u n til a b o u t tw o A . M . , th e n u p w a rd (h ig h e r e le v a tio n , lo w er p re ssu re ) fo r a n h o u r o r so, th e n d o w n w a rd a g a in u n til m id m o rn in g . F ro m m id ­ m o rn in g u n til j u s t b e fo re s u n s e t, th e n ee d le “ j i t t e r s ” v io ­ len tly , a n d a ltitu d e m e a s u r e m e n ts m a d e w ith a n a n e ro id d u rin g th is tim e a re c o r r e c t w ith in 500 fe e t o n ly b y ch a n ce . D u rin g m id a fte rn o o n , fro m th e tim e of fo rm a tio n of th e

736

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d e n s e s t c u m u li o f th e r e g io n a l a n d v a lle y s to r m s u n t i l t h e s k y c le a rs s h o r tly b e fo re s u n s e t, a l t i t u d e r e a d in g s a t 1 4 ,0 0 0 f e e t m a y b e a s m u c h a s 3 ,0 0 0 f e e t off, p lu s o r m in u s , a n d tw o r e a d in g s in th e s a m e lo c a tio n , t a k e n a t in t e r v a l s o f o n e m in u te , m a y d iffe r b y 1,000 f e e t. F i g . 16.

V alley

Storm

C louds

S t r e a m in g

t h r o u g h

G aps

in

t h e

C o n t in e n t a l

D iv id e .

T h is n o rm a l m id a f te r n o o n p h e n o m e n o n w a s p h o t o g ra p h e d fro m t h e s u m m it o f N a v a jo P e a k (F ig . 15), t h e v ie w in c lu d in g t h e c irq u e a t t h e h e a d o f t h e A lb io n V a lle y (F ig . n ) a n d W h e e le r B a sin (th r o u g h t h e g a p ). T h e s e c lo u d s o rig in a te d in W h e e le r B a s in a n d t h e C r a te r L a k e H ellh o le, a n d a f t e r “ w o rm in g t h e ir w a y ” t h r o u g h g a p s in t h e d iv id e , t h e y re f o r m e d , a t a b o u t 12.000 fee t, in to c u m u li w h ic h w e re s o o n to s s e d u p w a r d b y a ir c u r r e n ts of p la in s o rig in , a n d l a t e r p r e c ip ita te d r a in a n d h a il o n to t h e e a s t f la n k of t h e F r o n t R a n g e n e a r t h e d iv id e .

A v e r y h e a v ily d a m p e d i n s t r u m e n t , s u c h a s a m e r c u r ia l b a r o m e te r , in d ic a te s a p r o n o u n c e d a f te r n o o n “ l o w ” o v e r th e m o u n ta in s w h ile re g io n a l a n d lo c a l s to r m s a r e f o rm in g . In t h is c o n n e c tio n i t is i n te r e s ti n g t o n o te t h a t m a n y o f t h e m a jo r C o lo ra d o p e a k s , n o w k n o w n t o b e less t h a n 1 4 ,5 0 0 f e e t h ig h , w e re a s s ig n e d a l titu d e s o f m o r e t h a n 1 7 ,0 0 0 f e e t b y th e p io n e e r s u r v e y o r s , w h o d e t e r m in e d e le v a tio n s f ro m t h e t e m ­ p e r a tu r e o f b o ilin g w a te r . T h e v e r y f a c t t h a t th e s e a l titu d e s

Dec., 1938.]

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are 3,000 fe e t to o h ig h p ro v e s t h a t th e d e te r m in a tio n s w ere h o n e stly a n d a c c u r a te ly m a d e . P rec ip ita tio n a n d M o istu re T r a n s fe r .— P re c ip ita tio n fro m th e v a lle y a n d re g io n a l s to r m s c a n n o t, in g e n e ra l, b e d iffe r­ e n tia te d . T o ta l p r e c ip ita tio n v a r ie s fro m s o m e th in g m o re th a n o ne in c h p e r s to r m y d a y in c e r ta in sm a ll a re a s w ith in cirques to a b o u t o n e - te n th of a n in c h p e r s to r m y d a y in th e ce n te rs of th e p a rk s . T h is , i t sh o u ld b e re m e m b e re d , is th e rain t h a t re a c h e s th e g ro u n d , n o t th e to ta l p r e c ip ita tio n fro m th e clouds. A s m o s t of th e ra in o v e r th e p a r k s a n d v a lle y s is p a r t of a “ closed c irc u it s y s t e m ” i t is of little re a l im p o rta n c e o u ts id e of th e p a r tic u la r v a lle y o r p a r k , c o n tr ib u tin g little o r n o th in g to th e ru n o ff fro m th e a re a , a n d b e in g re e v a p o r a te d , in general, w ith in less th a n 24 h o u rs. T h e sm a ll f ra c tio n of th e to ta l p r e c ip ita tio n t h a t “ spills o v e r ” th e to p o g ra p h ic b o u n d a r ie s of th e p lace of its m o is tu re origin, h o w ev e r, is of g r e a t c lim a tic im p o rta n c e . T h e “ sp ill­ o v e r ” a m o u n ts to a b o u t 1 /1 0 of a n in c h of w a te r p e r s to rm y d a y on a n a r e a a b o u t a m ile w id e j u s t e a s t of th e c re s t of e a ch m a jo r m o u n ta in ra n g e . A s th e re a re a b o u t 100 d a y s d u rin g an av e rag e y e a r w h e n e ith e r v a lle y o r re g io n a l s to rm s, o r b o th , ta k e place, th is re s u lts in a w e s t-e a s t tr a n s f e r of a b o u t 550 a c re -fe e t of w a te r fo r e a c h lin e a r m ile of ran g e , o r a n e v e n tu a l tra n sfe r of a b o u t 130,000 a c re -fe e t of w a te r fro m th e C o lo ra d o to th e M ississip p i d ra in a g e , little of w h ic h is re c o rd e d b y th e rain g au g e s of th e w e a th e r s ta tio n s ! T h is is a b o u t 1/25 of a cubic m ile of w a te r . A v e r y sm a ll a m o u n t of m o is tu re is also tra n s fe rre d fro m th e C o lo ra d o to th e R io G ra n d e d ra in a g e . T hese figures, w h ic h d o n o t in c lu d e th e v e r y v io le n t rain s an d o cc asio n al sn o w s b r o u g h t to th e h ig h c o u n try b y cyclones, are b ased on a d m itte d ly c ru d e m e a s u re m e n ts , a n d a re p r o b ­ ab ly m in im a , r a th e r th a n a v e ra g e s . E x p la n a to ry H y p o th e s is .— V a lle y sto rm s , lik e th e reg io n a l storm s, seem q u ite d e fin ite ly to b e “ closed c i r c u i t ” conv ec tio n a l p h e n o m e n a . T h e y d iffe r fro m th e re g io n a l s to rm s in t h a t th e c irc u it is s h o r te r , a n d less a ffe c te d b y o u ts id e influences, su c h as cy c lo n e s, a n tic y c lo n e s, a n d re g io n a l d ro u g h ts.

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F r o m field o b s e r v a tio n s , i t s e e m s t h a t th e s e s to r m s v a r y in v io le n c e w ith v a r i a t i o n s in a v a ila b le e n e r g y (e ffe c tiv e in s o ­ la tio n ) , a v a ila b le w a te r , a i r c ir c u la tio n , a n d t h e to p o g r a p h ic f a c to r s a l r e a d y d e s c r ib e d . D u r i n g t h e f ir s t p a r t o f th e s u m m e r , d a ily lo ss f ro m “ e s c a p e d ” m o is tu r e s e e m s t o b e m o re t h a n re p la c e d b y w a t e r fre e d b y th e m e ltin g o f s n o w ­ field s a t t h e v a lle y h e a d s . T h e e x c e s s w a t e r r u n s off, a n d in c re a s e s t h a t a v a ila b le in th e p a r k in to w h ic h th e v a lle y d r a in s . A s th e w a te r le v e l in t h e w e t m e a d o w s , o c c u p y in g m u c h o f th e m e ltin g b a s in r e m a in s r e la tiv e ly c o n s t a n t fo r m u c h o f th e v a lle y s to r m se a s o n , th e w a t e r a v a ila b le fo r e v a p o r a tio n in th e v a lle y is q u ite c o n s ta n t . T h e in te n s it y F i g . 17.

xn

xn

B a ro g ra p h T ra c e s, D e n v e r a n d B o u ld e r, J u ly 1 8 -2 1 , 1933. ( D a t a fro m U . S. W e a th e r B u r e a u a n d t h e U n iv e rs ity o f C o lo ra d o .)

C o m p a ra tiv e

T h e s e t ra c e s a r e of a n o rm a l in te r v a l, w h e n “ o u t s i d e ” in flu e n c e s w e re sm a ll, a n d t h e m o u n ta in s to r m s , b o th re g io n a l a n d v a lle y , w e re b e h a v in g in t h e “ t r a d i t i o n a l ” m a n n e r . N o te t h e “ ste p s le a d in g d o w n ” in t h e B o u ld e r t r a c e e a c h a fte rn o o n , c a u s e d b y t h e s e q u e n t b r e a k in g o f t h e v a lle y s to rm s o n t h e e a s te r n e d g e o f M id d le P a r k (F ig . 1), a n d t h e s im ila r s te p s in t h e D e n v e r tra c e , w h ich a re n o t so s h a r p ly d e fin e d , a s D e n v e r is f a r t h e r fro m t h e m o u n ta in s . T h e t r a c e o f t h e 2 0 th is c h a ra c te r is tic of th o se p ro d u c e d b y a n e x tr a -v io le n t re g io n a l s to r m o v e r S o u th P a r k .

o f a g iv e n v a lle y s to r m , th e n , s e e m s d e p e n d e n t o n th r e e v a r ia b le f a c to r s — e ffe c tiv e in s o la tio n , a i r c ir c u la tio n , a n d th e a tm o s p h e r ic th e r m a l g r a d ie n t. A s th e s e th r e e n o r m a lly v a r y o n ly w ith in q u ite n a r r o w lim its , th e u s u a l r e g u la r p e r io d ic ity o f t h e v a lle y s to r m s is n o t s u r p r is in g . T h e d a ily c y c le in a v a lle y s to r m a r e a b e g in s w ith ra p id h e a tin g a n d h u m id ific a tio n o f t h e a i r o v e r t h e m o is tu re so u rc e , u s u a lly th e w e t m e a d o w s in a g la c ia l m e ltin g b a s in . I t s e e m s p r o b a b le t h a t f ro m th e s e w e t m e a d o w s th e r e is m o re e v a p o r a tio n p e r a c re , e a r ly in th e m o r n in g , t h a n is p o ssib le fro m a s im ila r a r e a of la k e s u rfa c e , fo r t h e t o t a l a r e a fro m w h ic h e v a p o r a tio n c a n o c c u r in a v e g e ta tio n - c o v e r e d m e a d o w

Dec., 1938.]

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is fa r g r e a te r th a n th e a c re a g e , a n d e a c h b la d e of g rass, e a rly in th e m o rn in g , is c o v e re d w ith d ew . A s a r e s u lt of th is h ea tin g a n d e v a p o r a tio n , a la rg e v o lu m e of b u o y a n t, w arm , m oist a ir is p r e s e n t in th e lo w e r p a r t of a v a lle y , a n d , e x p a n d ­ ing, seeks th e e a s ie s t o u tle t. M a jo r relief is lim ite d b y to p o g ra p h y to th r e e d ire c tio n s — v e r tic a lly u p w a rd , u p v a lle y , and d o w n v a lle y . M in o r relief is possib le a lo n g th e v a lle y w alls, b u t n o im p o r ta n t a ir c u r r e n ts h a v e b e e n o b se rv e d along v a lle y w alls b elo w th e c irq u e s, p r o b a b ly b ec au se of th e ir steepness. D o w n v a lle y relief of p re s s u re se ld o m ta k e s p la ce , fo r b o th th e b u o y a n c y o f th e a ir, a n d th e m a sse s of co o ler, d e n s e r a ir d o w n v alley o p p o se su c h m o tio n . O fte n , th e o n ly o u tle t fro m a m e ltin g b a sin is a n a r r o w c a n y o n , su fficie n tly la rg e to c a rry several tim e s th e p r e s e n t ru n o ff fro m th e v a lle y , b u t to o sm all to p e rm it ra p id m o tio n of la rg e q u a n titie s of a ir in e ith e r d irection. V e rtic a lly a b o v e th e m e ltin g b asin s, relief u n d o u b te d ly takes place, a n d so m e of th e h e a te d m o is t a ir is d ilu te d an d carried u p w a rd b y th e re g io n a l s to r m c o n v e c tio n s. T h e c u rre n ts risin g a lo n g th e w a lls of th e la rg e r to p o g ra p h ic basins, in to w h ic h m a n y of th e g la c ia te d v a lle y s d ra in , te n d to give a n u p v a lle y m o tio n to a n y a ir c o m in g in to c o n ta c t w ith th e m fro m b elo w . C u r r e n ts fro m th e p la in s h a v e an alm ost id e n tic a l effect. T h e p re v a ilin g w in d s, a c tin g fro m th e w est, g iv e a slig h t u p valley m o tio n to a ir in th e w in d w a rd -fa c in g v a lle y s , an d also s tre n g th e n th e p a rk -w a ll c o n v e c tio n s o v e r th e m . In th e low er p a r ts of le e w a rd -fa c in g v a lle y s , th e effe c t of th e p re ­ vailing w in d s seem s to b e m in o r a n d in h ib ito ry . As a re s u lt of th e a c tio n s of th e se v a rio u s forces, th e re is, in th e region of th e m e ltin g b a sin s, in m id m o rn in g , a n u n ­ stable m a ss of w a rm m o is t air, w ith a s tro n g te n d e n c y to m ove u p v alley , a t a g r a d ie n t s o m e w h a t s te e p e r th a n t h a t of th e v alley floor. W hile th e m e ltin g -b a s in a ir is b e in g h e a te d a n d h u m id ified , the a ir of th e h ig h c irq u e s is b e in g h e a te d , g iv in g i t a te n d e n c y to rise. C o n v e c tio n s of sm a ll m a g n itu d e a re s e t u p in th e cirques, le ad in g to th e f o rm a tio n of th e e p h e m e ra l m o rn in g

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c lo u d w is p s a b o v e th e m . B y m id m o rn in g , th e c ir q u e a i r is u n s ta b le , a n d te n d s to ris e v e r ti c a l ly . A ir in th e t r i b u t a r y v a lle y s b e g in s t o h e a t a s so o n a s s u n ­ lig h t re a c h e s th e v a lle y floors, a n d lik e w ise b e c o m e s b u o y a n t a n d u n s ta b le . G iv e n a s lig h t u p v a lle y m o tio n b y t h e p r e v a il­ in g w in d s a n d t h e p a r k - w a ll c o n v e c tio n s , a n d p u s h e d b y th e m e ltin g - b a s in a i r b e lo w it, t h e a ir t h a t s p e n t th e n i g h t in th e t r i b u t a r y v a lle y s m o v e s u p w a r d in to t h e c irq u e s , fo rc in g th e c irq u e a ir u p w a r d , a n d is r e p la c e d b y w a r m e r , w e t t e r m e ltin g b a s in a ir. T h is s h if tin g of a ir ta k e s so m e tim e , b u t i t is th e b e g in n in g o f th e a f te r n o o n " c h i m n e y ” c ir c u la tio n . F o r m a t i o n o f th e la s tin g c u m u li o v e r th e c irq u e s lo g ic a lly t a k e s p la c e a s so o n a s so m e o f th e v e r y m o is t m e ltin g - b a s in a i r ris e s in to t h e a ir s t r a t a o v e r th e c irq u e s , a n d c o n tin u e s u n t i l p r e c ip ita tio n ta k e s p la c e , o r t h e " c h i m n e y ” c u r r e n t s c e a se , b e c a u s e o f d e c re a s in g in s o la tio n , v e r y la te in t h e d a y . R a in fa llin g in to th e v a lle y s y s te m f ro m w h ic h i t o r ig in a te d r e t u r n s to th e w e t m e a d o w s d u r in g t h e n ig h t, a n d so m e o f it is a g a in e v a p o r a te d th e n e x t d a y . T h e e n t ir e w a t e r c irc u it, e x c e p t f o r t h e sm a ll a m o u n t of m o is tu r e t h a t “ e s c a p e s ” o v e r d iv id e s , is q u ite d e fin ite a n d e a s ily o b s e rv a b le . T h e r e tu r n p a t h o f t h e a i r w h ic h rise s in th e " c h i m n e y c u r r e n t s , ” h o w ­ e v e r, is n o t s u r e ly k n o w n . A s m a ll a m o u n t o f co o l d r y a ir d r if t s d o w n th e in te r v a lle y d iv id e s , w h ic h u s u a lly h a v e a r a t h e r fla t u p p e r s u rfa c e , b u t t h is r e tu r n , b y t h e m o s t g e n e ro u s e s tim a te s , a c c o u n ts fo r o n ly a b o u t o n e p e r c e n t, o f t h e a ir t h a t is c a r rie d u p w a r d b y th e v a lle y s to r m s . O th e r P h e n o m e n a .

N u m e r o u s p ic tu r e s q u e , in te r e s tin g , o r te r r if y in g m in o r p h e n o m e n a a r e r e p o r te d b y m o u n ta in e e r s a n d v is i to r s to th e m o u n ta in s , a n d so m e o f th e s e h a v e b e e n o b s e rv e d o f te n e n o u g h t o p e r m i t f a ir ly a c c u r a te d e s c r ip tio n s a n d p a r t i a l a n a ly s is of th e fo rc e s in v o lv e d . C loud P lu m e s .— A m o n g t h e p ic tu r e s q u e s ig h ts o n m a n y s u m m e r d a y s a re th e g r e a t c lo u d p lu m e s t h a t s t r e a m e a s t ­ w a rd , s o m e tim e s fo r m iles, f ro m th e h ig h p e a k s . T h e s e a r e b e s t d e v e lo p e d a b o u t th o s e m a jo r p e a k s t h a t a r e s e v e r a l m iles e a s t o f th e r a n g e c re s t, s u c h a s L o n g s P e a k a n d M t . E v a n s

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F i g . 18.

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Large volum es of v e ry w a rm , n e a rly s a tu r a te d a ir, risin g fro m th re e g re a t c irq u e s c u t in to th e flanks of L ongs P e a k , a n d co m in g su d d e n ly in to c o n ta c t w ith th e v e ry cold rap id ly -m o v in g su m m it winds a t a b o u t 14,000 fe e t, c au se th is p lu m e , w h ic h e x te n d s m o re t h a n te n m iles e a st of its source. Plum es of th is g re a t e x te n t a re n o t co m m o n .

742

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[J. F . I.

T h e g r e a te s t of th e s e p lu m e s se e m t o b e v a l le y s to r m s w h o se n o r m a l c o u rs e w a s u p s e t b y t h e e ffe c ts of v io le n t cold s u m m it w in d s e a s t o f th e m a in F r o n t R a n g e (F ig . 18). W h e n th e s u m m it w in d s n e a r L o n g s P e a k a r e e s p e c ia lly co ld , t h e v a lle y s b e lo w t h e p e a k s a b n o r m a lly w a r m , a n d t h e w a te r s u p p ly in th o s e v a lle y s a d e q u a t e , g i a n t p lu m e s o f t h is ty p e m a y b e e x p e c te d . T h e s e c o n d itio n s o c c u r o n ly a few tim e s a y e a r. W a r m e d a n d n e a r ly s a t u r a t e d a ir, fro m th e m e ltin g b a s in s of e x t in c t g la c ie rs in th e le e w a r d - fa c in g v a lle y s , ris e s u p w a r d in a n u m b e r of c irq u e s c u t in to th e s h e lte r in g fla n k s o f th e s e g r e a t p e a k s , a n d s u d d e n ly c o m e s in to c o n t a c t w ith th e b itte r co ld , r a p id ly -m o v in g s u m m it w in d s . I m m e d ia te c lo u d f o rm a ­ tio n ta k e s p la c e , a n d t h e r e s u l t a n t c u m u li a r e c a r r ie d so m e m ile s b y th e w in d b e fo re th e y fin a lly d is s ip a te . W e r e i t n o t fo r t h e v io le n c e o f th e s u m m it w in d s o n th o s e r a r e o c c a s io n s w h e n a i r fro m th e le e w a rd v a lle y s c a r rie s its m o is tu r e a s h ig h a s 14,000 fe e t, p r e c ip ita tio n w o u ld t a k e p la c e w ith in a few h u n d r e d f e e t o f th e z o n e o f c o n t a c t b e tw e e n th e v a lle y a ir a n d th e s u m m it w in d s , a n d th e m o is tu r e w o u ld flow b a c k to th e m e ltin g b a s in s . T h is w o u ld b e a n o r m a l v a lle y s to r m . C lo u d p lu m e s fo rm e d w h e re m o is t a ir f ro m o n e c irq u e c o m e s in to c o n t a c t w ith n o rm a lly -c o o l s u m m it w in d s a re q u ite c o m m o n , re s e m b le th e b a n n e r c lo u d d e s c r ib e d b y H u m p h r e y s ,13 a n d h a v e a le n g th s e ld o m e x c e e d in g o n e m ile. T h e s e a p p e a r to b e n o r m a l r e c u r r e n t p h e n o m e n a w h e n n o t s u p p r e s s e d b y th e v a lle y s to r m s , a n d a r e f r e q u e n tl y n o te d , a t a ll se a so n s, to le e w a rd o f m a n y o f t h e h ig h e r p e a k s . T h e s e p lu m e s a r e u se d a s w e a th e r in d ic a to r s b y r e s id e n ts o f th e m o u n ta in re g io n : a r a t h e r fla t-ly in g p lu m e in d ic a tin g h ig h w in d s in th e m o u n ta in s , a d e n s e p lu m e w a r n in g o f v e r y c o ld w e a th e r “ o n t o p , ” a n e a r ly v e r ti c a l p lu m e te llin g of m ild w in d s in t h e h ig h c o u n t r y , a n d n o p lu m e s u g g e s tin g w a r m a ir o n th e s u m m its . T h is u se s e e m s to b e ju s tifie d , t h e p r e d ic te d h ig h c o u n t r y w e a th e r a g r e e in g q u i t e c lo sely w ith w h a t is l a te r e n c o u n te r e d . A s c h e m a tic d ia g r a m , s h o w ­ in g f a c to r s in th e f o r m a tio n o f a n o r m a l p lu m e , s e c u r in g its m o is tu r e f ro m a sin g le c irq u e , a n d n o t c o m p lic a te d b y th e p re s e n c e o f v a lle y s to r m c lo u d s, is sh o w n in F ig . 19.

D ec., 1938.]

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E lectrical E ffe c ts .— N u m e r o u s e le c tric a l effects h a v e b een rep o rted fro m v a rio u s lo c a tio n s in th e h ig h c o u n try , a n d som e of th e se h a v e b e e n r e p e a te d ly o b se rv e d . D ire c t s tro k e s of lig h tn in g a re c o m m o n a t h ig h a ltitu d e s , p a rtic u la rly in c e r ta in r a th e r lim ite d a re a s, w h ich a re lo cally F i g . 19.

COLD

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F o r m a t io n .

Leew ard of a high p e a k , w h e re g la c ia tio n h a s o v e rs te e p e n e d th e slopes, w arm m oist a ir from the valley rises in th e s h e lte re d c irq u e , fo rm in g e p h e m e ra l clo u d w isps as th e a ir cools, a n d dense plumes of cloud w h en t h e u p d r a f ts m e e t th e cold a n d ra p id ly -m o v in g su m m it w inds. A t som e distance from th e p e a k , th e p lu m e w id en s a n d fin ally d issip a te s as it m ixes w ith th e cold d ry air of the sum m it w inds. C o n d itio n s h e re sh o w n a re th o se in th e C h asm of L ongs P e a k , n e a r E stes Park, C olorado.

rep u te d to “ d r a w ” lig h tn in g . Q u a n d a ry P e a k , in th e M o sq u ito R a n g e (F ig . 1, n u m b e r 11), is o n e of th e se. I n v e s ti­ gation show s t h a t d ir e c t s tr o k e s of lig h tn in g to th is s u m m it are e x tre m e ly n u m e ro u s , a n d t h a t th e p ro b a b le c a u se is a dike of b la c k , s o m e w h a t m a g n e tic m a te r ia l t h a t ru n s v e rtic a lly th ro u g h th e p e a k , a n d fo rm s th e s u m m it rid g e. In som e of

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th e o th e r r e p e a te d ly - s tr u c k a r e a s , th e p r o b a b le c a u s e is n o t so e a s ily d e te r m in e d . C a ir n s o n th e h ig h e r p e a k s a r e f r e q u e n tl y d e m o lis h e d b y lig h tn in g , a n d tr e e s n e a r tim b e r lin e a r e s o m e tim e s b la s t e d in to s m a ll c h ip s b y d ir e c t s tr o k e s . L ig h tn in g c a u s e s a b o u t tw o d e a th s a n n u a lly in th e m o u n ta in s , h u m a n s b e in g u n a b le to s u r v iv e a d ir e c t s tr o k e . I n d u c e d c h a rg e s , a s e c o n d a r y e ffe c t o f lig h tn in g , m a k e life m is e r a b le fo r c o m m u n ic a tio n a n d p o w e r c o m p a n ie s s e rv in g th e m o u n ta in re g io n . C lim b e rs f r e q u e n tl y a r e k n o c k e d d o w n b y in d u c e d c h a rg e s , w h ic h d o n o s e v e re p h y s ic a l d a m a g e , b u t c a u s e r a t h e r s e v e re n e r v o u s s h o c k w h ic h m a y la s t so m e h o u r s . M ild e r in d u c tio n s s o m e tim e s p r o d u c e p s e u d o r h e u ­ m a tic p a in s , w h ic h p a s s in a few m in u te s . H a t s a r e s o m e tim e s lif te d off b y in d u c tio n d is c h a rg e s , a n d w o m e n a r e g r e a tly a n n o y e d b y t h e ir h a ir, w h ic h lit e r a ll y s t a n d s o n e n d u n til t h e e le c tric a l d is tu r b a n c e s a r e o v e r. A f a v o r ite s t u n t of m o u n ta in g u id e s , w h e n th e a ir is th o r o u g h ly c h a rg e d , is to i m i t a t e T h o r b y w a v in g a n ice-ax e o v e r th e i r h e a d s . T h e m e ta l p a r t s o f th e ic e -a x e d r a w d o w n a n im p r e s s iv e d is p la y of e le c tric a l p y r o te c h n ic s . A g e o ­ lo g ic a l h a m m e r w ill s o m e tim e s s p i t lo n g h o t s p a r k s in one p o s itio n , b u t if th e h e a d is t u r n e d a t r i g h t a n g le s t o th e f o rm e r p o s itio n , th e s p a r k in g s to p s . M o u n ta in e e r s a r e fre ­ q u e n t ly a la r m e d b y th e s p a r k s e m itte d b y t h e i r m e ta l h o b ­ n a ils , w ith t h e r e s u ltin g m ild s h o c k s . T h e y u s u a lly d e t e c t c h a r g e d a i r b y ra is in g a fin g e r a b o v e t h e i r h e a d s . W h e n th e a ir is h e a v ily c h a rg e d , s p a r k s w ill siz zle f ro m t h e fin g e rtip , m a k in g a n o ise lik e f ry in g b a c o n . I n d u c e d e le c tric a l d is c h a r g e s f r e q u e n tl y d e m a g n e tiz e o r r e v e rs e c o m p a sse s, a n d r u in p h o to g r a p h i c film s b y d is c h a r g in g in s id e c a m e r a s o r film h o ld e rs . O c c a s io n a lly w a tc h e s a n d a n e r o id b a r o m e te r s n e e d r e a d ju s tin g a f t e r b e in g c a r rie d th r o u g h v io le n t h ig h - a ltitu d e e le c tric a l s to r m s . B a ll lig h tn in g is o c c a s io n a lly r e p o r te d b y c lim b e rs , a n d m a n y o f th e r e p o r ts a r e u n d o u b te d ly g e n u in e — t h a t is, th e c lim b e r h o n e s tly b e lie v e s h e s a w j u s t w h a t h e r e p o r ts . I t is in te r e s ti n g to n o te , in t h is c o n n e c tio n , t h a t a lu m in o u s v is u a l im a g e , t h a t s e e m in g ly t r a v e l s q u i t e a d is ta n c e , fin a lly c h a n g in g c o lo r a n d d y in g o u t, c a n b e p r o d u c e d b y firin g a p h o to f la s h

Dec., 1938.]

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b u lb w ith o u t w a rn in g so m e w h e re n e a r th e o u te r lim it of a “ v ic tim ’s ” field of v isio n . H e w ill r e p o r t t h a t a g re e n ish o r reddish b a ll w a n d e re d in to h is v is u a l field (“ tra v e le d alo n g th e w all in f r o n t of m e ” ), b e c a m e sm a lle r a n d c h a n g e d co lo r n ea r its c e n te r (“ r ig h t in f r o n t of m e ” ), th e n v a n is h e d su d d en ly . T h e s u b je c t sh o u ld n o t k n o w in a d v a n c e w h a t is going to h a p p e n , a n d n o tw o p eo p le w ill giv e id e n tic a l re p o r ts of th e ir se n s a tio n s w h e n th is e x p e rim e n t is tr ie d . F ro m th is , and th e la c k of a m o re s a tis f a c to r y e x p la n a tio n , it is su g g e sted th a t b all lig h tn in g is a n o p tic a l illu sio n , ca u se d b y a v e ry b rillia n t lig h tn in g d is c h a rg e so m e w h ere n e a r th e lim its of th e o b serv er’s v is u a l field. C oronas, h alo s, a n d s ta n d in g arc s h a v e se v e ra l tim e s b een observed b y th e w r ite r w h e n s p e n d in g th e n ig h t a t v e ry h ig h altitu d e s (ab o v e 12,000 fe e t). T h e se p h e n o m e n a , n e v e r tw ice the sam e, so m e tim e s a t t a i n c o n s id e ra b le b rillian ce , a n d se e m ­ ingly h a v e th e ir so u rc e in so m e in s u la te d c o n d u c tin g m e ta l object. C oronas, as th e te r m is h e re used, a re lu m in o u s d isc h a rg e s origin atin g on th e su rfa c e of a n o b je c t a n d e x te n d in g o u tw a rd for som e d is ta n c e (so m e tim e s se v e ra l fe e t). T h e y a re u su a lly red or re d d ish -p u rp le , a lth o u g h a b r illia n t g ree n c o ro n a h a s been seen tw ic e ; a n d ro u g h ly re se m b le in o u tlin e th e o b je c t from w hich th e y e x te n d . O fte n , w h en c o ro n a s a re p re se n t, a person w ill a p p a r e n tly b e b a th e d in flam es, a lth o u g h he h im ­ self w ill be u n a w a re of it. A t tim e s, th e so u rce of a c o ro n a will give v e r y se v ere e le c tric sh o c k s w h e n to u c h e d , a t o th e r tim es it seem s e le c tric a lly “ d e a d ” a n d m a y be c o n ta c te d w ith im p u n ity . H alos are p r o b a b ly sp e c ia l cases of co ro n a s, h a v in g th e sam e colors a n d fo rm , b u t b e tw e e n th e h alo a n d th e h alo ed o b ject th e re is a w ell-d efin ed n o n lu m in o u s zone. B o th h alo s and co ro n a s te n d to b e m o re b r illia n t in o n e v e r tic a l p la n e th a n a n o th e r, so t h a t a h a lo a ro u n d a p erso n m a y b e m o re easily v isib le in pro file th a n in “ full fa c e .” T h is p la n e of m axim um b rillia n c e v a rie s in d ire c tio n fro m p lace to p lace, and m a y n o t h a v e th e s a m e b e a rin g fo r tw o su ccessiv e m inutes. On sev eral o cc asio n s, s ta n d in g arcs, w h ich co u ld b e d ra w n o u t from a c o n d u c tin g o b je c t, su c h as th e h e a d of a n ice-axe,

7 46

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o r so m e o n e 's n o se , a n d th e n w o u ld c o n tin u e to fla re f o r so m e tim e , w e re n o te d . T h e s e e x a c tly r e s e m b le d t h e s ta n d i n g a rc s p r o d u c e d f ro m h ig h - f r e q u e n c y e q u ip m e n t, a n d c a u s e d m in o r b u r n s id e n tic a l in a p p e a r a n c e a n d slo w n e ss o f h e a lin g w ith th e “ h ig h fre q u e n c y b u r n s " su ffe re d b y r a d io e x p e r im e n te r s . E x a c tly h o w a h ig h - fr e q u e n c y d is c h a r g e c a n o c c u r in n a t u r e is n o t c le a r t o th e w r ite r , a n d n o e x p la n a tio n is o ffe re d fo r th e s e s ta n d in g a rc s. A tt e m p t s to m e a s u r e th e d ir e c tio n a l p r o p e r tie s of h ig h a l titu d e e le c tric a l p h e n o m e n a , u s in g tw o te n fo o t le n g th s of w ire a n d a sm a ll n e o n b u lb , w e re n o t w h o lly su c c e ssfu l. W h ile e v e r y m in o r effe c t h a d a d e f in ite m a x im u m s tr e n g t h in so m e a z im u th , th e r e se e m e d t o b e n o d e f in ite r e la tio n b e tw e e n th is a n d e ith e r th e e a r t h ’s m a g n e tic field o r th e to p o g r a p h y . W i th s tr o n g e r m a n if e s ta tio n s , th e r e s u lts w ere e v e n less in f o rm a tiv e , th e n e o n b u lb u s u a lly fla rin g w ith e x tr e m e b rillia n c e fo r a m o m e n t a n d th e n e x p lo d in g . B e c a u se o f th e g r e a t d iffic u lty of g e t tin g n e o n b u lb s in t h e m o u n ta in s , a n d th e v e r y s e v e re sh o c k s su ffe re d w h e n h a n d lin g w ire on h ig h p e a k s d u r in g s ta tic s to r m s , th e s e e x p e r im e n ts w ere c a r rie d n o f u r th e r . S o m e w h a t s im ila r e le c tric a l p h e n o m e n a h a v e b e e n r e ­ p o r te d f ro m th e c o sm ic r a y la b o r a to r y 14 o n M t. E v a n s ( 1 4 ,0 0 0 + fe e t, in th e F r o n t R a n g e , n e a r D e n v e r ) , w h ich s e e m s to b e a b n o r m a lly p r o n e t o s t a t i c s to r m s a n d lig h tn in g d is c h a r g e s of u n u s u a l v io le n c e . B a c k d r a fts .— M a n y le e w a rd -fa c in g v a lle y s n e a r th e m o u n ­ ta in s u m m its a re n o te d fo r t h e i r v io le n t r e v e rs in g w in d s, lo c a lly c a lle d b a c k d r a f ts , w h ic h se e m to b e c a u s e d b y th e b lo w in g o f a b n o r m a lly - s tr o n g s u m m it w in d s a c ro s s d e e p , s te e p -w a ile d c irq u e s . A n u m b e r o f th e s e b a c k d r a f ts h a v e b e e n o b s e rv e d fro m th e c irq u e s a t th e h e a d s o f th e v a lle y s in w h ic h t h e y o cc u r, a n d b a r o m e tr ic a n d w in d o b s e r v a tio n s m a d e d u r in g th e w o rs t o f th e a tm o s p h e r ic d is tu r b a n c e s . M o s t o f th e s e w in d s o c c u r in c irq u e s c u t in to t h e e a s te r n fla n k s o f h ig h p e a k s so m e d is ta n c e e a s t o f th e m a in ra n g e s , a n d re c e iv in g , in c o n s e q u e n c e o f th e i r lo c a tio n , m o r e v io le n t w in d t h a n p e a k s clo se r to o r in te g r a l p a r t s o f t h e ra n g e s. C irq u e flo o rs a r e u s u a lly a b o u t 12,000 f e e t a b o v e s e a lev el, t h e c irq u e h e a d w a lls risin g a b o u t 2 ,0 0 0 f e e t h ig h e r.

D ec., 1938.]

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D u rin g a w in d s to rm of th is ty p e , a b a r o m e te r in th e cirq u e w ill slow ly d ro p to a b o u t 14 in ch es, a s th e w in d , F ig . 20.

HIGH

W IND

NO WIND

BACK

DRAFT ■M .O OO'i

C o n d it io n s

P r o d u c in g

B ackdrafts.

F o r som e m in u te s, w inds blow acro ss h ig h cirq u e s, su ck in g o u t th e air, a s p ira to r-fa sh io n , a n d depressing th e b a ro m e te r fa r b elow its n o rm a l rea d in g . T h is c o n d itio n is sh o w n in A , th e arro w s in d icatin g directio n s of m o tio n , n o i th e forces a t w o rk . A fte r a n a p p re c iab le tim e , th e su m m it w ind ceases, a n d th e b a c k d ra ft ru sh e s in to th e c irq u e , overfilling it w ith a ir, a n d raisin g th e b a ro ­ m etric pressure far ab o v e n o rm al fo r th e a ltitu d e . T h is co n d itio n lasts for o n ly p a r t of a m in u te a nd is show n in B . T h e ty p e lo ca tio n fo r th e s e d ra fts is S u m m it L a k e , o n M t. E v a n s, in th e F ro n t R ange, w est of D e n v e r. F ig u re in se rts r e p re s e n t th e e x tre m e b a ro m e tric re a d in g fo r c o n ­ ditions show n in th e m ain figures.

blow ing o v e r th e cirq u e , slo w ly su c k s th e a ir o u t o f it, a s p i­ ra to r-fa sh io n . T h e s u m m it w in d , d u rin g th e b a ro m e tric decline, is e x tre m e ly v io le n t; th e d o w n v a lle y w in d , p ro b a b ly VOL. 226 , NO. I 3 5 6 ----52

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in d u c e d b y th e s u m m it w in d , is m o re m ild , s e ld o m m o v in g f a s te r t h a n a b o u t 30 m .p .h . (F ig . 20, A ) . S u d d e n ly , a f te r so m e m in u te s of d r o p p in g b a r o m e te r , th e s u m m it w in d in th e im m e d ia te v ic in ity o f th e c irq u e s to p s b lo w in g , a n d a t th e s a m e tim e th e b a r o m e tr ic d e c lin e ceases. A fte r a few se c o n d s o f d u ll ro a rin g , th e b a c k d r a f t r u s h e s u p ­ v a lle y in to th e c irq u e , ra is in g th e b a r o m e te r to a n a b n o r m a l h ig h , s o m e tim e s a s g r e a t a s 22 in c h e s (F ig . 20, B ) . T h e n th e s u m m it w in d b e g in s a g a in , a n d th e c y c le r e p e a ts its e lf u n til th e w in d “ b lo w s its e lf o u t . ” A s m ig h t b e e x p e c te d , th e s u d d e n c h a n g e s of b a r o m e tr ic p re s s u re a re e x tre m e ly u n c o m fo rta b le , o fte n p r o d u c in g v e r y v io le n t n a u s e a a n d in te r n a l p a in s, h e a d a c h e s , v e r tig o , a n d co p io u s n o se b le e d s ( “ m o u n ta in s ic k n e s s ” ), e v e n in th o s e th o r o u g h ly a c c u s to m e d to life a b o v e tim b e r lin e . C O N C L U S IO N S .

F ro m th e field o b s e rv a tio n s d e s c rib e d in th is p a p e r , i t is te n ta t iv e l y c o n c lu d e d t h a t : 1. S n o w , b r o u g h t in to th e m o u n ta in re g io n b y t h e w in te r cy c lo n e s, is its o n ly im p o r ta n t so u rc e of m o is tu re . 2. T h e la rg e to p o g r a p h ic b a s in s se rv e a s re s e rv o irs , fro m w h ic h m o is tu re a c c u m u la te d d u r in g th e w in te r g r a d u a lly e sc a p e s d u r in g th e w a r m e r m o n th s a s ru n o ff, a n d b y th e a c tio n o f th e p r e v a ilin g w in d s o n th e c lo u d s o f th e re g io n a l a n d lo cal sto rm s . 3. U n d e r p r e s e n t c o n d itio n s in th e m o u n ta in re g io n , a n in v e rs e r e la tio n of u n k n o w n m a g n itu d e e x is ts b e tw e e n th e m o u n ta in a n d p la in s p r e c ip ita tio n . 4. R e g io n a l a n d v a lle y s to r m s te n d to in c re a s e t h e flow of th e P la tt e a n d A rk a n s a s R iv e rs, a t th e e x p e n s e of th e C o lo ra d o . 5. E le v a tio n of th e lev el of c o n d e n s a tio n o f p a r k - m o is te n e d a ir in to th e “ tr a d e w in d ” s tr a t u m , su c h a s m ig h t b e c a u s e d b y a s lig h t g e n e ra l w a rm in g o r a d e c re a s e in a v a ila b le m o is tu re in th e p a r k s , w o u ld le a d to a su p p re s s io n of th e re g io n a l s to rm s , a ra p id m e ltin g o f w in te r sn o w s, a n d e v e n tu a lly to v io le n t s p rin g floods a n d la te s u m m e r d r o u g h t in th e p a r k s a n d o n th e h ig h p la in s.

D ec., 1938.]

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6. D e p re ss io n of th e level of c o n d e n s a tio n of p a rk m o is te n e d a ir, su c h a s m ig h t be c a u se d b y a n in c re a s e in sn o w fall, o r a s lig h t g e n e ra l cooling, w o u ld te n d to co n fin e p a r k m o is tu re w h o lly w ith in th e p a rk s , re s u ltin g in a n a c c u m u la tio n of sn o w in th e h ig h c irq u e s, le a d in g p e rh a p s to a m in o r ice age, a n d in c re a sin g th e flow of th e C o lo ra d o R iv e r, w h ile d e c re a s in g th e w a te r su p p lie s fro m th e m o u n ­ ta in s to th e P l a t t e a n d A rk a n s a s R iv e rs. A s lig h t in c re a se in th e flow of th e R io G ra n d e m ig h t b e e x p e c te d . T h is w o u ld im m e d ia te ly c a u se d r o u g h t o n th e h ig h p la in s, b u t i t se e m s p r o b a b le t h a t s to r m s sim ila r to th e reg io n a l s to r m s w o u ld so o n b e e s ta b lis h e d a lo n g th e m o u n ta in fro n t, a n d t h a t th e final re s u lt, a f te r so m e o r m a n y y e a rs, w o u ld be a m ild e r, m o is te r, h ig h p la in s su m m e r. A la s tin g g e n e ra l co o lin g w o u ld also ca u se a s o u th w a rd m ig r a tio n of th e c y c lo n e tr a c k s , a u g m e n tin g th e m o is tu re a v a ila b le to th e p la in s d u r in g th e su m m e r, a n d w o u ld in h ib it e v a p o r a tio n a n d th e sp rin g m e lts, p re s e rv in g m o re of th e w in te r sn o w u n til la te in th e se aso n . 7. L o c a l o r v a lle y sto rm s , b e c a u s e of th e p e c u lia r c o n ­ d itio n s c a u s in g th e m , w o u ld b e affe c te d less b y c lim a tic c h a n g e s th a n th e re g io n a l s to rm s. T h e v io le n c e of th e v a lle y s to r m s b e a rs a s o m e w h a t d ir e c t r e la tio n to th e h e a t s u p p ly to th e so u rc e o f m o is tu re , all o th e r th in g s b e in g e q u a l, a n d h en c e, m o re v io le n t v a lle y s to r m s sh o u ld c o n c e iv a b ly r e s u lt fro m a s lig h t w a rm in g , w h ile th e ir in te n s ity sh o u ld d e c re a s e w ith a s lig h t g e n e ra l cooling. G e n e ra l c h a n g e s in te m p e r a t u r e w o u ld v e r y d e fin ite ly c h a n g e th e le n g th of th e v a lle y s to r m se a so n . T h e y w o u ld b eg in e a rlie r in th e y e a r if th e te m p e r a tu r e w ere w a rm e r, a n d w o u ld s to p e a rlie r in v a lle y s h a v in g little sn o w s to ra g e in th e h ig h c irq u e s, b u t w o u ld c o n tin u e u n til la te r in th e y e a r, b e c a u se of p o s tp o n e d fre e z in g of th e w e t m e ad o w s, in th o s e v a lle y s h a v in g a d e q u a te snow s to r a g e in sh e lte re d lo c a tio n s. A d e c re a s e in g e n e ra l te m p e r a tu r e s w o u ld d e la y th e in itia tio n of th e v a lle y s to r m s a n d a c c e le ra te th e ir c e ssa tio n b e c a u s e of e a rlie r fre e z in g of th e m o is tu re so u rces. S o m e v a r ia tio n in th e tr a n s - r a n g e c lo u d d r if t re s u ltin g fro m th e se s to r m s sh o u ld b e e x p e c te d a s a r e s u lt of g e n e ra l te m p e r a tu r e

750

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[J. F. 1.

c h a n g e s , b u t j u s t w h a t t h a t c h a n g e w o u ld b e is h a r d to p r e d ic t u n til m o re q u a n t i t a t i v e d a t a a re a v a ila b le . 8. D a ily a f te rn o o n c lo u d in e s s o v e r th e m o u n ta in re g io n is a n o rm a l c o n d itio n , le a d in g to p o ssib le r a in o v e r th e p a r k s a n d to p r o b a b le r a in o v e r th e h e a d s o f th e m a jo r v a lle y s . A b se n c e of th e re g io n a l c lo u d s tr a t u m , a n d r a in f ro m it, c a n b e e x p e c te d w h e n a n a n tic y c lo n e a r r iv e s o v e r th e m o u n ta in reg io n . In d ra w in g th e s e c o n c lu sio n s, i t is fu lly re a liz e d t h a t b o th th e o b s e rv a tio n a l a n d th e o re tic a l d a t a u se d a r e f a r fro m c o m p le te , a n d t h a t re v isio n s w ill p r o b a b ly b e n e c e s s a r y w h e n m o re a d e q u a te in fo rm a tio n , b o th field a n d la b o r a to r y , is a v a ila b le . A n u m b e r of a d d itio n a l w e a th e r s ta tio n s , lo c a te d in th e v a r io u s p a rk s , a n d a to p th e m o re i m p o r ta n t ra n g e s , w o u ld g r e a tly e x p e d ite th e g a th e r in g of th e v a s t a m o u n t o f o b s e r v a ­ tio n a l d a t a so b a d ly n e e d e d to e x te n d o u r k n o w le d g e of m o u n ta in w e a th e r . U n til th e s e d a t a a r e g a th e r e d , a n d th e ir sig n ific an c e le a rn e d , m o u n ta in re s id e n ts , a n d th o s e d e p e n d e n t u p o n a c c u r a te k n o w le d g e of m o u n ta in w e a th e r c o n d itio n s , p a r tic u la r ly a v a ila b le m o is tu re , fo r th e ir e c o n o m ic o r p h y s ic a l ex iste n c e , w ill su ffe r fro m th e a b s e n c e o f a d e q u a te p r e d ic tio n fa c ilitie s a n d m e th o d s . P O S S IB L E A P P L IC A T IO N S.

F u r t h e r re s e a rc h in to th e p ro b le m o f m o u n ta in w e a th e r , its p re d ic tio n , tr e n d , a n d p o ssib le sig n ific a n c e , m a y le a d to g r e a t in c re a se s in o u r k n o w le d g e in s e v e ra l field s m o re o r less d e p e n d e n t u p o n k n o w le d g e o f w e a th e r c o n d itio n s a n d tr e n d s . T h re e of th e s e fields— geo lo g y , ir rig a tio n , a n d a v ia tio n — w ill b e b rie fly m e n tio n e d h ere . G eology.— M a n y geolo g ic p ro c e sse s a r e so d ir e c tly in ­ flu en c ed b y w e a th e r c o n d itio n s t h a t a v e r y s lig h t c h a n g e in th e w e a th e r, c o n tin u e d o v e r s e v e ra l o r m a n y s e a so n s, w ill c a u se a c o n s id e ra b le c h a n g e in th e p ro c e ss. W e a th e r in g , ero sio n , s e d im e n ta tio n a n d g la c ia tio n a re th e m o s t im p o r t a n t of th e se . In th e m o u n ta in reg io n , fo r e x a m p le , so m e r o c k su rfa c e s a re a l te r n a t e ly w e tte d a n d d r ie d , o th e r s a r e c o n ­ tin u a lly w e t, a n d still o th e r s a re d r y fo r d a y s o r w e e k s a t a tim e . M in o r s h iftin g s o f th e local o r re g io n a l s to r m s , o r

Dec., 1938.]

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R o c k ie s .

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c h a n g e s in th e ir in te n s ity , m a y c h a n g e th e m o d e of ro c k d is in te g r a tio n in a g iv e n a r e a fro m o n e of le a c h in g a n d fro stc ra c k in g to o n e of a rid e x fo lia tio n w ith a lm o s t n o a c c o m ­ p a n y in g c h e m ic a l c h a n g e s . E ro s io n , b e in g a f u n c tio n of th e v e lo c ity of th e e ro d in g w a te rs , r a t h e r th a n of a n n u a l ra in fa ll, w o u ld lik ew ise be g r e a tly in flu e n c e d b y s lig h t c lim a tic c h a n g e s — a n in c re a se in th e v io le n c e o f ra in fa ll, e v e n th o u g h th e to ta l a n n u a l ra in fa ll m ig h t re m a in th e sa m e , m ig h t c a u se a g r e a t in c re a se in to ta l a n n u a l e ro sio n . I t is in te r e s tin g to n o te , in th is c o n n e c tio n , t h a t th e b a s in ra n g e d e s e r ts of n o r th e r n M ex ico , h a v in g th e le a s t ra in fa ll of a n y reg io n in N o r t h A m e ric a , also h a v e th e m o s t r a p id ero sio n , c h ie fly b e c a u s e th e to ta l a n n u a l p r e c ip ita ­ tio n o c c u rs in a v e r y few s to r m s of e x tre m e v io len ce. T h e p r o d u c ts of w e a th e r in g a n d ero sio n a re e v e n tu a lly d e p o s ite d a s se d im e n ts , a n d fro m th e s e i t is so m e tim e s p o ssib le to d e te r m in e th e c o n d itio n s a c c o m p a n y in g e ro sio n o r s e d im e n ta tio n , o r b o th . F ro m th e se , so m e id e a of th e c lim a te d u r in g th e tim e of s e d im e n ta tio n m a y b e g a in e d . W ith th e v a r io u s s to r m ty p e s in th e p r e s e n t R o c k y M o u n ta in reg io n , th e r e m ig h t, c o n c e iv a b ly , b e d e p o s ite d a n u m b e r of d iffe re n t s e d im e n ts, in d a ily ( th r o u g h o u t th e s u m m e r), y e a rly , a n d p e r h a p s o th e r, la y e rs. V a rv e s, r e s u ltin g fro m g la c ia l m e ltin g a n d d e p o s itio n o f o u tw a s h in lak es, h a v e b e e n n o te d in m a n y reg io n s. I n p re v io u s s tu d ie s of s e d im e n ts, r e c u r r e n t la y e rs h a v e a lm o s t in v a r ia b ly b e e n classified a s a n n u a l. F u tu r e w o rk , in th e en c lo se d b a s in s of th e R o c k y M o u n ta in s a t le a st, sh o u ld ta k e in to c o n s id e ra tio n th e p o ssib ility of a m u ltip lic ity of la y e rs d e p o s ite d d u r in g a sin g le y e a r. A n n u a l v a rv e s , w ith d a ily s u b v a rv e s in th e u n o x id iz e d se c tio n , a re a t le a s t th e o ­ r e tic a lly p o ssib le in la k e s re c e iv in g th e ir inflow fro m v a lle y s h a v in g a d a ily s u m m e r s to r m cycle. S tu d ie s of e x is tin g a n d fo rm e r g la c ie rs in th e R o c k y M o u n ta in s m u s t ta k e re c e n t a n d a n c ie n t c lim a te in to c o n ­ s id e ra tio n . T o d a y ’s g la cie rs, se e m in g ly in slow r e tr e a t, a re a n im p o r ta n t f a c to r in th e r e g u la tio n of th e flow of m a n y s tre a m s , a n d in th e m a in te n a n c e of th e re g io n a l a n d local s to rm s . T h e ir p r e s e n t s itu a tio n seem s p re c a rio u s, a s lig h t in c re a se in n e t p r e c ip ita tio n (m o re sn o w o r less m e ltin g )

752

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[J. F . I.

a p p e a r s n e c e s s a ry if th e g la c ie rs a re t o la s t m u c h lo n g e r. A v e r y s lig h t d e c lin e in n e t p r e c ip ita tio n (less sn o w o r m o re m e ltin g ) w o u ld c a u se th e ir r a p id v a n is h m e n t. I t is in te r e s tin g to n o te t h a t in th e v a lle y s h a v in g th e h e a v ie s t ra in fa ll to d a y , th e g la c ie rs a t th e ir m a x im u m e x te n ­ sio n w e re lo n g e st, s u g g e s tin g t h a t th e a r e a l d is t r ib u t io n of p r e c ip ita tio n h a s b e e n a b o u t th e s a m e sin c e a t le a s t m id P le isto c e n e . I r r ig a tio n .— A rtific ia l r e d is tr ib u tio n o f s tr e a m flow , a s a n a id to a g r ic u ltu r e , h a s b e c o m e of m a jo r im p o r ta n c e in th e fla tla n d s a d ja c e n t to th e m o u n ta in s . T h e m a jo r p a r t o f th e w a te r u se d is ru n o ff fro m th e m o u n ta in s , a n d n o t p r e c ip ita ­ tio n o n th e p la in s. W e re i t n o t fo r th is w a te r fro m th e m o u n ta in s , th e p la in s w o u ld b e a d e s e r t, u n f it e v e n fo r g ra z in g . D is re g a rd in g all e c o n o m ic c o n s id e ra tio n s , th e s u p p ly o f ir rig a tio n w a te r is still s tr ic tly lim ite d . N o a m o u n t of p r a y e r, m o n e y , o r le g isla tio n w ill in c re a se th e a v e ra g e a n n u a l p r e c ip ita tio n on th e m o u n ta in re g io n . A ll t h a t c a n b e d o n e is to r e d is tr ib u te th e p r e s e n t ru n o ff fro m n o n a r a b le la n d s to th o s e s u ite d fo r c u ltiv a tio n . R e c e n tly , a n u m b e r of tr a n s m o u n ta i n d iv e rs io n p r o je c ts h a v e b ee n p ro p o se d , th e o b je c t b e in g to r e m o v e w a te r fro m th e C o lo ra d o R iv e r d r a in a g e a n d s u p p ly i t to th e P l a t t e V a lle y . In v ie w of th e a p p a r e n t in v e rs e r e la tio n of m o u n ta in to p la in s ra in fa ll, th e v a lu e of th e s e p r o je c ts a s c o m p e n s a to r y w o rk s, to m a in ta in a c o n s ta n t a v e ra g e w a te r s u p p ly in th e P la tt e V alley , is h a r d ly to be d o u b te d , p r o v id e d th e d iv e rs io n d o e s n o t e v e n tu a lly u p s e t th e s to r m c y c le s in th e b a s in s fro m w h ic h th e w a te r is ta k e n . A s p o te n tia l e v a p o r a tio n f ro m m u c h of th e ir r ig a te d re g io n fa r ex c ee d s th e a m o u n t of w a te r a v a ila b le , it se e m s p ro b a b le t h a t m u c h ir rig a tio n w a te r is w a s te d , b e in g e v a p o r a te d in th e fields a n d c a rrie d g r e a t d is ta n c e s e a s t b y th e w in d s to re g io n s t h a t d o n ’t n e e d it. T h is q u ite d e fin ite ly p ro d u c e s c lim a tic c h a n g e s , o f u n k n o w n , b u t p r o b a b ly v e r y m in o r, m a g n itu d e . In c re a s e d tr a n s m o u n ta in d iv e rsio n , a n d e x p a n s io n o f th e ir rig a te d a re a s, m a y v e r y w ell p ro d u c e s e rio u s d e s ic c a tio n of th e lo w er C o lo ra d o V a lle y , c a u s in g c lim a tic c h a n g e s o f a p p re c ia b le m a g n itu d e in a d j a c e n t a re a s . O w e n s V a lle y , C a lifo rn ia , is a n e x a m p le of a re g io n d e s ic c a te d b y d iv e rs io n

D ec., 1938.]

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R o c k ie s .

753

of its inflow . O n ce th e re w a s s te a m b o a t se rv ic e o n O w en s L a k e . T o d a y th e la k e b a s in c a n b e cro sse d b y a u to m o b ile . U n le ss e x tre m e c a re is ex e rc ise d , o th e r a re a s m a y su ffe r a s im ila r fa te . A v ia tio n .— In th e p a s t, th e R o c k y M o u n ta in s w ere a b a rrie r, to c o v e re d w a g o n tr a v e l, th e n to ra ilro a d c o n s tru c tio n , a n d to d a y th e y a re a d e fin ite m e n a c e to a irc ra ft, p a r tic u la r ly to th o s e c a r ry in g p a s se n g e rs a n d m a il ac ro ss th e m o u n ta in s o n a m o re o r less d e fin ite sc h e d u le . P ilo ts to d a y c a n d e te r m in e th e ir co u rse s a n d lo c a tio n s w ith so m e c e r ta in t y b y th e use of ra d io b e a m s, b u t th e ir a l titu d e is still d e te r m in e d b y a n a n e ro id a ltim e te r, w h ich is r e a s o n a b ly t r u th f u l o n ly in tim e s of c le a r w e a th e r — j u s t w h e n it is le a s t needed! I t is tr u e t h a t b y c lim b in g u n til th e a ltim e te r re a d s 1 7 ,0 0 0 + fe e t all d a n g e r of c ra s h in g in to a m o u n ta in s id e m a y b e a v o id e d , e v e n in th e s to r m ie s t m o u n ta in w e a th e r, b u t th is is h a r d on th e p ilo ts, re d u c e s th e p a y lo a d of th e p la n es, a n d m a y h a v e se rio u s c o n s e q u e n c e s fo r th e p a sse n g e rs, w h o h a v e , in g e n e ra l, little to le ra n c e fo r e ith e r h ig h a ltitu d e o r ra p id a ltitu d e c h a n g e . (T h e se figures a re fo r th e C o lo ra d o -W y o m in g - U ta h -I d a h o reg io n , w h e re n o p e a k s a re o v e r 14,500 fe e t h ig h , a n d n o a l titu d e of m u c h m o re th a n 17,000 fe e t h a s b e e n re c o rd e d b y th e u se of a b a r o m e tr ic a ltim e te r o n a h ig h p e a k .) P e n d in g th e d e v e lo p m e n t of a n “ a b s o lu te a ltim e te r ,’’ w h ic h w ill te ll in s ta n ta n e o u s ly th e d is ta n c e b e tw e e n a p la n e a n d th e g ro u n d , i t seem s p ro b a b le t h a t a ir tr a v e l c a n b e s t be e x p e d ite d a n d m a d e s a fe r b y a c a re fu l s tu d y of b a ro m e tric c o n d itio n s in th e m o u n ta in s a lo n g th e re g u la r co u rse, a n d th e in s ta lla tio n of se v e ra l ra d io -e q u ip p e d w e a th e r s ta tio n s in th e a re a s of g r e a te s t b a r o m e tr ic d is tu rb a n c e . T h e s e s ta tio n s ca n b r o a d c a s t in f o rm a tio n to p la n e s a t s h o r t in te rv a ls , w a rn in g a g a in s t p o te n tia l in a c c u ra te a ltim e te r in d ic a tio n s , a n d s u p p ly ­ in g local c o rre c tio n s to n e a r b y p la n e s w h e n n ee d ed . T h is sh o u ld be a n im p r o v e m e n t o v e r th e p re s e n t p ra c tic e of u sin g a n a ltim e te r c o rre c te d fo r p re ssu re a t a la n d in g field o n o ne sid e of a ra n g e w h ile fly in g o v e r a reg io n w h o se w e a th e r m a y b e a r n o re la tio n to t h a t fo r w h ich th e a ltim e te r is a d ju s te d .

R onald

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L.

Iv es.

[J. F . I.

A CK N O W L ED G M EN TS.

A c o m p le te lis t of th o s e w h o h a v e g iv e n a s s is ta n c e in th e co lle c tio n of th e s e d a t a , a n d in th e p r e p a r a tio n of th is p a p e r, w o u ld fill se v e ra l p a g e s o f fine p r in t, a n d w o u ld in c lu d e p eo p le in s u c h v a r y in g so c ia l a n d in te lle c tu a l s t r a t a a s a n illite r a te I n d ia n s h e e p h e rd e r a n d a fo rm e r h e a d of th e U . S. W e a th e r B u re a u . T o th e la rg e n u m b e r of ra n c h e r s , m in e rs, lin e m e n , s m a ll-to w n te le p h o n e o p e r a to r s a n d r u r a l m a il c a r rie rs w h o a s s is te d in th e g a th e r in g a n d c h e c k in g o f in f o r m a ­ tio n , th e w r ite r e x p re sse s h is a p p r e c ia tio n . S p e c ia l m e n tio n is d u e D r. a n d M rs. C h a s . E . S n o w , of L a k e w o o d , C olo., fo r a s s is ta n c e in th e field ; th e G re e n m a n •S to re s C o., of B o u ld e r, C o lo ra d o , fo r s e c u rin g s p e c ia l ite m s of e q u ip m e n t a n d fo r s to r in g in fra -re d film s in t h e ir r e f r ig e r a to r on s e v e ra l o c c a sio n s; M r. C h a s. F . S n o w , of B o u ld e r, C o lo ., fo r a d v ic e a n d a s s is ta n c e w ith d iffic u lt p h o to g r a p h ic p ro b le m s , a n d th e C o lo ra d o M o u n ta in C lu b fo r ac c e ss to n u m e ro u s re c o rd s a n d p h o to g r a p h s . T h e w r ite r is e s p e c ia lly in d e b te d t o th e U . S. W e a th e r B u r e a u fo r in f o rm a tio n ; to th e U n iv e r s ity o f C o lo ra d o fo r th e use of n u m e ro u s b a r o g r a p h a n d th e r m o g r a p h tr a c e s ; to v a r io u s m e m b e rs of th e U . S. G eo lo g ica l S u r v e y fo r r e p o r ts of w e a th e r c o n d itio n s in th e m o u n ta in s , a n d to D rs . W . J. H u m p h r e y s a n d A . H . T h ie s s e n fo r v a lu a b le d is c u s s io n s o f th e p h e n o m e n a e n c o u n te re d in th e field. B IB L IO G R A PH Y A N D

N O TE S.

1. H e a t o n , R . L ., A n cestra l R o c k ie s a n d M eso z o ic a n d L a te P a leo z o ic S tr a ­

tig r a p h y o f R o c k y M o u n ta in R eg io n , B u ll. A m e r. A s s n . P e tr . Geol., 17, 1 9 3 3 , P P- 1 0 9 -1 6 8 .

2. A t w o o d , W . W ., a n d A t w o o d , W . W ., J r ., W o rk in g H y p o th e s is fo r th e P h y sio g ra p h ic H isto r y o f th e R o c k y M o u n ta in R e g io n , B u ll. Geol. Soc. A m e r., 4 9 , 1938, pp. 9 5 7 -9 8 0 . 3 . I v e s , R . L ., G lacial G e o lo g y o f th e M o n a rch V a lle y , G rand C o u n ty , C olorado, B u ll. Geol. Soc. A m e r., 4 9 , 1938, p. 1046—1065. 4. S p r a g u e , A b n e r , H ig h R a n g e s In flu en ce P a rk W e a th e r , E ste s P a r k T ra il, A pril 22, 1938, p. 22. 5. I v e s , R . L . , O p. c it.,z p. 1 0 6 3 . 6 . I v e s , R . L . , C h in o o k W in d s in N o r th e r n C olorado, A m e r. J o u r. S c i., V ol. X X X V , 1938, pp . 1 3 8 -1 4 2 . 7. C l e m e n s , S a m u e l ( M a r k T w a i n ) , R o u g h in g I t, N e w Y o r k , 1871, pp. 14 6 -1 4 8 .

D ec., 1938.]

9. 10. 11. 12. 13. 14.

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Q u i l l , D a n , T h e B ig B o n a n za , S an F ra n cisco , 1877, p. 106. N ote: T h e se tw o p op ular w riters d escrib e th e W a sh o e Z ep hyr in a so m ew h a t im p ression ­ istic m an ner, h a v in g m ore litera ry th a n scien tific m erit. H a s t i n g s , C. S ., A G en eral T h e o ry o f H a lo s, M o n th ly W eather R eview , 48, 1920, pp . 3 2 2 -3 3 0 . W o o l a r d , E . W ., T h e B ou ld er H a lo o f J a n . 10, 1918, M on th ly W eather R eview , 4 8 , 1920, pp. 3 3 1 -3 3 2 . H u m p h r e y s , W . J ., P h y sic s o f th e A ir, N e w Y o rk , 1929, pp . 5 1 9 -5 2 7 . A sep a ra te paper, d escrib in g th ese sto rm s in d e ta il, is c o n te m p la te d . I v e s , R . L ., O p. c it .,3p. 1061. I v e s , R . L ., O p. c it .,3p. 1064. H u m p h rey s, W . J ., O p. c it .,9pp . 291—292. S t e a r n s , J. C ., T h e M o u n t E v a n s L aboratory, S ci. M o ., V ol. X L V I , 1938, p p . 2 4 2 -2 4 8 . D e

8.

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T o p ic s .

[J. F. I.

N ew In d u strial U ses for F arm Crops.— D r . H . E . B a r n a r d . (.Refrigerating Engineering, Vol. 36, No. 3.) In his p ap e r p resen ted a t th e m eeting of th e A .S .R .E ., Dr. B arn ard , of th e N atio n al F arm C hem urgic Council, sta te d th a t to th e chem ical engineer th e farm er is essentially a m anufacturer, for he produces m aterials th a t, in th e n o t so d ista n t future, will provide not only a p ractical an d p e rm a n e n t cure of the farm problem b u t by m eans of p ro p er processing will give to th e consum er new and b e tte r goods. A lread y th e p ro g ram is u nder w ay, as is evident from view ing a n u m b e r of in d u stries. T he plastic in d u stry is one of th e faste st grow ing of th e chem ical industries. I t uses a g rea t v arie ty of raw m aterials p ro d u ced on th e farm , casein and soybeans, cotton or w ood pulp an d acetic acid w hich form cellulose acetate, and glycerine, a b y p ro d u c t of th e soap or oils and fats industries, w hich is th e basic m aterial in th e new G ly p to l resins. S tarch from th e sw eet p o ta to is a n o th e r exam ple. C o rn ­ starch is a basic m aterial essential in a g rea t n u m b er of industries and will become equally im p o rta n t in others. T h e in d u stria l chem ­ ist is m aking products of far g reater value th a n corn has ev er h ad on th e farm for a g rea t v arie ty of industrial needs. T h e use of corn sugar or dextrose is increasing rapidly. T h e conversion of farm p roducts into alcohol m ay well replace fuel w hich is now o b tain ed from a steadily decreasing production of our oil fields. S ugar, too, is a highly valued product. I t m ay well be th a t in th e y ears to com e our co u n try will be on an entirely self-supporting su g ar basis. I t could easily absorb th e sugar m ade from beets grown on 2,000,000 additional acres. N one of th e chem urgic rem edies will cure ag ri­ cultural ills or effect quick cures. N one will p u t th e p a tie n t on his feet unless he is willing to do his full p a r t in th e trin ity of ag ricu ltu re, in d u stry , and science. R . H . O.