TABLE OF CONTENTS

Summary

I n t r o d u c t i o n

S u r f a c e Winds

D i u r n a l Wind-Regime A l o f t a t Uc3A

Average Diurnal-Wind Time-Section a t u(IIA

Areal P a t t e r n on an I n d i v i d u a l B y

Ref e rence s

F i g u r e Number

1

2

4

5

6

7

8

9

10

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12

LIST OF FIGURES T i t l e

Page

1

1

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1 1

D i u r n a l Changes o f S u r f a c e Winds i n t h e IDS Angeles Bas in , August 1944

P r e v a i l i n g - W i n d Flow a t Hour o f Maximum Sea -Breeze Development ( L a t e A f t e r n o o n ) , o v e r Los Angeles Basin, August 1944

Sample Wind Time-Sect ion, U M , 1944

1 September

Time S e c t i o n o f w i n d s above KIA, u s t 1944

18-29 Aug-

Time S e c t i o n o f Winds above U a , 30August- 10 September 1944.

Predominant D a i l y Winds a t U U A

Wind-Direct ion Frequency Roses-- a. 14 Aug. 17 Sep 1944 0300-1100 PWT b. n 1300-1700 PWT

n 1900-2400 PWT C.

Wind-Direct ion Frequency R o s e s - U a a. 18 Sep-20 Nov. 1944 0300-0900 pwf

n 1100-1500 m b. n 1700-2400 PWT C .

Wing-Di r e c t i q n Frequency R o s e s - m 0500-0900 PWT a. 8-31 Jan. 1945

b. n 1100-1500 PRT n 1700-,1900 PWT C.

Wind Time-Sect ions a t V a r i o u s S t a t i o n s 5-6 September 1944 Oxnard, UUA, Mines F i e l d .

Wind Time-Sect ions a t V a r i o u s S t a t i o n s 5-6 September 1944 VanNuys, Cal. Tech, 9ntario.

P r o f i l e s of Land and Sea Winds a t V a r i o u s Hours . Los A n g e l e s B a s i n , 5-6 Sep tember 1944

1 3 Upper-Air Charts, 5-6 September 1944.

STRUCTURE OF THE LOCAL WINDS IN THE LOS ANGELES BASIN

SUMMARY

From a l a r g e number of s low-ascent p i l o t - b a l l o o n o b s e r v a t i o n s t h e t h r e e - d i m e n s i o n a l s t r u c t u r e i n t i m e o f t h e s e a a n d l a n d b r e e z e r e g i m e i s d e s c r i b e d f o r t h e Los Angeles Basin, C a l i f o r n i a .

The s e a b r e e z e i s d i r e c t e d a p p r o x i - m a t e l y p e r p e n d i c u l a r t o t h e l o c a l c o a s t l i n e b u t f o l l o w s up t h e tha lweg of i n l a n d v a l l e y s .

The s e a b r e e z e t e n d s t o merge i n t h e l o w e s t l e v e l s w i t h v a l l e y w i n d s , and t h e l a n d b r e e z e w i t h mounta in winds. The s e a - l a n d b r e e z e r e g i m e i s c o n f i n e d t o t h e c o a s t a l p l a i n west of t h e c o a s t a l mounta in range , b u t f l ows th rough t h e m o s t w e s t e r l y pas ses and i s f e l t by s t a t i o n s j u s t east of t h e s e pas ses .

At h i g h e r l e v e l s t h e r e i s a t endency f o r t h e s e a - l a n d breeze p a t t e r n t o merge w i t h t h e o c e a n - c o n t i n e n t w i n d s which a r e c o n t r o l l e d by t h e t h e r m a l l o w o v e r t h e sou thwqs te rn desert. When t h e t h e r m 1 l o w p e r s i s t s b o t h n i g h t a n d d a y f o r s h o r t p e r i o d s o f t i m e a n d i s s t r o n g e v e n a t l e v e l s u p t o 5000 f e e t , t h e o c e a n - c o n - t i n e n t regime approaches t h e c h a r a c t e r of a t r u e monsoon. However, when t h e l a n d wind i s s t r o n g it s e p a r a t e s t h e s e a b r e e z e i n t h e lower l a y e r s from t h e w e s t e r l y ocean- c o n t i n e n t wind by a l a y e r of e a s t e r l y l a n d winds.

When a h i g h p r e s s u r e c e n t e r a l o f t c e n t e r s over t h e G r e a t Basin, e a s t e r l y f low d u e t o t h e g e n e r a l c i r c u l a t i o n may merge wi th t h e land wind and conf ine t h e w e s t e r l y s e a b r e e z e t o a s m a l l d e p t h a n d s h o r t d u r a t i o n .

The c o m b i n e d s e a - v a l l e y b r e e z e i s f i r s t n o t i c a b l e n e a r t h e c o a s t and makes i t s a p p e a r a n c e p r o g r e s s i v e l y i n l a n d . I t deepens d u r i n g t h e c o u r s e of t h e a f t e r n o o n a t a l l s t a t i o n s and r eaches a g r e a t e r d e p t h i n summer than i n . w in te r .

T h e c o m b i n e d l a n d - m o u n t a i n w i n d appears f i r s t a t s t a t i o n s a l o n g t h e mountain s l o p e s n e a r t h e coast and p r o g r e s s i v e l y a f - f e c t s s t a t i o n s more i n l a n d . A t t imes i t a p p e a r s l a s t a t t h e c o a s t a l s t a t i o n s . I t deepens f a s t e r i n l a n d t h a n a t t h e i m e d i - a t e coast.

Average-wind t i m e - s e c t i o n s - a r e p r e - s e n t e d f o r one s t a t i o n f o r e a c h of t h e s e a s o n s : s u m m e r , f a l l a n d w i n t e r .

INTRODUCTION The c o o p e r a t i v e i n v e s t i g a t i o n of

c o a s t a l s t r a t u s i n s o u t h e r n C a l i f o r n i a du r - i n g t h e summer of 1944 (1) emphas ized t h e importance of t h e sea - l and b reeze regime a s a f a c t o r i n f l u e n c i n g t h e l o c a l w e a t h e r . The d i u r n a l o s c i l l a t i o n o f t h e h e i g h t of t h e s u b s i d e n c e i n v e r s i o n was f o u n d t o b e e x p l a i n e d ,in l a r g e p a r t by t h i s c o a s t a l wind p a t t e r n . Dur ing t h e s t r a t u s i n v e s t i - g a t i o n a l a r g e amount of w ind d a t a w e r e c o l l e c t e d and augmented by a d d i t i o n a l ob- s e r v a t i o n s i n t h e l a t e f a l l a n d w i n t e r . T h e s e d a t a c o n s t i t u t e t h e b a s i s f o r t h e p r e s e n t rctport. I t is conce rned p r i m a r i l y w i t h a d e s c r i p t i o n of t h e s e a - l a n d b r e e z e regime i n t h e Los Angeles Basin. A d i s c u s - s i o n o f some r e l a t e d w e a t h e r phenomena and t h e r e s u l t s of a t t e m p t s t o f o r e c a s t t h e b e g i n n i n g and e n d of , t h e s e a b r e e z e on p a r t i c u l a r days w i l l be c o v e r e d i n a l a t e r paper.

Most of t h e d a t a were c o l l e c t e d by t h e Army Weather S t a t i o n a t t h e U n i v e r s i t y o f C a l i f o r n i a a t Los Angeles ( V U ) by means of s low - a s c e n t p i 1 o t - b a 11 o ons wh i c h a 1 1 ow- e d o b s e r v a t i o n s t o be t aken a t v e r t i c a l in-5 t e r v a l s o f abou t IS0 f e e t . The p e r i o d s of o b s e r v a t i o n s were 1 5 August t o 20 November 1944 d u r i n g which 570 a s c e n t s w e r e observed, a n d 8 t o 3 1 J a n u a r y 1945, 149 a s c e n t s . Each a s c e n t was run t o 5000 f e e t i f circum- s t a n c e s a l lowed, which c o n s t i t u t e d approxi - m a t e l y 30 r e a d i n g s t a k e n a t i n t e r v a l s o f e i t h e r 2 5 or 30 s e c o n d s . I n a d d i t i o n , a n a l y s e s were made of t h e o r d i n a r y p i l o t - b a l l o o n d a t a and s u r f a c e w i n d s f o r s u r - round ing s t a t i o n s . Of p a r t i c u l a r i m p o r t - a n c e i s t h i s s t u d y were t h e Rawin d a t a t aken a t Mines F i e l d (XA) which i s l o c a t e d n i n e m i l e s SSE of UCLA.

The d e s c r i p t i o n o f t h e wind p a t t e r n s n e c e s s i t a t e d some d i s c u s s i o n o f p o s s i b l e c a u s e s o f o b s e r v e d phenomena i n o r d e r t o s e t up a nomenclature t o be usedo It i s n o t presumed t h a t t h e p r e s e n t r e p o r t is a

' d i s c u s s i o n o f a l l f a c t o r s r e l a t e d t o a c o m p l e t e s y n o p t i c d e s c r i p t i o n of t h e wind regime. However, t h e p r e s e n t a t i o n of b a s i c d a t a i n o r g a n i z e d form is one of t h e p r e -

8 1

l i m i n a r y s t e p s toward t h e comple t e unde r - s tanding .

t y p i c a l of t h e summer c o n d i t i o n s with l i t t l e change i n t h e g e n e r a l c i r c u l a t i o n from day t o day. Space l i m i t a t i o n r e q u i r e d t h e use o f c a l l l e t t e r s t o i d e n t i f y s t a t i o n s o n some of t h e f i g u r e s . T h e s e a r e l i s t e d , t o g e t h e r w i t h s t a t i o n e l e v a t i o n s , i n T a b l e 1 below.

I n t h i s r e p o r t t h e s e a - l a n d w i n d regime i s d e f i n e d a s a d i u r n a l o s c i l l a t i o n of d i r e c t i o n a t any l e v e l due t o the e f f e c t of t h e l and- sea t e m p e r a t u r e d i f f e r e n c e . A d i u r n a l change i n wind d i r e c t i o n i n the Los Angeles Bas in is found bo th below and above t h e t e m p e r a t u r e i n v e r s i o n w h i c h i s a c h a r a c t e r i s t i c of t h e summer i n t h i s a r ea . Below t h e i n v e r s i o n t h e mar ine s t r a t u m i s moist compared w i t h t h e a i r a l o f t , b u t i n t h e p r e s e n t d e f i n i t i o n , t h e s e a b r e e z e may o c c u r b o t h i n t h e l o w e r m o i s t and i n t h e upper d r y a i r .

TABLE I

CALL LETTERS AND STATION ELEVATIONS

call E l e v a t i o n Letters (Ft. m s l . ) S t a t i o n

Oceanside E l Tor0 (Marine Corps

Orange County Army Air

Long Beach Army Air

San Pedro (Naval Air

Lomita F l i g h t S t r i p US Angeles A i r p o i t

U n i v e r s i t y of C a l i f o r n i a

G l e n d d e (Grand C e n t r a l

Van M y s (Metropol i tan

Newha 11 Oxnard F l i g h t S t r i p Pasadena (CIT) O l t a r i o Army Air Field San B e m a r d i n 0 Army A i r

F i e l d R i v e r s i d e (March F i e l d ) Beaumont Palm S p r i n g s Army Air

F i e Id San N i c o l a s I s l a n d

(Naval Air S t a t i o n ) San Clemente I s l a n d

(Naval Air S t a t i o n ) Burbank (Lockheed Air

Terminal) Los Angeles (WW.B. C i t y

Off ice)

Air S t a t i o n )

F i e l d

Fie I d

S t a t i o n )

(Mines F i e l d )

a t Los Angeles

Terminal)

A i r p o r t )

oc 10 332 The v a l l e y - m o u n t a i n wind r e g i m e i s

s i m i l a r l y d e f i n e d a s a d i u r n a l o s c i l l a t i o n of d i r e c t i o n a t any l e v e l due t o t empera tu re d i f f e r e n c e s between t h e a i r over t h e v a l l e y a n d a i r o v e r t h e lower p l a i n . T h e % u p - v a l l e y wind i s t e r m e d s i m p l y t h e v a l l e y wind w h i l e t h e down-val ley wind i s c a l l e d t h e moun ta inwind . I n g e n e r a l , s l o p e or d r a i n a g e winds induced by t empera tu re d i f - f e r e n c e s between t h e f r e e a i r and t h e su r - f a c e of t h e mountain s l o p e s a r e cons ide red t o be p a r t o f t h e v a l l e y or mountain wind.

As w i l l be shown, most s t a t i o n s i n the Los A n g e l e s B a s i n e x p e r i e n c e w i n d s which c o n s i s t o f a merger of t h e s e a and v a l l e y b reezes or of t h e l a n d and mountain b reezes . S u r f a c e w i n d s o f t h i s t y p e , a s w e l l a s c a s e s when t h e t r u e c l a s s i f i c a t i o n c a n n o t be d e t e r m i n e d , w i l l b e t e r m e d t h e " s e a - v a l l e y " and "land-mountain" winds, r e s p e c t -

l i v e l y . S i n c e t h e s t u d i e s of t h e w i n d s aloft l a r g e l y i n v o l v e d o n l y s t a t i o n s near t h e c o a s t , where t h e l a n d and s e a b r e e z e s a r e t h e p r i m a r y e f f e c t s , t h e t e r m " s e a breeze" when a p p l i e d t o winds above t h e s u r - f a c e w i l l b e u n d e r s t o o d t o i n c l u d e a n y e f f e c t s of t h e v a l l e y wihd. S i m i l a r l y t h e t e r m " l a n d b r e e z e " , when a p p l i e d t o t h e u p p e r a i r w i l l i n c l u d e m o u n t a i n w i n d s .

P a c i f i c War Time i s u s e d t h r o u g h o u t t h i s r e p o r t .

Dsw 52

HB 40

Ncx 10

106 96

505

46 2

7 97 9

DGX

DVN

1190 82

758 9 20

1098

1528 2592 420

NCB so5

NSA 906

7 25

5 12

SURFACE WINDS Wind d i r e c t i o n f r e q u e n c y r o s e s were

p r e p a r e d f o r 2 1 s t a t i o n s from t h e h o u r l y t e l e t y p e r e p o r t s . From t h e s e wind roses the p r e v a i l i n g wind d i r e c t i o n dur ing v a r i o u s p o r t i o n s of t h e d a y c o u l d be d e s c r i b e d . The s u r f a c e wind regime f o r each s t a t i o n i s summar ized i n F i g u r e 1 on which a r e i n - d i c a t e d t h e a v e r a g e t i m e o f b e g i n n i n g and e n d i n g of t h e p r e v a i l i n g d i r e c t i o n s . Any

GENERAL PICTURE

The d i u r n a l c h a n g e s i n t h e s u r f a c e w i n d s a t a number of s t a t i o n s i n t h e Los A n g e l e s B a s i n were s t u d i e d i n d e t a i l f o r t h e month o f Augus t 1944. Al though o n l y 3 1 d a y s were t h u s u s e d i n d e r i v i n g t h e averages , i t is b e l i e v e d t h a t t h i s month i s

2

hours not i nc luded i n the s t a t i o n m o d e l may be c o n s i d e r e d t o b e t i m e s of v a r i a b l e wind d i r e c t i o n , u s u a l l y t h e t r a n s i t i o n f r a n one r e g i m e t o a n o t h e r , The B e a u f o r t f o r c e s g i v e n by t h e b a r b s on t h e a r rows r e p r e s e n t t h e average maximum d a i l y speeds .

Some e x p l a n a t i o n of t h e c r i t e r i a u sed t o d e c i d e when a wind i s p r e v a i l i n g may be d e s i r a b l e . A c e r t a i n amount of s u b j e c t i v e i n t e r p r e t a t i o n o f t h e wind r o s e s was r e - q u i r e d . In g e n e r a l , however, i f t h e p e r - c e n t a g e of w i n d s f r o m a p a r t i c u l a r 4 5 O s e c t o r was more t h a n t w i c e t h e p e r c e n t a g e f rom any o t h e r 45' s e c t o r (or ca lms) t h e d i r e c t i o n r e p r e s e n t e d by t h e c e n t e r of t h i s 4 5 ' s e c t o r was c o n s i d e r e d a " p r e - v a i l i n g " wind a t t h a t h o u r . T h i s d e f i - n i t i o n p e r m i t t e d t h e a n a l y s i s o f t h e n i g h t b r e e z e s wh ich u s u a l l y showed r a t h e r low f requeiicies b u t were n e v e r t h e l e s s a p p a r e n t b e c a u s e of t h e e v e n d i s t r i b u t i o n o f t h e o t h e r i i r e c t i o n s . A l l ca lms i n d i c a t e d a s " p r e v a i l i n g " i n F i g u r e 1 r e p r e s e n t e d o v e r 50% of t h e o b s e r v a t i o n s f o r t h e hours given.

The d a i l y s e a b r e e z e was a p p a r e n t a t a 1 1 s t a t i o n s i n t h e b a s i n . I n a d d i t i o n , a l i g h t l a n d or m o u n t a i n b r e e z e was ob- s e r v e d a t most s t a t i o n s d u r i n g t h e n i g h t . I n marly c a s e s , h o w e v e r , t h e e f f e c t s of m o u n t , i i n a n d v a l l e y b r e e z e s a r e q u i t e d i f f i c u l t t o s e p a r a t e from t h e s e a and l and b r e e z e c i r c u l a t i o n , s i n c e b o t h t e n d t o move i n s i m i l a r d i r e c t i o n s . A l l s u r f a c e w i n d s a r e i n f l u e n c e d m a r k e d l y b y t h e topography, e v e n t h e lowes t h i l l s p l a y i n g a not i :eab le p a r t i n t he summer c i r c u l a t i o n H i l l s l ower t h a n 1000 f e e t c o u l d - n o t be shown i n F i g u r e 1 b u t t h e i r e f f e c t w i l l be mentioned i n t h e d i s c u s s i o n s . For a more d e t a i l e d map o f t h e topography of t h e Los A n g e l c s B a s i n t h e r e a d e r i s r e f e r r e d t o F igurc : 2, t a k e n f rom t h e r e p o r t of C a l i - fokn i s . S t r a t u s I n v e s t i g a t i o n of 1944 (1) *

' h e d a y t i m e wind reg ime i s i n d i c a t e d b y t h e s o l i d a r r o w s i n F i g u r e 1 . Wind d i r e c t i o n s c h a r a c t e r i s t i c o f t h e l a t e a f t e r n o o n a r e shown w i t h h e a v i e r l i n e s . T h e s e s h o u l d r e p r e s e n t t h e f l o w n e a r t h e t i m e of maximum s e a b r e e z e , which i s a l s o shown by t h e s t r e a m l i n e s i n F i g u r e 2 , I t i s i m m e d i a t e l y a p p a r e n t f r o m t h e ov p i c t u r e of t h e a f t e r n o o n s e a b r e e z e the. f l o w of a i r comes onshore approximate ly p e r p e n d i c u l a r t o t h e l o c a l c o a s t l i n e , b u t once .Inland is g u i d e d up the main v a l l e y s toward t h e p a s s e s . The f l o w s p l i t s i n t o t w o mi in s t r e a m s , a s c a n be c l e a r l y s e e n on Figure 2.- One s t r e a m f l o w s no r theas tward i n t o t h e San Fernando V a l l e y where Burbank (BU) and Van Nuys M e t r o p o l i t a n A i r p o r t ( D W a r e l o c a t e d , t h q o t h e r e a s t w a r d to-

ward San G o r g o n i o P a s s i n which Beaumont (TUT) i s l o c a t e d . The s e a - v a l l e y wind reg ime i s f e l t a t Palm S p r i n g s (IIPZ) e a s t of t h e San Gorgon io P a s s and 80 m i l e s i n - l a n d f rqm t h e c o a s t , and s l i g h t l y a f f e c t s t h e w i n d s a t S a n C l e m e n t e I s l a n d (NGA), 60 m i l e s o u t t o s e a . San N i c o l a s I s l a n d (-1, 80 miles from t h e c o a s t , a p p a r e n t l y i s n o t s u b j e c t t o the d i u r n a l s h i f t s of t h e land-sea b reeze regime,

The e f f e c t o f t h e " C a t a l i n a Eddy" i s a p p a r e n t i n t h e change from p r e v a i l i n g Nw winds a t San M i g u e l I s l a n d ( n o t shown i n F i g u r e 1 b u t abou t 80 m i l e s NW of NCB) t o

WNW winds a t NQB and t o WSW winds a t %A. lhis appea r s t o *be a semi-permanent f e a t u r e of t h e c i r c u l n t i o n r a t h e r t h a n a d i u r n a l 2 f f ec t.

The no r the rnmos t s t r e a m l i n e i n F i g u r e 2 , r e p r e s e n t i n g w e s t e r l y f l o w o v e r UCLA, t u r n s i n t o a s t r e a m o v e r t h e S a n t a Monica mounta ins a t Cahuenga P a s s a b o u t 5 m i l e s wes t of t h e Los A n g e l e s R i v e r . T h i s h a s b e e n v e r i f i e d b y " t r a j e c t o r y b a l l o o n s " r e l e a s e d a t UCLA. T h e s e b a l l o o n s were i n f l a t e d t o a ve ry sma l l o r z e r o f r e e l i f t , r e l e a s e d , and o b s e r v e d w i t h t h e o d o l i t e s . @ l y a v e r y f e w r u n s were made b u t some b a l l o o n s were o b s e r v e d t o r e t u r n up t h e San F e r n a n d o V a l l e y t o t h e m e r i d i a n o f UCLA a f t e r p a s s i n g o v e r Cahuenga P a s s . The s t r o n g s u b s i d e n c e i n v e r s i o n , combined w i t h t h e n e g l i g i b l e f r e e l i f t , s u c c e e d e d i n k e e p i n g most of t h e b a l l o o n s t o e l e v a - t i o n s below 2500 f e e t .

I t w i l l be n o t e d f r o m F i g u r e 1 t h a t t h e n i g h t w i n d s shown i n d o t t e d a r r o w s a re p r e s e n t a t n e a r l y a l l s t a t i o n s a s f a r i n l a n d a s March F i e l d (RV) and seaward a s f a r a s San C lemen te I s l a n d . T h e s e n i g h t

w i n d s a r e , however , w e a k e r t h a n t h e s e a b reeze a t a l l s t a t i o n s .

The d e t a i l s of t h e d i u r n a l r e g i m e s a t v a r i o u s s t a t i o n s a r e more c o m p l i c a t e d t h a n t h e g e n e r a l p i c t u r e j u s t d e s c r i b e d .

SFA AND V A U E Y BREEZES

(a) ?he sea breeze and the effect o f v a l l e y winds . - A t some s t a t i o n s a w e s t e r l y wind b e g i n s two or t h r e e h o u r s a f t e r sun- rise (about 0620 i n August) bu t comes from a d i r e c t i o n s l i g h t l y d i f f e r e n t f rom t h a t of t h e m a x i m u m sea b reeze . T h i s e a r l y wind can u s u a l l y be i n t e r p r e t e d a s a v a l l e y wind w h i c h coinmences e a r l i e r t h a n t h e more gene ra l s ea breeze . .

3

E v i d e n c e of t h e v a l l e y wind merging i n t o a s e a b r e e z e i s a l s o p r o v i d e d by t h e f a c t t h a t t h e w e s t e r l y s e a - v a l l e y wind b e g i n s e a r l i e s t a t s t a t i o n s l o c a t e d on a n,qrrow c o a s t a l p l a i n . R a p i d h e a t i r l g of t h e mountain s l o p e s would c a u s e t h e v a l l e y b r e e z e t o s t a r t p r i o r t o t h e s e a b r e e z e i n t h e s e cases .

A n a l y s i s o f t h e d i u r n a l c h a n g e s a t O r a n g e C o u n t y Army A i r F i e l d (DSW) i s t y p i c a l of t h e r e a s o n i n g which may be ap- p l i e d t o many o t h e r s t a t i o n s . The s e a - v:tlley b r e e z e beg ins a t about 0930 from t h e W S W a n d b a c k s g r a d u a l l y t o SW by 1430. T ? i s c h a n g e o f d i r e c t i o n i s o p p o s i t e t o t h a t which would be e x p e c t e d a s t h e r e s u l t of t h e a p p r o a c h o f a t r u e s e a b r e e z e t o ba l anced flow. Dur ing t h e p r o g r e s s of t h e day t h e C o r i o l i s f o r c e would t e n d t o pro- dilce v e e r i n g of wind a t c o a s t a l s t a t i o n s . The WSW wind a t t h e t i m e o f o n s e t may be r ega rded , however, a s t h e v e c t o r sum of a 9Y s e a b r e e z e p e r p e n d i c u l a r t o t h e c o a s t , and P W breeze blowing i n t o t h e v a l l e y e a s t 01' Santa Ana which can be seen i n F i g u r e 2. The s e a b reeze e f f e c t i n c r e a s e s a s t h e day p rogres ses , becoming predominant by 1430 and c i m t i n u i n g u n t i l two h o u r s a f t e r sun ' se t .

In g e n e r a l , t h e speed a t t a i n e d by t h e s e a - v a l l e y b r e e z e a p p e a r s to be n e a r l y t h e same a t a l l s t a t i o n s . S i n c e a t r u e s e a breeze s h o u l d d imin i sh i n speed f a r t h e r in - hind it i s aga in appa ren t t h a t a merging of t h e s e a b r e e z e i n t o t h e v a l l e y wind t a k e s p l a c e . N o t i c a b l e i n c r e a s e s i n s p e e d a t a f t w s t a t i o n s ( e . g . , IX)I, IW, RQ a r e pro- b:ibly t h e r e s u l t o f c h a n n e l i z a t i o n of t h e f l o w by t o p o g r a p h y r a t h e r t h a n t h e r m a l elc f e c t s .

I t w i l l a l s o be n o t e d t h a t t h e o n s e t O F t h e s e a - v a l l e y b reeze a t i n l and s t a t i o n s s u c h a s Newhal l (NH) and March F i e l d (RVI occur s on ly one or t w o hour s l a t e r than a t t he c o a s t a l s t a t i o n s . 'Ihis i s i n s u f f i c i e n t t i m e f o r t h e a i r which crossed t h e c o a s t t h e r e a t t h e o n s e t of t h e s e a b r e e z e t o hive r eached t h e i n l a n d s t a t i o n s , even i f tile s e a a b r e e z e f r o n t moved w i t h t h e s p e e d of t h e sea wind. M o i s t u r e c o n t e n t of t h e a i r i s , t h e r e f o r e , n o t a c h a r a c t e r i s t i c of t h e s e a - v a l l e y b r e e z e i n t h i s r e p o r t . Fi-esh mar ine a i r w i l l , of cour se , be c a r r i e d i n l a n d by t h e s e a b r e e z e l a t e r i n t h e day, b u t t h e change of wind d i r e c t i o n may occur s e v e r a l h o u r s b e f o r e the a r r i v a l of t h e new a i r a t t h e i n l a n d s t a t i o n s .

01 days when a n o f f - l a n d p r e s s u r e g r a - d i e n t e x i s t s t h e pas sage of t h e s e a - b r e e z e " f r o n t " f r e q u e n t l y h a s been o b s e r v e d a t

4

s t a t i o n s n e a r t h e c o a s t . Under such con- d i t i o n s n o t i c e a b l e changes i n both temper- a t u r e a n d m o i s t u r e o c c u r s i m u l t a n e o u s l y w i t h t h e wind s h i f t . T h i s e f f e c t may b e q u i t e s t a r t l i n g a t l o c a t i o n s w i t h i n a b o u t a m i l e o f t h e s h o r e , when t h e p r e v i o u s l y i n a u d i b l e r o a r of the s u r f s t r i k e s t h e e a r s of t h e o b s e r v e r .

(b) E f f e c t s o f the San F e r n a n d o V a l l e y . - The r e v e r s a l o f wind a t Newhal l 0 a t 1100 may be e x p l a i n e d a s t h e change from a l i g h t n o r t h w e s t e r l y b r e e z e b lowing up t h e S a n t a C l a r a Canyon t o t h e s t r o n g s o u t h e a s t e r l y s e a - v a l l e y b r e e z e caning ove r Newhal l P a s s from t h e San Fernando V a l l e y ( s e e F i g u r e 1). I t i s i n t e r e s t i n g t o n o t e t h a t t h e r e i s p r a c t i c a l l y no ev idence of a s e a b r e e z e r e a c h i n g NH by way of t h e S a n t a C l a r a V a l l e y . T h i s wou ld be a r o u t e of n e a r l y t h e same l e n g t h a s t h e t r a j e c t o r y f o l l o w e d i n p a s s i n g u p t h e S a n F e r n a n d o V a l l e y . The r e a s o n f o r t h e predominance of t h e l a t t e r f l o w p r o b a b l y l i e s i n t h e broader expanse of low e l e v a t i o n i n t h e San Fernando Va l l ey , wi th r e l a t i v e l y sma l l loss by d i v e r s i o n a s u p - v a l l e y w i n d s i n t o t h e h ighe r mountain ranges.

Flow i n t h e San F e r n a n d o Va l l ey a l s o u n d e r g o e s p e c u l i a r c h a n g e s e a r l y i n t h e evening, a d e f i n i t e s h i f t beginning a t sun- set (about 1945 i n August) . The e a s t e r - l y or s o u t h e a s t e r l y winds d u r i n g t h e f i r s t h a l f of t h e n i g h t , a l t h o u g h i n d i c a t e d a s n i g h t w i n d s i n F i g u r e 1 , seem t o b e a con t inua t i o n of t h e s e a b reeze .

A t l e a s t p a r t of t h e e x p l a n a t i o n of t h i s f l ow up t h e v a l l e y f o r a l a r g e p o r t i o n of t h e n i g h t must l i e i n t h e r e l a t i v e l y b r o a d e x p a n s e a n d g e n t l e s l o p e o f t h e v a l l e y . A c c o r d i n g t o t h e o r y based upon t h e German i n v e s t i g a t i o n s (2 ) , t h e t i m e r equ i r ed t o r e v e r s e from t h e v a l l e y b r e e z e to a mountain (down-valley) b r e e z e depends i n v e r s e l y u p o n t h e i n c l i n a t i o n o f t h e v a l l e y f l o o r . T h i s is because t h e a d i a b a t i c c o o l i n g p r o c e s s e s depend upon t h e amount of v e r t i c r l mo t ion which c a n t a k e p l a c e . The s t e e p i n c l i n a t i o n of t h e e a s t e r n s i d e of t h e San Fernando V a l l e y , a s w e l l a s t h e r a q d r a d i a t i o n a l c o o l i n g o f t h e h i g h mounta in a r e a s , p robab ly a c c o u n t s f o r t h e s h i f t t o more e a s t e r l y winds a t 2000. The smal l i n c l i n a t i o n of t h e v a l l e y f l o o r , how- ever , t e n d s t o r e t a r d t h e d i s a p p e a r a n c e of

r e v e r s e f low, A s i m i l a r e x p l a n a t i o n w i l l n o d o u b t account f0.r t h e l a t e ending of t h e s e a - v a l l e y b r e e z e a t March F i e l d (RV).

( c ) Effect o f the San Pedro H i l l s . -

the valley wind and the development of t h e

The Sari P e d r o Wil ls , wh ich s u r m o u n t t h e p o i n t o f land w e s t of San Pedro Bay, s e t up a s m a l l wave i n t h e s e a - b r e e z e c i r c u l a t i o n n e a r Long Beach a s can b e s e e n hy t h e wave i n t h e s t r eaml ines on F i g u r e 2. The s e a bree%e a t Long Beach (HB) b e g i n s from t h e SSE a t 1 0 0 0 , v e e r i n g g r a d u a l l y t o SSW by 1200, where i t remains u n t i l 1430. At San P e d r o (r4a) t h e s e a - v a l l e y b r e e z e comnences a t 0800 f rom' the SE, v e e r i n g g r a d u a l l y t o a s t e a d y '3SW b y 1100. Lomita F l i g h t S t r i p 0 took t h r e e - h o u r l y o b s c r v a t i o n s o n l y , so t h e times o f o n s e t and c e s s a t i o n of t h e predominant w i n d s a r e n o t i n d i c a t e d . A t 2330 a s o u t h e r l y d r a i n a g e - w i n d p r e v a i l s , c h a n g i n g t o SW a t 0230 a n d 05-30. T h e s t r o n g WNW sea b r e e z e i s prqdominant from 1130 tcl 2 0 3 0 . A wave i n t h e s t r e a m l i n e s o v e r San P e d r o Bay must t h u s o c c u r between 1000 and 1430. T h i s wave e i t h e r mows t o t h e s o u t h o r d e c r e a s e s c o n s i d e r a b l y i n ampl i tude by 1430 t o p e r m i t t h e a r r i v a l a t HB o f t h e WMni f l o w from S a n t a Monica Bay.

LAM) AND MOUNTAIN BREEZES

The l a n d b r e e z e i n t h e Los A n g e l e s B a s i n i s g e n e r a l l y f r o m t h e e a s t , t h a t i s i n t h e o p p o s i t e d i r e c t i o n f r o m t h e s e a b r e e z e . The l a n d b r e e z e , b e i n g g e n e r a l l y of smaller s p e e d , i s a f f e c t e d even more by t h e l o c a l topography. A f t e r t h e sea b r e e z e d i e s down, a p e r i o d o f v a r i a b l e w i n d o r calm u s u a l l y e n s u e s ) fol lowed by a d r a i n a g e o r moun ta in w i n d , l a t e r r e i n f o r c e d by a genera l e a s t e r l y l a n d breezer .

F3r e x a m p l e , a t O r a n g e C o u n t y Army A i r F i e l d (DSW) t h e p e r i o d o f calms o r v a r i a b l e s l a s t s u n t i l m i d n i g h t when a d e f i n i t e E wind b e g i n s , c o n t i n u i n g u n t i l the s e a b r e e z e s t a r t s a t 0930. The c o o l i n g mountam s l o p e s mad i fy a n y t e n d e n c y f o r a land breeze p e r p e n d i c u l a r t o t h e s h o r e l i n e . I t .is somewhat s u r p r i s i n g t h a t t h i s E wind c o n t i n u e s so l o n g a f t e r s u n r i s e (0620 l%T averag,: f o r Augus t ) w h i l e t h e s e a - v a l l e y breeze a p p a r e n t - l y s t o p s w i t h i n two h o u r s of sunsiet. T h e r e is a s l i g h t weakening o f t h e Ial ld-mountain b r e e z e a f t e r 0800 , w i t h s h i f t s t o NE a n d SE, b u t t h e g e n e r a l e a s t e r l y canponenit: predominates u n t i l 0930-

Evrdence t h a t t h e n i g h t t i m e s u r f a c e wind i s p r i m a r i l y de te rmined by t h e c o o l i n g of the mounta ins and t h e topography of t h e basin, rather than by t h e s e a - l a n d ternper- a ture d i f f e r e n c e , i s shown by t h e s t a t i o n s to t h e n o r t h a n d w e s t o f DSW, U U (PUC), Pasadena (WA)3 O n t a r i o (Tx)l) a n d Lomi ta m) !;how mounta in b r e e z e s d i r e c t l y o f f t h e s l o p e s behind t h e s t a t i o n s . At M e t r o p o l i - t a n A i r p o r t (DVN) i n t h e S a n F e r n a n d o

I I

V a l l e y a' l i g h t N wind h e g i n s a t 0100, A s i m i l a r downslope wind commences a t 0330 a t t h e Lockheed A i r Termina l (Ru) and a t about 0230 a t Grand C e n t r a l A i r T e r m i n a l (I=). h e t o i t s p o s i t i o n i n t h e na r row p a r t of t h e v a l l e y t h e f l o w a t I X X r e a c h e s g r e a t - er speeds than a t t h e o t h e r s t a t i o n s . This f l o w j o i n s a b r o a d e r e a s t e r l y f l o w which crosses t h e c o a s t a l o n g S a n t a Monica Ray. Cold a i r From t h e San Fe rnando V a l l e y may account f o r t h e n o r t h e a s t e r l y b e g i n n i n g of t h e l a n d b r e e z e a t Mines F i e l d (LA), t h e wind v e e r i n g g r a d u a l l y t o E a s t h e f l o w from t h e S a n t a Ana R i v e r b a s i n i n c r e a s e s . ?he s o u t h e a s t e r l y wind a t IDng Reach Army Air F i e l d (HB) d u r i n g t h e n i g h t a n d t h e e a s t e r l y f l o w a t Mines F i e l d (ui) seem t o i n d i c a t e t h a t S a o t a M o n i c a R a y i s a major o u t l e t o f t h e n i g h t w i n d s . The SE b r e e z e a t HB ( w h i c h - i s a c t u a l l y u p s l o p e ) n o doubt r e s u l t s f r a n t h e g u i d i n g e f f e c t o f S i g n a l B i l l a n d a d j a c e n t r i d g e s . T h i s c h a i n o f l o w h i l l s , w h i l e o n l y 200 t o 300 f e e t i n h e i g h t , e x t e n d s i n a NW-SEline j u s t t o t h e south of HB (F igure 2) . I f t h e major o u t l e t o f t h e l a n d b r e e z e were San P e d r o Bay t h e s e h i l l s s h o u l d d e f l e c t t h e f l o w i n t o a Mli r a t h e r t h a n a SE b r e e z e a t HB.

A t San Bernard ino (DJI,) t h e n i g h t wind appears t o come down t h e canyon of t h e S a n t a Ana R i v e r , canmencing a t midnight and s t o p - p ing soon a f t e r s u n r i s e . March F i e l d (RV) h a s a l i g h t n o r t h e r l y w i n d be tween 0100 and 0300 which changes r a t h e r a b r u p t l y t o a SE breeze . The n o r t h wind mav b e a mount- a i n b r e e z e o f f t h e r i d g e s t o t h e n o r t h o f the f i e l d , which r e a c h e l e v a t i o n s o f 3000 f e e t . T h i s is overcome a t 0300 by t h e more g e n e r a l dowh-val ley f low from t h e SE. The SE b r e e z e w e a k e ~ s s l o w l y a f t e r s u n r i s e u n t i l 0 9 0 0 , when a somewha t s t r o n g e r S wind b e g i n s . T h i s S wind i s p r o b a b l y t h e upslope wind c o r r e s p o n d i n g t o t h e n o r t h e r l y downslope b r e e z e between 0100 and 0300, A t 1100 t h e S wind i s r e p l a c e d by t h e s e a - v a l l e y b r e e z e , a m w i n d w h i c h r e a c h e s s p e e d s of 1 5 mph o r more by 1 7 3 0 and d i - m i n i s h e s g r a d u a l l y t h e r e a f t e r . By 2330 t h e Nw winds i s n o l o n g e r t h e predominant d i r e c t i o n a n d a s h o r t p e r i o d of c a l m s o r v a r i a b l e wind d i r e c t i o n s p r e v a i l s .

SPECZAL EFFECTS AT THE SAN GORGONIO PASS

aumqnt (WT-2592 f e e t ) , which l i e s i n the mouth of San Gorgon io Pass shows a d i u r n a l wind r eg ime q u i t e d i f f e r e n t f rom t h e o t h e r s t a t i o n s . The predominan t wind is n o t t h e s e a - v a l l e y b r e e z e b u t a l i g h t e r

wind which t a k e s o v e r as t h e sea b r e e z e

5

d r m i n i s h e s a r o u n d 2 2 0 0 . T h i s Nw w i n d r ema ins v e r y s t e a d y t h r o u g h o u t t h e n i g h t ( o v e r 7 0 % o f o b s e r v a t i o n s r e p o r t t h i s d i r e c t i o n ) , b u t a t 0 8 0 0 b e g i n s t o b a c k s j .owly , r e a c h i n g WSW by 1 1 3 0 , A t t h i s t i t m e t h e f u l l e f f e c t o f t h e s e a - v a l l e y b reeze h a s presumably reached t h e s t a t i o n . The s e a - v a l l e y breeze does no t remain s t eady from t h e WSW, however, b u t s h i f t s e r r a t i - c a l l y between WSW and%W d u r i n g t h e a f t e r - noon. T h i s is d o u b t l e s s a n a l t e r n a t i o n between f lows up one and t h e o t h e r s i d e of t h e r i d g e n o r t h o f March F i e l d . By 2100 t h e p e r s i s t e n t n o r t h w e s t e r l y f l o w b e g i n s to predominate and ve ry f e w s o u t h e r l y com- ponents occur a f t e r t h a t time.

f i r i n g the a f t e r n o o n t h e f low o v e r San Q)rgonio P a s s e x h i b i t s t h e c h a r a c t e r i s t i c s of what i s t e rmed t h e "Malo ja wind" (2 ) . A l t h o u g h t h e summit o f t h e p a s s i s n e a r Beaumont t h e s u r r o u n d i n g r i d g e s c o n t i n u e to r i s e f o r a n o t h e r 14 m i l e s t o t h e e a s t . %l i s f a v o r s t h e c o n t i n u a t i o n of t h e wes ter - l i t wind t h r o u g h t h e p a s s i n s p i t e o f t h e dc:scending v a l l e y f l o o r . Narrowing of t h e d l e y toward t h e e a s t and probably accourts f o r t h e h i g h s p e e d s o f t h e wind r e a c h i n g Rtlm Spr ings (m).

I t seems e v i d e n t t h a t d u r i n g t h e time the l i g h t e a s t e r l y s u r f a c e winds a r e f l o w - i r g a t DJL a n d RV, a n e n t i r e l y d i f f e r e n t f l o w i s p r e v a i l i n g a t TUT. A t 0300 a b o u t 7!;% of t h e s u r f a c e w i n d s a t TUT w e r e NW. The most f r e q u e n t wind d i r e c t i o n s r e p o r t e d a t t h e same t i m e by t h e p i b a l s t a t i o n s i n the v i c i n i t y a r e g iven i n Tab le 2.

These o b s e r v a t i o n s i n d i c a t e t h a t t h e n i g h t t i m e l a y e r o f e a s t e r l i e s must t h i n r a p i d l y t o w a r d t h e p a s s , a l l o w i n g a con- s t a n t f l o w o f t h e h i g h e r l e v e l wester l ies through t h e pass . A t t h e e a s t e r n o u t l e t o f t h e p a s s t h i s w e s t e r l y f l o w d i s a p p e a r s r a p i d l y b y m i x i n g i n t o a s o u t h e a s t e r l y flow o v e r Pa lm S p r i n g s , where t h e a i r re- mirs ca lm a t t h e s u r f a c e .

The 6 - h o u r i n t e r v a l be tween r e g u l a r p i b a l s i s t o o l o n g t o p r o v i d e d a t a f o r d e t a i l e d s t u d y of t h e d i u r n a l wind-changes a l o f t . S p e c i a l o b s e r v a t i o n s f o r t h i s purpose w i l l be d e s c r i b e d i n t h e f o l l o w i n g sec t ions .

DIURNAL WIND-REGIME ALOFT AT UCLA

The d i u r n a l w ind- reg ime o b s e r v e d a t U a i s s i m i l a r t o t h a t a t m o s t s t a t i o n s i n t h e a r e a , c o n s i s t i n g of a s e a breeze from t h e SW d u r i n g t h e a f t e rnoon and an e a s t e r l y o f f - l a n d wind du r ing t h e n i g h t .

To i l l u s t r a t e t h i s r e g i m e F i g u r e 3 p r e s e n t s a t ime-he ight s e c t i o n o f t h e winds o b s e r v e d a t UCLA on 1 S e p t e m b e r 1944. Though n o i n d i v i d u a l d a y shows a l l t h e f e a t u r e s o f t h e ave rage p i c t u r e , t h i s day d e m o n s t r a t e s some o f t h e p r e v a l e n t c h a r a c - t e r i s t ics o f t h e regime. B r i n g t h e p e r i o d f r o m m i d n i g h t t o noon t h e w i n d s a t t h e s u r f a c e and i n t h e l owes t 2000 f e e t were E o r SE a t s s a l l speeds , t y p i c a l of t h e o f f - l a n d n i g h t t i m e wind. A t noon t h e s u r f a c e w i n d v e e r e d t o S, t h e c h a r a c t e r i s t i c

TABLE 2

MAXIMUM DlRECTXON-FREQUENCIES FROM PIBALS AT 0 3 0 0 PWT 1 - 3 1 AUGUST 1944

S t a t ion

San Bernard ino @&) N N

W n

March F i e l d (RV) N n N n

n W

Palm Spr ings (mZ) n W

W n

Height Di rec t i .on* and Frequency (msl) Maximum Secondary Maximum

2500 40 00 SO00 2000 3040 4000 SO00 1200 2500 5000

*Direct ion g iven inc ludes winds 22 l/Zo on each s i d e .

6

SSE 43% S 41% W 58% E 29% E 53% WNW 33% W 40% SSE 3977 SSE 59% SE 57%

Nw 18% wsw 33% SW 42% SSW 29% w 35% SSW 24% ssw 2 5 % W 36$

UlNW 19% DE 26%

h a r b i n g e r o f t h e s e a b r e e z e . The SW s e a breeze was w e l l deve loped by 1330 below 2000 f e e t w h i l e t h e e a s t e r l i e s p e r s i s t e d i n a l a y e r a l o f t . The s e a b r e e z e d i s a p p e a r e d a t t h e s u r f a c e a t 2030 w h i l e s t i l l b lowing a l o f t . By s h o r t l y a f t e r midnight t h e wind i n t h e l a y e r from 1000 t o 2000 f ee t backed t o SE.

Dur ing t h e e n t i r e day t h e winds from 5000 t ( 2 10 ,000 f e e t were s t e a d i l y from t h e NW q u a d r a n t , t h u s emphas iz ing t h e r e a l i t y o f t h e e a s t e r l y wind i n t h e lowest l e v e l s . n o u g h o c c u r r i n g on many days , a l a y e r o f e a s t winds p e r s i s t i n g d u r i n g t h e e n t i r e d a y , :is i n t h e c a s e o f 1 S e p t e m b e r , i s by no means i n v a r i a b l e . The t i m e s e c t i o n h a s been a n a l y z e d t o show t h e s e p a r a t i o n of th t : e a s t e r l y f r o m t h e s o u t h w e s t e r l y w i n d s i n t h e l o w e r l e v e l s , a n d f rom t h e northwes t e r l i e s a l o f t .

?‘he d e l i n e a t i o n of a sea b r e e z e and a l a n d b r e e z e i s n o t a lways e a s y inasmuch as t h e r e i s a t r a n s i t i o n zone between t h e s ea b r e e z e , l a n d b r e e z e , a n d u p p e r f l o w c h a r a c t e r i z e d b y a g r a d u a l t u r n i n g o f wind w i t h h e i g h t . A s an example, a t 1500 PWT 1 S e p t e m b e r ( F i g u r e 3) t h e ESE w i n d s a t 2000 f’eet b a c k e d g r a d u a l l y t o Nw a t 8000 f e e t . I t i s c l e a r t h a t t h e e a s t e r l y w i n d s r e p r e s e n t e d t h e l a n d b r e e z e w h i l e t h e NW o r WNW w i n d s p r e d o m i n a t i n g a l o f t th roughout t h e day were p a r t o f t h e g e n e r a l

: c i r c u l a t i o n .

“The wind d i r e c t i o n i n t h e t r a n s i t i o n l a y e r c a n b e c o n s i d e r e d t h e v e c t o r re- s u l t a n t o f a n e a s t e r l y c o m p o n e n t , t h e l a n d - b r e e z e e f f e c t , and a m - w i n d v e c t o r r e p r e s e n t i n g u p p e r flow. n e i n c r e a s e o f t h e W e f f e c t w i t h h e i g h t and t h e d e c r e a s e o f e a s t e r l y component would p r o d u c e t h e o b s e r v e d b a c k i n g w i t h h e i g h t . A t wha t l e v e l t h e l a n d wind may b e c o n s i d e r e d t o e n d and t h e g e n e r a l c i r c u l a t i o n t o b e g i n mus t b e an a r b i t r a r y d e f i n i t i o n . Even i f a zone o f t r a n s i t i o n were o u t l i n e d a s a s e p a r a t e l a y e r , i t would b e n e c e s s a r y to se t up l i m i t s o f each zone on t h e b a s i s o f d i r e c t i o n .

]:or p u r p o s e s o f t h e wind t i m e - s e c t i o n s i n t h i s r e p o r t (e.g. Figures 4 and 5 ) , t h e d i v i s i o n l i n e s between l a n d wind and u p p e r f l o w l a v e been drawn t o i n c l u d e t h e winds f r o m SSE to NNE i n t h e l a n d - b r e e z e zone , and n o r t h w i n d s i n t h e u p p e r flow. T h i s is t h 2 same as s a y i n g t h a t t h e v e c t o r com- p o n e n t o f u p p e r f l o w i s c o n s i d e r e d t o p r e d o m i n a t e o v e r t h e e a s t e r l y Component when the wind h a s backed t o n o r t h . I t would p e r h a p s b e p r e f e r a b l e t o i n c l u d e i n t h e

l a n d wind z o n e a l l w i n d s wh ich show t h e e f f e c t o f a n y e a s t e r l y component. I t i s , h o w e v e r , f r e q u e n t l y i n i p o s s i b l e t o make such a d i s t i n c t i o n and f o r t h i s reason such 1 i n i i t s w e r e c o n s i d e r e d u n s a t i s f a c t o r y . Where t h e t r a n s i t i o n was n o t d i s t i n c t or where d a t a were i n s u f f i c i e n t t o p l a c e i t w i t h a c c u r a c y dashed l i n e s have been used.

The s e a b r e e z e , which i s o r d i n a r i l y SW, o f t e n v e e r s i n t o a NW f l o w a t h i g h e r l e v e l s i n t h e same manner t h a t t h e e a s t e r l y winds backed t h r o u g h N to W. The d i f f e r - e n t i a t i o n of t h e t o p o f t h e s e a breeze i s , t h e r e f o r e , a l s o a r b i t r a r y . I n t h e p r e s e n t a n a l y s e s o f t i m e s e c t i o n s , t h e s o l i d l i n e s d e f i n i n g t h e s e a b r e e z e a t LJCLA i n c l u d e winds from w to Ssw.

I n t h e d i f f e r e n t i a t i o n o f s u r f a c e winds and winds i n t h e lowest l e v e l s , topography d e t e r m i n e s t h e t y p i c a l d i r e c t i o n s f o r a g i v e n s t a t i o n . For t h i s r e a s o n , i n t h e s e p a r a t i o n o f s u r f a c e d i r e c t i o n s i n t o l a n d and sea b r e e z e s , l o c a l f a c t o r s h a v e been c o n s i d e r e d and no u n i f o r m set o f c r i t e r i a adopted.

In o r d e r t o d e m o n s t r a t e t h e v a r i q t y o f p a t t e r n s e x p e r i e n c e d , Figures 4 and 5 p r o v i d e a t i m e s e c t i o n f o r 24 c o n s e c u t i v e d a y s a t UCLA. A r e l a t i v e l y s m a l l number o f w i n d a r r o w s a r e p l o t t e d o n t h e s e d i a g r a m s b u t t h e y h a v e b e e n c h o s e n t o r e p r e s e n t t h e g e n e r a l c o n d i t i o n o f f l o w a t t h a t l e v e l and t i m e . Ch most d a y s t h e number o f p i b a l s a v a i l a b l e f o r t h e c o n - s t r u c t i o n o f Figures 4 and 5 w a s comparable t o t h a t shown o n F i g u r e 3 i n w h i c h a l l a v a i l a b l e d a t a have been p l o t t e d .

I f t h e winds i n t h e 8000-10,000 f o o t l e y e l s h a v e a d i r e c t i o n d i f f e r e n t f r o m t h o s e be low t h e d e m a r c a t i o n be tween l o c a l s e a - l a n d b r e e z e s a n u p p e r f l o w c a n b e e a s i l y s e e n , b u t when t h e r e i s a g r a d u a l merging o f t h e t w o , no l i n e o f s e p a r a t i o n c a n b e used . As i n t h e c a s e o f 1 8 August ( F i g u r e 41, t h e t o p o f t h e s e a b r e e z e be tween 120U a n d 1 8 0 0 PWT c a n n o t b e s e p a r a t e d f r o m t h e g e n e r a l c i r c u l a t i o n a l o f t . The s t i p p l i n g i n d i c a t e s s e a b r e e z e i n t h e l o w e s t l a y e r , b u t t h e a b s e n c e o f a f u l l - l i n e boundary on t o p i n d i c a t e s t h e g r a d u a l m e r g i n g o f t h e l o c a l a n d g e n e r a l c i r c u l a t i o n . I n c o n t r a s t 1, 2 a n d 3 September ( F i g u r e 5 ) show d e f i n i t e bounda- r i e s o f t h e s e a b r e e z e . S i m i l a r l y t h e l i n e d e n o t i n g t h e boundary o f t h e l a n d wind h a s b e e n b r o k e n or o m i t t e d when t h e z o n e o f t r a n s i t i o n i s a b s e n t o r i s i n d i s t i n c t .

T h e p a t t e r n s i n F i g u r e s 4 a n d 5

7

d e m o n s t r a t e a number o f f a c t s . I n some cases t h e s e a b r e e z e b e g i n s i n t h e l e v e l j u s t above t h e g r o u n d b e f o r e i t i s d i s - c e r n i b l e a t t h e s u r f a c e . lhis i s presumably t h e r e s u l t o f f r i c t i o n , and h a s been n o t e d i n o t h e r r e g i o n s (3) . I n p r a c t i c a l l y n o c a s e d o e s t h e l a n d b r e e z e b e g i n a l o f t b e f o r e i t i s s e e n a t t h e s u r f a c e . T h i s r e s u l t s f r o m t h e f a c t t h a t a d r a i n a g e mountain-wind b e g i n s somewhat s o o n e r t h a n thle more g e n e r a l l a n d wind and merges i n - d i s t i n g u i s h a b l y w i t h i t . me s t a b i l i t y o f t h e s e c o l d l a y e r s t e n d s t o r e d u c e t h e h e i g h t t h r o u g h which t h e d e l a y i n g e f f e c t of f r i c t i o n i s n o t i c e a b l e .

Also , i n n e a r l y e v e r y c a s e , t h e s e a b r e e z e p e r s i s t s a l o f t above t h e l a n d breeze . N o t a s o f t e n , b u t i n many cases, t h e l a n d wind p e r s i s t s a l o f t f o r a t i m e a f t e r t h e s e a b r e e z e b e g i n s a t t h e s u r f a c e .

The s e a b r e e z e i n n e a r l y a l l c a s e s h a s g r e a t e r s p e e d s t h a n d o e s t h e l a n d wind. This i s d u e i n p a r t t o t h e f a c t t h a t t h e t m p e r a t u r e o f a i r o v e r l a n d d u r i n g t h e day r.tses f a r t h e r above t h e t e m p e r a t u r e o f a i r o v e r s e a t h a n i t f a l l s b e l o w t h e l a t t e r d u r i n g t h e n i g h t . Also, owing to t h e quasi- permanent P a c i f i c a n t i c y c l o n e , t h e g e n e r a l c i r c u l a t i o n i n t h e lower l a y e r s i s from t h e N'8 over ' s o u t h e r n C a l i f o r n i a which r e s u l t s i n a no rma l o n - s h o r e p r e s s u r e g r a d i e n t .

E a s t e r l y winds r e p r e s e n t i n g t h e l a n d b r e e z e o c c u r on e v e r y day except i n u n u s u a l i n s t a n c e s o f v e r y s t r o n g N o r hW winds. (3n s s m e days t h e Land wind p e r s i s t s a l o f t o v e r t h e s e a b r e e z e d u r i n g t h e whole d a y a s i n t h e c a s e s o f 30 Augus t t o 3 S e p t e m b e r .

The z o n e of t r a n s i t i o n be tween s e a - l a n d b r e e z e r e g i m e a n d u p p e r f.low i s u s u a l l y m a r k e d b y a g r a d u a l t u r n i n g o f wind w i t h h e i g h t , b u t n o t i n any o b v i o u s r e g u l a r manner; t h u s no c o n s i s t e n t reg ime o f , a d v e c t i o n can b e descr ibed .

The m e r g i n g o f t h e s e a - l a n d w i n d reg ime w i t h t h e g e n e r a l c i r c u l a t i o n a l o f t has t w o d i s t i n c t i v e p a t t e r n s . The f i r s t , c h a r a c t e r i z e d b y p e r s i s t e n t e a s t e r l y f l o w a b o v e t h e s e a b r e e z e , i s u s u a l l y t h e r e s u l t o f t h e t h e r m a l l o w c e n t e r e d o v e r t h e s o u t h e r n Mojave d e s e r t . B r i n g t h e r e r i o d 1 - 2 S e p t e m b e r , t h e t h e r m a l l o w was s t r o n g a t t h e s u r f a c e and d e f i n i t e l y i n e v i d e n c e a t 5000 f e e t , c o n t r o l l i n g a l l t h e w i n d s a t t h a t l e v e l t h r o u g h ~ u t t h e 5,outhwestern s t a t e s . This l o w was s t r e n g t h - t n e d by a t r o u g h a s s o c i a t e d w i t h a c l o s e d l o w o v e r s o u t h e r n I d a h o a t 20 ,000 f e e t . 'fie e a s t e r l i e s a t UCLA shown on t h e t i m e s e c t i o n b e t w e e n 2 0 0 0 a n d 6000 f e e t o n t h e s e d a t e s f i t t e d i n t o t h e p a t t e r n o f

winds a t o t h e r s t a t i o n s i n t h e a r e a . ne sea b r e e z e was e v i d e n t o n l y a t s t a t i o n s be tween t h e c o a s t and t h e coast r a n g e o f m o u n t a i n s . I t w i l l b e n o t e d t h a t a b o v e 6000 f e e t t h e w i n d s were w e s t e r l y , re- p r e s e n t i n g t h e r e p l a c e m e n t o f t h e l o w p r e s s u r e i n t h e lower l a y e r s by a h igh a l o f t a s t h e l o w c e n t e r s l o p e d upward t o t h e north. 01 t h e s e days t h e l a n d b r e e z e merged w i t h t h e e a s t e r l y w i n d s c a u s e d b y t h e thermal l o w .

n e s e c o n d p a t t e r n i s e x e m p l i f i e d b y 5 - 6 S e p t e m b e r ( s e e F i g u r e 1 3 ) a t w h i c h t i m e a s t r o n g thermal. low e x t e n d e d f a r u p t h e i n l a n d v a l l e y s o f C a l i f o r n i a g i v i n g r i s e t o w e s t e r l i e s o r lW' w i n d s a t 3 0 0 0 - 5000 f e e t a t UCLA. I n t h i s c a s e t h e s e a b r e e z e m e r g e d w i t h t h e u p p e r f low. A t 10,000 f e e t , however, a h i g h was c e n t e r e d o v e r t h e G r e a t B a s i n , Wyoming and Idaho, and t h e e a s t e r l y w i n d s f rom 6000-10,00V f e e t a r e d i f f e r e n t i a t e d f r o m t h e w i n d s between 3000 and 6000 f e e t .

Thus i t a p p e a r s t h a t t h e r e a r e t h r e e l a y e r s each o f d i s t i n c t wind p a t t e r n , below t h e g e n e r a l u p p e r f low. The l o w e s t a n d most l o c a l i s t h e v a l l e y - m o u n t a i n w i n d r e g i m e , c o n t r o l l e d b y t h e d e t a i l s o f topography. ne n e x t i s t h e s e a - l a n d b r e e z e p a t t e r n , a l s o c h a r a c t e r i z e d b y a d i u r n a l c y c l e , a c t i v a t e d by t h e d i f f e r e n t i a l h e a t - i n g o f a i r o v e r l a n d and sea. T h i s regime i s c o n f i n e d t o t h e c o a s t a l p l a i n a n d t h e o c e a n a r e a i m m e d i a t e l y a d j a c e n t t o t h e c o a s t . J u s t above t h e s e a - l a n d b r e e z e i s t h e t h i r d wind p a t t e r n , c o n t r o l l e d by t h e t h e r m a l l o w , a n d n o t c o n f i n e d t o t h e c o a s t a l p l a i n . I t a f f e c t s t h e f low i n l a n d a s f a r a s t h e c e n t e r o f t h e s o u t h w e s t e r n d e s e r t . On p a r t i c u l a r days t h e thernial low i s d e f i n i t e l y i n e v i d e n c e a t 5000 f e e t n o t o n l y d u r i n g t h e dayt ime b u t f o r a p o r t i o n of t h e n i g h t . I t h a s a d i u r n a l c y c l e o f changing i n t e n s i t y , b u t a t t imes e x i s t s a t 5000 f e e t d u r i n g a p e r i o d o f more than o n e day. The d i u r n a l wind regime produced h a s b e e n c a l l e d a c o n t i n e n t - o c e a n wind (2) . A t s u c h t i m e s d u r i n g which a l o w p r e s s u r e a r e a o v e r t h e l a n d p e r s i s t s , t h e o n - s h o r e f low i n t h e l a y e r j u s t above t h e s e a b r e e z e approaches t h e c h a r a c t e r of a t r u e monsoon.

me g e n e r a l c i r c u l a t i o n a l o f t which i s l i t t l e a f f e c t e d by t h e l o c a l h e a t i n g o f t h e c o a s t l i n e o r t h e d e s e r t t h e r m a l l o w p r e v a i l s above t h e m o n s o o n a l . w i n d s .

n e l e i s o r d i n a r i l y a g r a d u a l merging o f e a c h o f t h e s e p a t t e r n s i n t o t h e o n e above i t , b u t o n c e r t a i n d a y s t h e l i m i t s o f e a c h l a y e r can b e d e f i n i t e l y s e e n .

AVERAGE DIURNAL WIND TIME-SECTION AT UCLA

The a v e r a g e d i u r n a l w ind r eg ime i n h e i g h t a n d t i m e h a s b e e n r e p r e s e n t e d i n F i g u r e 15 f o r t h r e e p e r i o d s , r o u g h l y re- p r e s e n t i n g summer, f a l l and w i n t e r seasons . T h e s e d i a g r a m s h a v e b e e n c o n s t r u c t e d t o show t h e p r e d o m i n a n t wind d i r e c t i o n a n d f o r c e f o r each 500-f t l e v e l and f o r a s many i n d i v i d u a l h o u r s d u r i n g t h e day a s t h e d a t a allowed.

? h e 45' sec tor c o n t a i n i n g t h e l a r g e s t number o f c a s e s de t e rmined t h e predominant d i r e c t i o n which i s r e p r e s e n t e d by t h e arrow. Each wind arrow i s l a b e l e d t o show t h e t o t a l number a f o b s e r v a t i o n s a t t h a t t ime and l e v e l a n d t h e number o f o b s e r v a t i o n s i n w h i c h t h e w i n d w a s from t h e d i r e c t i o n shown by the arrow. M e n a n o t h e r d i r e c t i o n a l s o c o n t a i n e d a l a r g e number o f o b s e r - v a t i o n s , a s e c o n d a r y d o t t e d a r row i s shown and l a b e l e d w i t h t h e number o f cases. The wind f o r c e i s i n d i c a t e d by b a r b s i n t h e B e a u f o r t s c a l e a n d i s a r o u g h a v e r a g e d e t e r m i n e d b y v i s u a l i n s p e c t i o n o f t h e t a l l y .

T h i s m e t h o d o f r e p r e s e n t i n g t h e dominant wind d i r e c t i o n d o e s n o t g i v e t h e completc: d i s t r i b u t i o n a s would a wind rose b u t h a s t h e a d v a n t a g e o f f a c i l i t a t i n g a v i s u a l summary o f t h e d a t a . The comple te wind d i r e c t i o n f r e q u e n c y r o s e s a t m o s t o f t h e same l e v e l s and t i m e s a r e p r e s e n t e d i n F i g u r e s 7 t o 9. The roses w i l l a l l o w t h e r e a d e r t o check f o r h i m s e l f t h e predominant d i r e c t i o n s s u m m a r i z e d i n t h e a v e r a g e d i u r n a l t i m e - s e c t i o n s . A l l d a t a u s e d i n t h e s e a v e r a g e s w e r e o b t a i n e d a t t h e AAF R a t h e r S t a t i o n , UClA.

The a v e r a g e time s e c t i o n s h a v e b e e n a n a l y z t z d i n t h e s a m e m a n n e r d e s c r i b e d p r e v i o u s l y . On t h e b a s i s o f t h e a n a l y s i s compar isons be tween s e a s o n s may be drawn.

The a v e r a g e s f o r a l l t h r e e s e a s o n s h a v e t h e f o l l o w i n g c h a r a c t e r i - s t i c s i n common. In t h e lowes t 2000 f e e t t h e r e i s a c y c l i c c h a n g e f rom SW i n t h e a f t e r n o o n t o e a s t e r l y i n t h e e v e n i n g a n d e a r l y m o r n i n g . T h e SW s e a b r e e z e h a d t h e l o n g e s t d u r a t i o n i n t h e summer a n d t h e s h o r t e s t i n t h e w i n t e r .

The t o t a l h e i g h t o f t h e s e a b r e e z e a p p a r e n t l y e x c e e d s 5 0 0 0 f e e t . i n summer, appears t o be ' abou t 5000 f ee t i n t h e f a l l and 3500 f e e t i n t h e w i n t e r , The easter- l i e s c c n s t i t u t e a g r e a t e r d u r a t i o n o f t ime i n t h e low'er l a y e r s t h a n d o e s t h e s e a b r e e z e and a p p a r e n t l y e x t e n d t o g r e a t e r h e i g h t than t h e s e a breeze . ' h e e a s t e r l i e s

a r e p r e d o m i n a n t i n t h e l o w e s t l a y e r s t h r o u g h o u t t h e n i g h t a n d e a r l y morn ing , b u t a l o f t a r e p r e s e n t d u r i n g t h e morning h o u r s , b e i n g r e p l a c e d by a d i f f e r e n t u p p e r flow between midnight and 0300.

The f a c t t h a t a l l t h r e e s e a s o n s show t h e r e l a t i v e l y s m a l l d e p t h o f t h e e a s t wind be tween 0000 and 0 3 0 0 P W i n d i c a t e s t h a t t h i s f e a t u r e i s p r o b a b l y c h a r a c t e r i s t i c of t h e s e a - l a n d b r e e z e s t r u c t u r e i n t h e a rea . S i m i l a r l y , t h e g r e a t depth o f e a s t e r - l i e s a t 0900 and 1100 PWT d u r i n g a l l t h r e e s e a s o n s s u g g e s t s t h a t t h i s i s a l s o charac- t e r i s t i c e

Inasmuch a s t h e a v e r a g e h e i g h t s f t h e b a s e o f t h e t e m p e r a t u r e , i n v e r s i o n a t IJCLA was a b o u t 1 5 0 0 f e e t , t h e a v e r a g e t ime- s e c t i o n s c o r r o b o r a t e t h e f i n d i n g s o f t h e s t r a t u s i n v e s t i g a t i o n (1) t h a t t h e h e i g h t o f t h e d i u r n a l w i n d f l u c t u a t i o n i s n o t l i m i t e d by t h e i n v e r s i o n . I t h a s b e e n s u g g e s t e d (2) t h a t "an i n v e r s i o n of temper- a t u r e and a d e c r e a s e o f r e l a t i v e h u m i d i t y c h a r a c t e r i z e t h e v e r t i c a l e x t e n t o f t h e l a n d b r e e z e . " I n t h e Los Ange les B a s i n , t h e d i u r n a l wind changes a t t r i b u t e d t o t h e s e a - l a n d b r e e z e r eg ime d e f i n i t e l y o c c u r c o n s i d e r a b l y above t h e prominent s u b s i d e n c e i n v e r s i o n .

T h e maximum v e l o c i t i e s o f t h e s e a b r e e z e o c c u r r e d a t 1000 t o 1500 f e e t n i s l a t UCLA, t h e e l e v a t i o n o f w h i c h i s 500 f e e t . .

S i m i l a r t o t h e t i m e s e c t i o n s f o r i - n d i v i d u a l - d a y s , t h e a v e r a g e s show t h a t t h e l a n d b r e e z e i s s t i l l b l o w i n g a l o f t a t t h e time t h e s e a b r e e z e b e g i n s i n t h e lower l a y e r s . The p e r s i s t e n c e of t h e s e a b r e e z e a b o v e t h e i n i t i a l l a n d wind i s , however, much less d i s t i n c t .

I t w i l l b e n o t e d t h a t i n t h e a v e r a g e p i c t u r e t h e s e a b r e e z e v e e r s s l i g h t l y w i t h h e i g h t w h i l e t h e l a n d b r e e z e h a s a tendency t o back w i t h h e i g h t . As p r e v i o u s l y mention- ed i n s p e c t i o n o f i n d i v i d u a l d a y s d i d n o t r e v e a l any c o n s i s t e n t p a t t e r n of t u r n i n g w i t h h e i g h t . The t u r n i n g c a n n o t b e e x - p l a i n e d by a d v e c t i o n o f t h e t r o u g h of t h e t e m p e r a t u r e i n v e r s i o n b e c a u s e i t o c c u r s i n J a n u a r y when t h e i n v e r s i o n i s a b s e n t a s w e l l a s i n summer when i t i s p r e s e n t . T h e o b s e r v e d t u r n i n g i s s a t i s f a c t o r i l y e x p l a i n e d by t h e c o n s i d e r a t i o n o f t h e a d d i t i o n o f v e c t o r s r e p r e s e n t i n g t h e d e c r e a s e d e f f e c t o f t h e l a n d - s e a b r e e z e r e g i m e w i t h h e i g h t a n d t h e m e r g i n g w i t h

9

t:he uppe r f low a s e x p l a i n e d p r e v i o u s l y i n t h e d i s c u s s i o n o f t h e wind t i m e - s e c t i o n f o r 1 S e p t e m b e r 1944.

, An a t t e m p t was made t o r e l a t i : t h e t u r n i n g of wind w i t h h e i g h t t o t empera tu re a d v e c t i o n making u s e o f wind and raob d a t a p l o t t e d on c o n s t a n t - l e v e l c h a r t s fo r each 1 0 0 0 - f o o t l e v e l . E v e n w i t h t h e . c l o s e

ne twork o f r a d i o s o n d e s i n t h e IDS h g e l e s : B a s h d u r i n g t h e summer o f 1944, s a t i s - f a c t o r y a n a l y s e s c o u l d n o t be made because Ithe t e m p e r a t u r e and p r e s s u r e d i f f e r e n c e s between s t a t i o n s were no l a r g e r t h a n t h e p r o b a b l e e r r o r i n t h e v a l u e s measured by t h e r a d i o s o n d e .

A t t h e t i m e t h e s e a b r e e z e b e g i n s i n t h e l o w e s t l e v e l s t h e ea s t e r l i e s a r e s t i l l b lowing a l o f t and assume t h e n a t u r e o f a c o u n t e r c u r r e n t t o t h e l o w e r winds . The same t h i n g happens t o a l e s s e r deg ree when t h e l a n d w i n d b e g i n s n e a r t h e s u r f a c e , 'Ihe i n c r e a s e i n dep th o f t h e s e a b r e e z e a t t h e e x p e n s e o f t h e c o u n t e r c u r r e n t a l o f t f i t s t h e t h e o r y o f t h e s e a - l a n d r e g i m e m o s t g e n e r a l l y a c c e p t e d ( I ) , ( 3 ) . The c o u n t e r c u r r e n t a l o f t l a s t s l o n g e r a t Ba tav ia (3) t h a n i n t h e Los Ange les Bas in , b u t a t Fe l ixs tow, England t h e ave rage depth o f t h e s e a b r e e z e i s 1 5 0 0 f e e t and t h e r e i s no i n d i c a t i o n o f a c o u n t e r c u r r e n t , a t l e a s t up t o 5500 f e e t (4). The Ba tav ia s tudy showed t h a t t h e e f f e c t o f t h e c o u n t e r c u r r e n t r e a c h e d a s h i g h a s 1 2 , 000 f e e t , w h i l e a t Los A n g e l e s t h e e a s t e r l i e s u s u a l l y merge i n t o an u p p e r f l o w a t l e v e l s n o t exceed- i n g 6000 feet. However, i f t h e p r e v a i l i n g wind a l o f t w e r e weak a s i n t h e c a s e a t Ba tav ia , the land-sea winds prpbab ly would be shown a t l e v e l s h i g h e r t han 6000 f e e t . A s p r e f i o u s l y e x p l a i n e d , t h e t u r n i n g o f wind w i t h h e i g h t i n d i c a t e s t h a t some coni- p o n e n t o f t h e l a n d - s e a r e g i m e i s o f t e n d i s c e r n i b l e a b o v e t h e l i n e s on t h e t i m e s e c t i o n s d e l i n e a t i n g t h e e a s t e r l i e s and t h e s o u t h w e s t e r l y winds.

Having now o b t a i n e d some knowledge o f t h e a v e r a g e d i u r n a l w ind c h a n g e s i n t h e Los h g e l e s a r e a , a d e t a i l e d e x a m i n a t i o n o f the changes on one p a r t i c u l a r day p roves i n t e r e s t i n g .

AREAL PATTERN ON AN INDIVTDUAL DAY

To make a three-d imens iona l p i c t u r e of t h e s e a b r e e z e on an i n d i v i d u a l day , t h e coope ra t ion of c e r t a i n AAF weather s t a t i o n s was e n l i s t e d . On 5-6 September 1944, s i x s t a t i o n s i n t h e Los Ange les a r e a o b s e r v e d

10

slow a s c e n t p i b a l s a t t i m e i n t e r v a l s of 1 1 / 2 h o u r s f o r a 24 h o u r p e r i o d . Thc time s e c t i o n s of wind f o r a l l s t a t i o n s a re shown i n F i g u r e s 10 and 11.

The day chosen f o r t h e o b s e r v a t i o n s was a t t h e end of a p e r i o d of s t r a t u s and t h e b e g i n n i n g o f a foehn c o n d i t i o n c a u s e d by t h e deve lopment of a h i g h - p r e s s u r e c e n t e r ove r the G r e a t Basin,

The t i m e - h e i g h t p a t t e r n o f t h e sea and l a n d b r e e z e regime a t v a r i o u s s t a t i o n s i s g i v e n b y t h e s o l i d , o r d a s h e d l i n e s i n F i g u r e s 10 and 11. S i n c e t h e flow between 2000 and 5000 f e e t was g e n e r a l l y westerly t h r o u g h o u t t h e 24 h o u r s , t h e p a t t e r n of t h e e a s t e r l y land wind i n t h e lowes t l a y e r s is w e l l d e l i n e a t e d .

A t 1500 m, 5 September , t h e the rma l l o w o v e r t h e Mojave Desert w a s w e l l marked a t 5000 f e e t a n d s t i l l p r e s e n t a t t h a t l e v e l a t 2100 m, a s can be seen on F igu re 13. A t 1 0 , 0 0 0 f e e t a t t h i s t i m e w i n d s o v e r t h e a r e a were c o n t r o l l e d by t h e h i g h c e n t e r i n Idaho . T h e r e were no f r o n t s i n t h e w e s t e r n U n i t e d S t a t e s d u r i n g t h e period.

I n s p e c t i o n of t he U U A t ime-sec t ion of t h i s d a t e ( F i g u r e 10) s h o w s t h a t t h e w e s t e r l i e s i n t h e l e v e l 2 0 0 0 - 5 0 0 0 f e e t p e r s i s t e d f rom 1500 on t h e 5 t h t o noon of t h e 6 t h . The c o a s t a l s e a b r e e z e i n t h e l o w e r l a y e r s a p p a r e n t l y merged i n t o t h e w e s t e r l i e s c o n t r o l l e d by t h e the rma l l o w . C i r c u l a t i o n a r o u n d t h e t h e r m a l l o w c a n b e s e e n a t 5 0 0 0 f e e t a t 0 3 0 0 PWT on 6 Sep tember ( F i g u r e 13). By 0900, however, t h e winds a t 5000 feet o v e r most C a l i f o r n i s t a t i o n s were e a s t e r l y , now c o n t r o l l e d b the Grea t Bas in h igh .

To p r o v i d e a n e a s i e r s y n t h e s i s o t h e g e o g r a p h i c p i c t u r e o f t h e d e v e l o p + ment of t h e loca l -wind p a t t e r n , t h e c r o s s s e c t i o n o f F i g u r e 1 2 i s p r e s e n t e d . I r e p r e s e n t s a p r o f i l e from t h e coas t i n l a n d e a c h s t a t i o n shown a p p r o x i m a t e l y a t p e r p e n d i c u l a r d i s t a n c e f rom t h e c o a s t . Va Nuys (DVN) l i e s i n t h e San Fernando V a l l e which e x p e r i e n c e s a s e a b r e e z e f l o w i n g i f r o m t h e p a s s e s t o t h e s o u t h e a s t a s e x p l a ined i n t h e d i s c u s s i o n of F igu re 1. Ihe d i s t a n c e a l o n g t h e t r a j e c t o r y of t h e sea b r e e z e was used t o p l a c e DVN and IW on t h e p r o f i l e .

A t 1800 PWT on t h e 5 t h a l l s t a t i o n s shown on t h e p r o f i l e were e x p e r i e n c i n g w e s t e r l y s e a b r e e z e , The uppe r p o r t i o n o F i g u r e 1 2 s h o w s t h e d e v e l o p m e n t o f t h

1 l a n d wind from 1900 t o 0100 . At 1900 t h e w i n d shows o n l y a s a s h a l l o w l a y e r o f eas te r ly winds n e a r t h e s u r f a c e a t UCLA, WN and CUA. At 2100 e a s t e r l i e s occur from t h e s u r F a c e up t o 1500 f e e t a t U U A , DVN and IJUA, bu t westerlies a r e s t i l l occur r ing a t L4 and a t Dol. The development eastward o f t h e land wind a t t h e s u r f a c e a s shown by t h e p r o f i l e s was checked w i t h t h e s u r - f a c e w i n d s a t s t a t i o n s l a y i n g n e a r t h e c ros s - sec t ion l i n e .

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S

g f e

?he lower se t of p r o f i l e s i n F igu re 12 shows a u n i f o r m l y d e v e l o p i n g l a y e r o f e a s t e r l y wind r ep resen ted by the a rea below t h e p r o f i l e l i n e s o f 0 3 0 0 and 0 6 0 0 . I t w i l l be noted t h a t t he l a n d wind began n e a r t h e coas t and worked i n l a n d , i n c r e a s i n g i n d e p t h f a s t e s t o v e r t h e i n l a n d s t a t i o n s . The f i r s t p i b a l s h o w i n g a n y l a n d wind above L4 was 0300 a s can be seen on F i g u r e 10. This l a t e beg inn ing of t h e e a s t winds a t LA i s t y p i c a l o f t h e a v e r a g e s u r f a c e - wind regimes shown i n F igu re 1.

A t 0900 t h e l and wind i s developed a t a l l s t a . t i ons but LA shows a s e a b reeze up t o l lQO f e e t a n d a l a y e r o f e a s t e r l i e s b e t w e e n 1100 a n d 2 7 0 0 f e e t . By 1300 w e s t e r l y s e a wind o c c u r s a t a l l s t a t i o n s except the most i n l a n d , TUT. .4 t h i n l a y e r o f east: winds can b e s e e n a t t h i s hour a t

LA and UCZA a t 1500 f e e t , and a t 3000 f e e t a t DVN, wh i l e a c o n s i d e r a b l e t h i c k n e s s of e a s t e r l i e s i s s t i l l p re sen t a t (2000 t o 4200 f e e t ) and a t DO1 (3500 t o above 5000 f e e t ) . The f a c t t h a t t h e sea b r e e z e a t 1300 PWT i s t h i c k e r a t DVN t h a n a t IXJA i s p r o b a b l y e x p l a i n e d by t h e f a c t t h a t t h e two s t a t i o n s a r e n o t a s c l o s e t o g e t h e r g e o g r a p h i c a l l y a s t h e p r o f i l e i n d i c a t e s .

REFERENCES

f i e Ca l i f o r n i a S t r a t u s I n v e s t i g a t i o n o f 1 9 4 4 b y N e i b u r g e r , B e e r , a n d Leopold ; p u b l i s h e d b y U . S . Dept. o f Commerce, Weather Bureau, A p r i l 1945 f o r t h e J o i n t Me teo ro log ica l @nunittee.

Local Winds; Weather D iv i s ion Report # 9 8 2 , Hq Army A i r F o r c e s , F e b r u a r y 1945 (Res t r i c t ed )

Tropical Land and Sea Breezes; ( B r i t i s h ) Naval Meteoro logica l Branch, hlemo 126, 1944 (Res t r i c t ed ) .

Sea Breezes and Land Breezes; M e t e o r o l o g i c a l O f f i c e , ( B r i t i s h ) Air M i n i s t r y , Synop t i c D i v i s i o n Techn ica l Memo #SS, 1943. (Reprinted U.S. Navy, NAVAER 50-IR-$2, August 1944)

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