TABLE OF CONTENTS
Page
Summary
1
Introduction
1
S u r f a c e Winds
2
D i u r n a l Wind-Regime A l o f t a t Uc3A
6
9
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
10
Ref e r e n c e s
11
LIST OF FIGURES
Figure
Number
Title
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 A n g e l e s B a s i n , August 1944
2
P r e v a i l i n g - W i n d Flow a t H o u r o f Maximum
Sea-Breeze Development (Late A f t e r n o o n ) ,
o v e r Los A n g e l e s B a s i n , August 1944
Sample Wind T i m e - S e c t i o n , U M ,
1 September
1944
4
Time S e c t i o n o f w i n d s above KIA, 18-29 Augu s t 1944
5
Time S e c t i o n o f Winds above U a , 30August10 September 1944.
6
Predominant D a i l y Winds a t U U A
7
W i n d - D i r e c t i o n Frequency Roses-a.
14 Aug. 17 Sep 1944 0300-1100 PWT
n
1300-1700 PWT
b.
C.
8
Wind-Direction Frequency R o s e s - U a
a.
18 Sep-20 Nov. 1944 0300-0900 pwf
n
1100-1500 m
b.
C.
9
1900-2400 PWT
n
1700-2400 PWT
n
Wing-Di r e c t i q n F r e q u e n c y R o s e s - m
0500-0900 PWT
a.
8-31 Jan. 1945
b.
n
1100-1500 PRT
C.
n
1700-,1900 PWT
10
Wind T i m e - S e c t i o n s 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 .
11
Wind T i m e - S e c t i o n s a t V a r i o u s S t a t i o n s 5-6
September 1944 VanNuys, Cal. Tech, 9 n t a r i o .
12
P r o f i l e s of Land and S e a 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 S e p t e m b e r
1944
13
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 o f s l o w - a s c e n t p i l o t balloon observations t h e three-dimensional
s t r u c t u r e i n t i m e of t h e s e a and 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 mately perpendicular to the l o c a l coast
l i n e b u t f o l l o w s u p t h e t h a l w e g of i n l a n d
valleys.
The s e a b r e e z e t e n d s t o m e r g e 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 winds, and t h e
The s e a l a n d b r e e z e w i t h m o u n t a i n winds.
l a n d b r e e z e r e g i m e is 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 m o u n t a i n
range, b u t flows through the m o s t w e s t e r l y
p a s s e s 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 passes.
At h i g h e r l e v e l s t h e r e i s a t e n d e n c y
f o r t h e s e a - l a n d breeze p a t t e r n t o m e r g e
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
s o u t h w q s t e r n desert. When t h e t h e r m 1 l o w
p e r s i s t s both n i g h t and day f o r s h o r t
p e r i o d s of 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 a p p r o a c h e s 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 w i n d
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 o c e a n c o n t i n e n t wind b y 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 o v e r t h e G r e a t Basin, e a s t e r l y f l o w
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 m e r g e
w i t h t h e land wind and c o n f i n e t h e w e s t e r l y
s e a breeze t o a small depth and s h o r t
duration.
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 appearance progressively inland.
It
d e e p e n s 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 e a c h e s a g r e a t e r d e p t h
i n summer t h a n i n . w i n t e r .
T h e combined l a n d - m o u n t a i n w i n d
a p p e a r s 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 i m e s i t
appears l a s t a t the coastal s t a t i o n s .
It
deepens f a s t e r i n l a n d than a t the 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
seasons:
summer, f a l l and 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 southern C a l i f o r n i a duri n g t h e summer of 1944 (1) e m p h a s i z e d t h e
importance o f t h e s e a - l a n d b r e e z e 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 weather.
T h e 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 . D u r i n g 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 o f w i n d 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 obs e r v a t i o n s i n t h e l a t e f a l l and winter.
These d a t a c o n s t i t u t e t h e b a s i s for t h e
p r e s e n t rctport.
I t is concerned primarily
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 o f , t h e s e a b r e e z e o n
p a r t i c u l a r d a y s 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 W e a t h e r 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 A n g e l e s ( V U ) by means
of s low a s ce n t p i1ot b a 11oons wh i ch a 11owe d o b s e r v a t i o n s t o b e t a k e n a t v e r t i c a l in-5
t e r v a l s o f a b o u t IS0 f e e t . The p e r i o d s o f
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 circums t a n c e s a l l o w e d , which c o n s t i t u t e d a p p r o x i 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 .
In addition,
a n a l y s e s w e r e 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 r o u n d i n g 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 R a w i n d a t a
t a k e n a t Mines F i e l d (XA) w h i c h i s l o c a t e d
n i n e m i l e s SSE o f UCLA.
-
-
The d e s c r i p t i o n o f t h e w i n d 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 i s a
'discussion of a l l factors related to 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 i s o n e of t h e p r e 8
1
liminary s t e p s toward t h e complete understanding.
In t h i s r e p o r t t h e s e a - l a n d wind
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 t h e e f f e c t
of t h e l a n d - s e a 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 c h a n g e i n wind d i r e c t i o n i n t h e Los
Angeles B a s i n is found b o t h below and above
the temperature i n v e r s i o n which i s a
c h a r a c t e r i s t i c o f t h e summer i n t h i s a r e a .
Below t h e i n v e r s i o n t h e m a r i n e 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 .
The v a l l e y - m o u n t a i n wind r e g i m e i s
similarly defined a s a diurnal oscillation
o f d i r e c t i o n a t any l e v e l due t o t e m p e r a t u r e
d i f f e r e n c e s between t h e a i r o v e r t h e v a l l e y
The%upa n d a i r o v e r t h e lower p l a i n .
v a l l e y wind i s termed s i m p l y t h e v a l l e y
wind w h i l e t h e d o w n - v a l l e y wind i s c a l l e d
t h e mountainwind.
I n g e n e r a l , s l o p e or
d r a i n a g e winds i n d u c e d b y t e m p e r a t u r e 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 s u r f a c e of t h e mountain s l o p e s a r e c o n s i d e r e d
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 w h i c h
c o n s i s t o f a m e r g e r of t h e s e a and v a l l e y
b r e e z e s or of t h e l a n d and mountain b r e e z e s .
S u r f a c e winds o f t h i s t y p e , as 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 " a n d "land-mountain" winds, r e s p e c t lively.
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 n e a r
t h e c o a s t , where t h e l a n d a n d s e a b r e e z e s
are the primary e f f e c t s , the term "sea
b r e e z e " when a p p l i e d t o w i n d s 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 any
e f f e c t s o f t h e v a l l e y wihd.
Similarly the
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
upper a i r w i l l i n c l u d e mountain winds.
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 report.
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. S p a c e l i m i t a t i o n r e q u i r e d t h e u s e
of 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 .
These are l i s t e d ,
together with s t a t i o n e l e v a t i o n s , i n Table
1 below.
TABLE I
CALL LETTERS AND STATION ELEVATIONS
call
Station
Oceanside
E l Tor0 (Marine Corps
Air S t a t i o n )
Orange County Army Air
Field
Long Beach Army Air
Fie I d
San Pedro (Naval Air
Station)
Lomita F l i g h t S t r i p
US Angeles A i r p o i t
(Mines F i e l d )
U n i v e r s i t y of C a l i f o r n i a
a t Los Angeles
G l e n d d e (Grand C e n t r a l
Terminal)
Van M y s ( M e t r o p o l i t a n
Airport)
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
Field
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)
Letters
Elevation
(Ft. m s l . )
oc
10
332
Dsw
52
HB
40
Ncx
10
106
96
505
46 2
DGX
9
DVN
7 97
1190
82
758
9 20
1098
1528
2592
420
NCB
so5
NSA
906
7 25
5 12
SURFACE WINDS
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 o f 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 A u g u s t 1944.
Although 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
a v e r a g e s , i t i s b e l i e v e d t h a t t h i s month i s
2
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
teletype reports.
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 d u r i n g 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 e a c h s t a t i o n i s
s u m m a r i z e d i n F i g u r e 1 on w h i c h a r e i n d i c a t e d t h e average t i m e o f beginning 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
h o u r s n o t i n c l u d e d i n t h e s t a t i o n m o d e l may
b e 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
regime 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 r o w s r e p r e s e n t
t h e a v e r a g e maximum d a i l y s p e e d s .
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 s e d
t o d e c i d e when a wind i s p r e v a i l i n g may b e
d e s i r a b l e . A c e r t a i n amount o f 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 w a s r e quired.
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 r o m any o t h e r 45' s e c t o r (or c a l m s ) 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 o f
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 hour.
This defin i t i o n permitted t h e analysis of the night
b r e e z e s w h i c h u s u a l l y s h o w e d r a t h e r low
f requeiicies b u t w e r e 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
other iirections.
A l l calms i n d i c a t e d a s
"prevailing" i n Figure 1 represented over
50% of t h e o b s e r v a t i o n s f o r t h e h o u r s given.
The d a i l y s e a b r e e z e w a s a p p a r e n t a t
a11 s t a t i o n s i n t h e basin.
I n addition,
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 w a s obs 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
mount,iin and 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 a n d
breeze circulation, since both tend 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 surface
winds a r e i n f l u e n c e d markedly by the
topography, e v e n t h e lowest h i l l s p l a y i n g
a n o t i : e a b l e p a r t i n t h e summer c i r c u l a t i o n
H i l l s l o w e r t h a n 1000 f e e t c o u l d - n o t b e
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
For a more
mentioned i n t h e d i s c u s s i o n s .
d e t a i l e d map o f t h e t o p o g r a p h y of t h e Los
Angelcs Basin t h e reader is r e f e r r e d t o
F i g u r c : 2, t a k e n f r o m t h e r e p o r t of C a l i f o k n i s . S t r a t u s I n v e s t i g a t i o n o f 1944 (1) *
' h e d a y t i m e wind regime 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 of 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 .
These should r e p r e s e n t t h e flow n e a r t h e
t i m e of maximum s e a b r e e z e , w h i c h i s a l s o
It
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 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 o n s h o r e a p p r o x i m a t e l y
perpendicular t o the l o c a l c o a s t l i n e , but
once .Inland is g u i d e d up the main v a l l e y s
toward the p a s s e s .
The f l o w s p l i t s i n t o
t w o miin s t r e a m s , a s can be c l e a r l y s e e n
on F i g u r e 2.- One s t r e a m f l o w s n o r t h e a s t w a r d
i n t o t h e San F e r n a n d o V a l l e y where Burbank
(BU) a n d Van N u y s 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-
w a r d S a n G o r g o n i o P a s s i n w h i c h Beaumont
(TUT) i s l o c a t e d .
The s e a - v a l l e y w i n d
r e g i m e 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 G o r g o n i o P a s s and 80 m i l e s i n l a n d f r q m 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,
8 0 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 t h e d i u r n a l s h i f t s of t h e
land-sea b r e e z e 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 c h a n g e from p r e v a i l i n g Nw
w i n d s a t S a n 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 a b o u t 80 m i l e s NW o f NCB) t o
WNW w i n d s a t NQB and t o WSW w i n d s a t %A.
lhis a p p e a 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 n o r t h e r n m o s 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
mountains a t Cahuenga P a s s a b o u t 5 m i l e s
w e s t o f t h e Los A n g e l e s R i v e r .
This has
been v e r i f i e d by " 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 very small o r zero 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 w e r e made b u t some
b a l l o o n s w e r e 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 C a h u e n g a 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 , c o m b i n e d
with the n e g l i g i b l e f r e e l i f t , succeeded
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 b e l o w 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
are present 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) a n d s e a w a r d a s
f a r a s San Clemente I s l a n d . These n i g h t
winds a r e , however, weaker t h a n t h e s e a
breeze 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
than 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 b r e e z e and the e f f e c t o f
v a l l e y w i n d s . - A t some s t a t i o n s a w e s t e r l y
w i n d b e g i n s two or t h r e e h o u r s a f t e r sunrise (about 0 6 2 0 i n August) but 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 from t h a t
of t h e m a x i m u m sea b r e e z e . 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 m o r e
general sea breeze..
3
E v i d e n c e of t h e v a l l e y w i n d m e r g i n g
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 .
Rapid 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
breeze t o s t a r t prior t o the sea breeze
i n these cases.
s t a t i o n s near the coast.
Under s u c h cond i t i o n s n o t i c e a b l e c h a n g e s i n b o t h tempera t u r e and m o i s t u r e occur simultaneously
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 within about
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
inaudible 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 .
Analysis of t h e d i u r n a l changes 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 w h i c h may be app l i e d t o many o t h e r s t a t i o n s . T h e s e a v:tlley b r e e z e b e g i n s 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 b y 1 4 3 0 .
T ? i s change of 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
b a l a n c e d flow. D u r i n g t h e p r o g r e s s o f 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 prodilce v e e r i n g of w i n d a t c o a s t a l s t a t i o n s .
The WSW w i n d a t t h e t i m e o f o n s e t may b e
r e g a r d e d , however, a s t h e v e c t o r sum o f 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 b r e e z e blowing i n t o t h e v a l l e y e a s t
01' S a n t a Ana which c a n be s e e n i n F i g u r e 2.
The s e a b r e e z e e f f e c t i n c r e a s e s a s t h e day
p r o g r e s s e s , 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'set.
In g e n e r a l , t h e s p e e d 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 .
Since a true sea
breeze should diminish i n speed f a r t h e r inhind i t i s a g a i n a p p a r e n t t h a t a merging o f
the sea breeze i n t o the v a l l e y wind t a k e s
place. Noticable i n c r e a s e s i n speed a t a
f t w s t a t i o n s ( e . g . , IX)I, IW,RQ a r e prob: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
elcf e c t s
(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 w i n d a t N e w h a l l
0 a t 1100 may b e 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 l o w i n g
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 o v e r
N e w h a l l P a s s from t h e San F e r n a n d o V a l l e y
( s e e F i g u r e 1).
I t is interesting t o note
t h a t t h e r e i s p r a c t i c a l l y no evidence 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
Clara Valley.
T h i s w o u l d 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
followed i n passing up t h e San Fernando
Valley.
The r e a s o n f o r t h e p r e d o m i n a n c e
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 e x p a n s e of low e l e v a t i o n i n t h e San
Fernando V a l l e y , w i t h r e l a t i v e l y s m a 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 i g h e r mountain ranges.
.
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
OF the sea-valley breeze a t inland s t a t i o n s
s u c h a s N e w h a l l (NH) and March F i e l d (RVI
o c c u r s o n l y one or t w o h o u r s l a t e r t h a n a t
t h e 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 w h i c h 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 reached 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 , not a c h a r a c t e r i s t i c of
the sea-valley breeze i n t h i s report.
Fi-esh m a r i n e a i r w i l l , of c o u r s e , 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 c h a n g e of wind d i r e c t i o n may o c c u r
s e v e r a l h o u r s b e f o r e t h e a r r i v a l of t h e new
a i r at the inland stations.
01 d a y s 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 p a s s a g e 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
Flow i n t h e San F e r n a n d o V a l l e y a l s o
undergoes p e c u l i a r changes 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 b e g i n n i n g a t sunset ( a b o u t 1945
i n August). The e a s t e r l y o r 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
continuat i o n of the sea breeze.
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 flow up the valley f o r a large portion
o f 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
broad expanse and g e n t l e s l o p e of t h e
valley.
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 e q u i r e d 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 upon t h e i n c l i n a t i o n of t h e
valley f l o o r . T h i s is because the 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 d e p e n d u p o n t h e amount
of v e r t i c r l m o t i o n w h i c h 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 F e r n a n d o 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 of t h e h i g h
mountain a r e a s , probably 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
s m a l 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 , howe v e r , 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
the valley w i n d and t h e development of t h e
r e v e r s e flow, 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 a c c o u n t f0.r t h e l a t e e n d i n g of t h e
s e a - v a l l e y b r e e z e a t M a r c h F i e l d (RV).
(c)
E f f e c t o f the San P e d r o H i l l s . -
The Sari P e d r o W i l l s , w h i c h s u r m o u n t t h e
p o i n t o f l a n d w e s t of San P e d r o 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 c a n b e s e e n hy t h e wave
The s e a
i n t h e s t r e a m l i n e s o n F i g u r e 2.
bree%e a t Long B e a c h (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 r e m a i n s u n t i l 1430. A t S a n
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 r o m ' t h e SE, v e e r i n g g r a d u a l l y t o a
Lomita F l i g h t S t r i p
s t e a d y '3SW b y 1100.
0t o o k 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 o f t h e
predominant winds are n o t i n d i c a t e d .
At
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 0 2 3 0 a n d 05-30. T h e
s t r o n g WNW s e a b r e e z e i s p r q d o m i n a n t 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 or d e c r e a s e s c o n s i d e r a b l y i n
a m p l i t u d e 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 f r o m S a n t a M o n i c a 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
Basin is generally f r o m the east, t h a t is
i n the opposite d i r e c t i o n from t h e sea
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 s m a l l e r s p e e d , i s a f f e c t e d e v e n more by
t h e l o c a l t o p o g r a p h y . 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 ) f o l l o w e d by a d r a i n a g e
o r mountain w i n d , l a t e r r e i n f o r c e d by a
general e a s t e r l y land 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 c a l m s 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 begins, c o n t i n u i n g u n t i l
t h e 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 madify any tendency f o r a
land breeze perpendicular t o t h e shoreline.
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 s o l o n g a f t e r s u n r i s e ( 0 6 2 0 l%T
averag,: f o r A u g u s 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 w e a k e n i n g o f
t h e Ialld-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: p r e d o m i n a t e s u n t i l 0930Evrdence 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 d e t e r m i n e d by t h e c o o l i n g
of the m o u n t a i n s and t h e t o p o g r a p h y of t h e
basin, rather t h a n by t h e s e a - l a n d ternpera t u r e 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),
P a s a d e n a ( W A ) 3 O n t a r i o (Tx)l) a n d L o m i t a
!;how m o u n t a i n 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
m)
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 T e r m i n a l (Ru) and a t a b o u t
0230 a t G r a n d 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 n a r r o w p a r t of
the v a l l e y the flow a t IXX reaches g r e a t er s p e e d s t h a n a t t h e o t h e r s t a t i o n s . This
flow j o i n s a b r o a d e r e a s t e r l y flow which
crosses t h e c o a s t a l o n g S a n t a Monica Ray.
C o l d a i r From t h e San F e r n a n d o 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 M i n e s 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 w i n d a t I D n g 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 M i n e s 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 Monica Ray 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 . T h e 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 of
Signal B i l l and adjacent ridges.
This
c h a i n o f l o w h i l l s , w h i l e o n l y 2 0 0 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 s o u t h of HB ( F i g u r e 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 S a n
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 B e r n a r d i n o (DJI,) t h e n i g h t wind
a p p e a r s 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 m i d n i g h t and s t o p p i n g 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 b e t w e e n 0100
and 0300 which c h a n g e s r a t h e r a b r u p t l y t o a
SE b r e e z e . T h e n o r t h wind mav b e a mountain breeze o f f the ridges t o the north o f
the f i e l d , w h i c h 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 d o w h - v a l l e y f l o w from t h e SE. The
SE b r e e z e w e a k e ~ ss 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 somewhat 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 wind which r e a c h e s
s p e e d s o f 1 5 mph o r more b y 1 7 3 0 a n d d i minishes g r a d u a l l y t h e r e a f t e r .
By 2 3 3 0
t h e Nw w i n d s i s n o l o n g e r t h e p r e d o m i n a n t
d i r e c t i o n and a s h o r t p e r i o d of calms 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 t h e mouth of San G o r g o n i o Pass shows a
d i u r n a l wind regime q u i t e d i f f e r e n t from
the other stations.
The p r e d o m i n a n 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 a s 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 2200.
T h i s Nw w i n d
remains very s t e a d y throughout t h e n i g h t
( o v e r 70% 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 ) , but a t 0800 begins t o back
s j . o w l y , r e a c h i n g W S W by 1 1 3 0 ,
At t h i s
t i t m e t h e f u l l e f f e c t of t h e s e a - v a l l e y
b r e e z e h a s presumably r e a c h e d t h e s t a t i o n .
The s e a - v a l l e y breeze d o e s n o t remain s t e a d y
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 a n d % 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 l o w s up o n e 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
the p e r s i s t e n t northwesterly flow begins
to p r e d o m i n a t e and v e r y f e w s o u t h e r l y components o c c u r a f t e r t h a t time.
f i r i n g t h e a f t e r n o o n t h e f l o w 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 w h a t i s t e r m e d t h e " M a l o j a w i n d " ( 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 w e s t e r lit w i n d 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 p r o b a b l y 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 S p r i n g s
(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 w i n d s 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
A t 0300 a b o u t
f l o w i s p r e v a i l i n g a t TUT.
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 i v e n i n T a b l e 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 cons t a n t f l o w o f t h e h i g h e r l e v e l westerlies
through t h e p a s s . A t t h e e a s t e r n o u t l e t o f
t h e pass t h i s westerly f l o w disappears
r a p i d l y by mixing i n t o a s o u t h e a s t e r l y
flow o v e r P a l m S p r i n g s , w h e r e t h e a i r remirs c a l m 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 between r e g u l a r
pibals is t o o long t o provide data f o r
d e t a i l e d s t u d y o f t h e d i u r n a l wind-changes
aloft.
Special observations for t h i s
purpose w i l l b e d e s c r i b e d i n t h e f o l l o w i n g
sections.
DIURNAL WIND-REGIME ALOFT AT UCLA
The d i u r n a l w i n d - r e g i m e o b s e r v e d a t
U a is similar to that a t m o s t stations
i n t h e a r e a , c o n s i s t i n g o f a s e a b r e e z e from
t h e SW d u r i n g t h e a f t e r n o o n and an e a s t e r l y
o f f - l a n d wind d u r i n g 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 i m e - h e i g h t s e c t i o n o f t h e winds
o b s e r v e d a t UCLA o n 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 of t h e average 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 i c s 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 o w e s t 2000 f e e t were E
o r SE a t s s a l l s p e e d s , t y p i c a l of t h e o f f A t noon t h e s u r f a c e
l a n d n i g h t t i m e wind.
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
St a t i o n
San B e r n a r d i n o @&)
N
N
W
n
March F i e l d (RV)
Height
(msl)
D i r e c t i . o n * and Frequency
Maximum
Secondary Maximum
2500
SSE 43%
S
41%
4000
SO00
2000
N
n
N
n
n
4000
W
SO00
Palm S p r i n g s (mZ)
n
W
W
n
3040
58%
E
E
WNW
W
29%
53%
1200
33%
40%
SSE 3977
2500
5000
SSE 59%
SE 57%
* D i r e c t i o n g i v e n i n c l u d e s winds 22 l/Zo on each s i d e .
6
W
Nw 18%
33%
wsw
SW 42%
SSW 29%
w 35%
SSW 24%
ssw
25%
W 36$
UlNW 19%
DE 26%
harbinger o f t h e s e a breeze.
T h e SW s e a
breeze was w e l l d e v e l o p e d by 1330 below 2000
feet while the easterlies persisted in a
layer aloft.
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 l o w i n g
aloft.
By s h o r t l y a f t e r m i d n i g h t t h e wind
i n t h e l a y e r from 1000 t o 2000 f e e t b a c k e d
t o SE.
D u r i n g t h e e n t i r e d a y t h e w i n d s from
5000 t ( 2 1 0 , 0 0 0 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 e m p h a s i z i n g 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 d a y s , 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
b y n o 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 b e e n 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 t h 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
winds i n t h e l o w e r l e v e l s , a n d from t h e
northwest e r l i e s a l o f t .
:
?‘he d e l i n e a t i o n o f a s e a b r e e z e a n d
a l a n d b r e e z e i s n o t always 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
sea breeze, l a n d breeze, and upper flow
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
A s a n e x a m p l e , a t 1500 PWT
with height.
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
2 0 0 0 f’eet b a c k e d g r a d u a l l y t o Nw a t 8000
feet.
I t is clear that the easterly
winds 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
t h r o u g h o u t t h e d a y were p a r t o f t h e g e n e r a l
circulation.
“The w i n d 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 res u l t a n t of an e a s t e r l y component, 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
observed backing with height.
At what
l e v e l t h e l a n d w i n d 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
must 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
t o s e t up l i m i t s o f each z o n e on t h e b a s i s
o f direction.
]: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 a n d 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 b e e n drawn t o i n c l u d e t h e w i n d s
f r o m SSE to NNE i n t h e l a n d - b r e e z e z o n e ,
a n d n o r t h w i n d s i n t h e u p p e r flow.
This
is t h 2 same a s s a y i n g t h a t t h e v e c t o r component of upper flow i s considered to
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 t h e wind h a s backed t o n o r t h . I t would
perhaps be preferable to include i n t h e
l a n d wind z o n e a l l w i n d s which 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 is,
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
s u c h a d i s t i n c t i o n and f o r t h i s r e a s o n s u c h
1i 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 o r
w h e r e 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 d a s h e d l i n e s h a v e 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
w i n d s b a c k e d t h r o u g h N t o 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 ,
therefore, also arbitrary.
In t h e p r e s e n t
analyses of t i m e sections, the 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 t o 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 w i n d s i n t h e lowest l e v e l s , t o p o g r a p h y
determines t h e typical directions f o r a
given station.
For t h i s r e a s o n , i n t h e
separation o f surface directions i n t o land
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 uniform 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 a n d 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 wind arrows a r e p l o t t e d on t h e s e
diagrams b u t t h e y have been chosen t o
r e p r e s e n t the g e n e r a l c o n d i t i o n o f flow
C
h most d a y s t h e
a t t h a t l e v e l and t i m 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 cons 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 h a v e been p l o t t e d .
I f t h e w i n d s i n t h e 8000-10,000 f o o t
leyels have a d i r e c t i o n d i f f e r e n t from
t h o s e below t h e demarcation between l o c a l
sea-land b r e e z e s an upper flow can 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
can b e used.
As i n t h e c a s e o f 1 8 A u g u s t
( 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
b e t w e e n 1 2 0 U 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 from t h e g e n e r a l c i r c u l a t i o n
aloft.
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 lowest l a y e r , b u t t h e absence 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
gradual merging o f t h e local and g e n e r a l
circulation.
I n c o n t r a s t 1, 2 a n d 3
S e p t e m b e r ( F i g u r e 5 ) show d e f i n i t e boundaries o f t h e sea breeze.
Similarly the
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
of t r a n s i t i o n i s absent or is i n d i s t i n c t .
The p a t t e r n s i n F i g u r e s 4
and
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 ground 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 p r e s u m a b l y
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).
In p r a c t i c a l l y no
c a s e does t h e l a n d breeze begin a l o f t
before i t i s seen a t t h e surface.
This
r e s u l t s from t h e f a c t t h a t a d r a i n a g e
m o u n t a i n - w i n d 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 m e r g e s 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 cold l a y e r s tends t o reduce 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 b r e e z e .
N o t a s o f t e n , b u t i n many c a s e s , 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
sea breeze begins a t t h e surface.
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 over l a n d during t h e day
r.tses f a r t h e r a b o v e t h e t e m p e r a t u r e o f a i r
over s e a t h a n i t f a l l s below t h e l a t t e r
during the night.
Also, owing t o t h e quasipermanent 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 o v e r ' s o u t h e r n C a l i f o r n i a w h i c h r e s u l t s
i n a normal 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 e x c e p t 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 d a y s 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 A u g u s 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 b e t w e e n 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 marked by 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 r e g i m e
o f , a d v e c t i o n can b e d e s c r i b e d .
The m e r g i n g o f t h e s e a - l a n d w i n d
regime 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 by p e r s i s t e n t e a s t e r l y flow
above t h e sea breeze, i s u s u a l l y t h e
r e s u l t o f the thermal l o w centered over
t h e s o u t h e r n Mojave d e s e r t .
B r i n g the
r e r i o d 1-2 September, t h e thermal l o w
w a s 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 tt 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 Idaho a t 20,000 f e e t .
'fie e a s t e r l i e s a t UCLA shown o n 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 and 6000 f e e t on
these dates f i t t e d into the pattern of
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
between t h e c o a s t and t h e coast range o f
mountains.
I t w i l l b e noted t h a t above
6000 f e e t t h e w i n d s w e r e w e s t e r l y , representing t h e replacement of 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 high 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
n o r t h . 01t h e s e d a y s 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 winds c a u s e d by t h e
thermal low.
n e second p a t t e r n i s exemplified by
5 - 6 S e p t e m b e r ( s e e F i g u r e 13) a t which
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
the inland valleys of California giving
rise to westerlies or l
W'w i n d s a t 3 0 0 0 5000 f e e t a t UCLA.
In t h i s c a s e t h e s e a
At
b r e e z e m e r g e d w i t h t h e u p p e r flow.
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 I d a h o ,
and t h e e a s t e r l y w i n d s from 6000-10,00V
f e e t a r e d i f f e r e n t i a t e d from t h e winds
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 e a c h 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 flow.
The lowest and
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 by 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 by 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 a n d sea. T h i s 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 and t h e
ocean a r e a immediately adj acent to t h e
coast.
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 w i n d p a t t e r n , c o n t r o l l e d by t h e
thermal l o w , and n o t confined t o t h e
coastal plain.
I t a f f e c t s t h e flow i n l a n d
a s f a r as t h e c e n t e r o f t h e southwestern
d e s e r t . On p a r t i c u l a r d a y s t h e t h e r n i a l 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 daytime 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 has a diurnal cycle o f
c h a n g i n g i n t e n s i t y , b u t a t times 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 t h a n o n e
day. T h e d i u r n a l wind regime p r o d u c e d h a s
been c a l l e d a c o n t i n e n t - o c e a n wind (2).
At such 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 on-shore
f l o w 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
a p p r o a c h e s 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 w h i c h
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
of t h e coast l i n e o r t h e desert thermal
l o w p r e v a i l s above t h e monsoonal.winds.
n e l e i s o r d i n a r i l y a gradual merging
o f each o f t h e s e p a t t e r n s i n t o t h e one
above i t , b u t on c e r t a i n days t h e l i m i t s
o f each l a y e r can be d e f i n i t e l y seen.
AVERAGE DIURNAL WIND TIME-SECTION AT UCLA
The a v e r a g e d i u r n a l wind regime i n
h e i g h t and t i m e h a s been 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 rep r e s e n t i n g summer, f a l l and w i n t e r s e a s o n s .
These diagrams have been 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 w i n d d i r e c t i o n a n d
f o r c e f o r each 5 0 0 - 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.
?he 45' s e c t o r 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 d e t e r m i n e d t h e p r e d o m i n a n t
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 time and
l e v e l and 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 t h e arrow.
Men another 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 of 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 r o w i s shown
a n d l a b e l e d w i t h t h e number o f cases. The
w i n d 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 and i s a rough average
d e t e r m i n e d by v i s u a l i n s p e c t i o n o f t h e
tally.
T h i s method o f r e p r e s e n t i n g t h e
d o m i n a n t 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 the advantage of 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 c o m p l e t e
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 a n d t i m e s a r e p r e s e n t e d i n
The roses w i l l a l l o w t h e
F i g u r e s 7 t o 9.
r e a d e r t o check f o r h i m s e l f t h e p r e d o m i n a n t
d i r e c t i o n s summarized i n t h e average
diurnal time-sections.
A l l data used 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.
T h e a v e r a g e time s e c t i o n s h a v e b e e n
analyztzd i n t h e same manner 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
c o m p a r i s o n s b e t w e e n s e a s o n s may b e 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
have the following characteri-stics i n
common.
I n t h e l o w e s 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 r o m 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 evening and e a r l y
morning.
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
shortest i n the winter.
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,
a p p e a r s t o b e ' a b o u t 5000 f e e 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 e a s t e r 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 time
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 predominant i n t h e lowest l a y e r s
t h r o u g h o u t t h e n i g h t and e a r l y morning,
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 m i d n i g h t 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
the r e l a t i v e l y small depth of the e a s t
w i n d b e t w e e n 0000 a n d 0 3 0 0 P W i n d i c a t e s
that t h i s feature isprobably characteristic
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
area. Similarly, 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
seasons s u g g e s t s t h a t t h i s i s a l s o charact er 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 timesections corroborate the findings of the
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 wind 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 has been
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 tempera t u r e and a d e c r e a s e o f r e l a t i v e humidity
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 of t h e
land breeze."
I n t h e Los A n g e l e s B a s i n ,
t h e d i u r n a l wind c h a n g e s 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 regime 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 p r o m i n e n t s u b s i d e n c e
inversion.
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
feet.
.
Similar to the t i m e sections for
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 land breeze is s t i l l blowing 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 l e s s d i s t i n c t .
I t w i l l be noted t h a t i n the average
p i c t u r e t h e s e a breeze v e e r s s l i g h t l y with
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 mentioned i n s p e c t i o n o f i n d i v i d u a l days 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
with height.
The t u r n i n g c a n n o t b e exp l a i n e d b y a d v e c t i o n o f t h e t r o u g h of t h e
temperature inversion because i t occurs
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 .
The observed 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
addition of vectors representing the
decreased e f f e c t of t h e land-sea breeze
regime w i t h h e i g h t and t h e merging w i t h
9
t:he u p p e r f l o w 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 e m p e r a t u r e
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 for each
1000-foot l e v e l .
Even w i t h t h e . c l o s e
n e t w o r k 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 1 9 4 4 , 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 b e made b e c a u s e
Ithe t e m p e r a t u r e a n d 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 w e r e n o 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 radiosonde.
At 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 lowest l e v e l s the easterlies a r e s t i l l
b l o w i n g 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 h a p p e n s t o a l e s s e r d e g r e e when
t h e l a n d wind 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 d e p t h o f t h e s e a b r e e z e a t
t h e expense of t h e countercurrent a l o f t
f i t s t h e t h e o r y of t h e s e a - l a n d regime
most g e n e r a l l y a c c e p t e d ( I ) , (3).
The
countercurrent a l o f t l a s t s longer a t Batavia
(3) t h a n i n t h e Los A n g e l e s B a s i n , b u t a t
F e l i x s t o w , England t h e a v e r a g e d e p t h 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 B a t a v i a s t u d y showed
that the effect of the countercurrent
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 m e r g e
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 e x c e e d i n g 6000 feet. However, i f t h e p r e v a i l i n g
w i n d a l o f t w e r e weak a s i n t h e c a s e a t
B a t a v i a , the land-sea winds p r p b a b l y would
b e shown a t l e v e l s h i g h e r t h a n 6000 f e e t .
As p r e f i o u s l y explained, t h e t u r n i n g o f
w i n d w i t h h e i g h t i n d i c a t e s t h a t some coniponent o f t h e l a n d - s e a regime i s o f t e n
d i s c e r n i b l e above 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.
H a v i n g 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 wind changes 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 t h e c h a n g e s on one p a r t i c u l a r day p r o v e s
interesting.
AREAL PATTERN ON AN INDIVTDUAL DAY
To make a t h r e e - d i m e n s i o n a 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 d a y , t h e
c o o p e r a t i o n of c e r t a i n AAF w e a t h e r s t a t i o n s
was e n l i s t e d .
On 5 - 6 S e p t e m b e r 1944, s i x
s t a t i o n s i n t h e Los A n g e l e s 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 r e
shown i n F i g u r e s 10 and 11.
The d a y 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 e n d 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 f o e h n c o n d i t i o n c a u s e d by
t h e d e v e l o p m e n t of a h i g h - p r e s s u r e c e n t e r
o v e r t h e G r e a t Basin,
T h e t i m e - h e i g h t p a t t e r n o f t h e sea
a n d 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 given by the s o l i d , o r dashed 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 2 4 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 l a n d wind i n t h e l o w e s 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 S e p t e m b e r , t h e t h e r m a 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 s e e n on F i g u r e
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 I d a h o . T h e r e were no f r o n t s
i n the western United S t a t e s during the
period.
I n s p e c t i o n of t h e U U A t i m e - s e c t i o n 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 2000-5000 f e e t
p e r s i s t e d f r o m 1500 o n t h e 5 t h t o noon of
t h e 6th.
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 t h e r m a l l o w .
C i r c u l a t i o n around t h e thermal l o w can
b e s e e n a t 5 0 0 0 f e e t a t 0 3 0 0 PWT o n 6
S e p t e m b e r ( 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 w e r e e a s t e r l y , now c o n t r o l l e d b
the Great Basin high.
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 geographic picture of the develop+
ment of t h e l o c a l - w i n d p a t t e r n , t h e c r o s s
section of Figure 12 i s presented.
I
r e p r e s e n t s a p r o f i l e from t h e c o a s 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 from t h e c o a s t .
Va
Nuys (DVN) l i e s i n t h e San F e r n a n d o 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 flowing i
from 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 ex
p l a i n e d i n t h e d i s c u s s i o n o f F i g u r e 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 u s e d t o p l a c e DVN and IW o n t h e
profile.
A t 1800 PWT o n 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 u p p e r p o r t i o n o
F i g u r e 1 2 shows t h e development of t h
1
I
l a n d wind from 1900 t o 0 1 0 0 . A t 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
e a s t e r l y 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 u p t o 1500 f e e t a t U U A , DVN
and IJUA, b u t westerlies a r e s t i l l o c c u r r i n g
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 winds a t s t a t i o n s l a y i n g n e a r t h e
cross-section l i n e .
?he lower s e t of p r o f i l e s i n F i g u r e 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 of
e a s t e r l y wind r e p r e s e n t e d by t h e a r e a below
It
t h e p r o f i l e l i n e s o f 0300 and 0600.
w i l l be noted t h a t t h e l a n d wind began n e a r
t h e c o a s t and worked i n l a n d , i n c r e a s i n g i n
depth f a s t e s t over the inland s t a t i o n s .
The f i r s t p i b a l showing a n y l a n d wind
above L4 was 0300 a s c a n be s e e n on F i g u r e
10. This l a t e b e g i n n i n g 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 i g u r e 1.
A t 0900 t h e l a n d wind i s d e v e l o p e d a t
a l l s t a . t i o n s b u t LA shows a s e a b r e e z e up
t o llQO f e e t and a l a y e r of 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 1 3 0 0
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
e x c e p t 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 h o u r a t
LA and UCZA a t 1500 f e e t , and a t 3000 f e e t
a t DVN, w h 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 present a t
(2000 t o
4200 f e e t ) and a t DO1 (3500 t o above 5000
feet).
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
geographically a s the p r o f i l e indicates.
REFERENCES
f i e Cali fornia S t r a t u s I n v e s t i g a t i o n
o f 1944 by N e i b u r g e r , Beer, and
L e o p o l d ; 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 M e t e o r o l o g i c a l @nunittee.
Local Winds; Weather D i v i s i o n Report
# 9 8 2 , Hq Army A i r F o r c e s , F e b r u a r y
1945 ( R e s t r i c t e d )
Tropical Land and Sea Breezes;
( B r i t i s h ) Naval M e t e o r o l o g i c a l Branch,
hlemo 126, 1944 ( R e s t r i c t e d ) .
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
Ministry, Synoptic Division Technical
Memo #SS, 1943.
(Reprinted U.S. Navy,
NAVAER 50-IR-$2, August 1944)
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