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s band
Journal of Atmospheric and Terrestrial PhlsltS, 1963, Vol 25, pp 23 to 34 Perg tmon Pres~ Ltd Printed in Northern Ireland
The SUnrLSe and sunset effects on the level of atmospherics activity on the 27 kc/s band M W CHIPLONKAR and R N KAREKAR Department of Physics, Umverslty of Poona, India
(Rece~wd 11 September 1962) Abstract--The sunmse and sunset effects on the level of atmospheric~ on 27 kc/~ ale studied for the I G Y and the I G C periods at a tropical station The two effects ale not obserx cd to be symmetrical The latest llnnt of the beginning and tile earhest hmlt of the end of the nunlike fall oecm about l0 iilln after g~ound sunrme at the ~tahon A rumple explanation is offered for thlb, ~hlch also explains the other IImlts of the start and the end of the sunrise fall In the case of the sunset rlse the stalt is seen to take place almost always after ground sunset In summer frequently a dlp m activity is obsel red near gi ound sunset Both these are re~ponslble fol the asymmetry On the average the fall from the day ~ide obey~ a cosine law up to the mmmlum aftel whmh there is a nteep rise for one hour follou ed b~ a sudden change m the slope to a low value Aspart oftheIGY and theIGC programme at thm~tatmn (Poona 18 31'N, 73 52'E) ~ e have been recording continuously the level of atmobphene~ activity on 27 kc/~ band (Band~ldth 200 e/s) during the permd January 1958-September 1959 Fol this puipobe the lecelxel ciiemt suggested by ELHSON (1955) which recorded mteglated lntenslty wlth a time constant of 60 see was u~ed, wlth only shght modn~icahons An lnx erred L-type of aerial and an Evershed and Vlgnoles pen recorder were employed The lesults of our obselvahon~ on the mIdmght effect and on the SEA have already been ~eported and dlscussed m two separate eonllnunlcatlon% CtIIPLONKAI~, ]~]~_REIZAR a n d MAR~'ADI (1962), ('HI]?LOb!KAI~ a n d KA~tEKAIa* (1962) I n ~}ilq c o m m u n i c a t i o n ~ e p r e s e n t t h e r e s u l t s o f s t a h s t m a l analy~lb o f t h e d a t a o n t h e ~unH~e a n d s u n s e t effects o b s e r v e d at this s t a t i o n F o r t h e bake o f ¢ o n ~ e m e n c e , t h e s e m e d e a l t ~ l t h m t~ o separate sectmns SECTION A
T h e su~r~se
effect
A c c o m ) ~ G to Chapman's theory of the production of the ionosphere, sola~ ~adlatmn ~s the mare source of ~on-formatlon The changes m it at the t~me of sunnse and sunset, will naturally be accompamed by changes in lOnlsatmn winch ~ 111 be indicated by changes in the different physmal propeltms of the layels The exact t~mes of occurrence of these effects however, often do not coincide w~th ground sunrise o~ even with layer-sunrise For instance WATTS (1952) finds that the sunrise effect at the height of reflectmn for 300 kc/s for obhque incidence occurs when ~ays graze the ozonosphere BROW~ and PETRIE (1954) have found that for an obhque reflechon height for 16 kc/s, the sunrme effect occms one hem before ground sunrme In the case of E-layer ;omsatmn, the effect sometimes occurs ariel ground sunrise (BANAL 1955, ~ELLS 1949) and sometimes before ground smnme (BANAL 1955, A]~PLETO~ and I~A~SM~TH 1935) ]~ARAL maintains that the sunrise effect fo~ vertmal incidence for E- and _F-layer heights of maximum lOmSatmn * In th~ paper all other expemmental
details axe g~x en 23
24
M W CtIIPLONKAtland R N KAR,EKAtt
occurs when sunrise takes place in the m g ht time layer, after the solar rays pass, at least, above the height of the da y side m a x i m u m m m s a t m n of the region H e finds t h a t the delay of the sunrise effect, for a height of m a x i m u m lomsatmn from the actual layer sunrise is a bout 40-50 mln for E -l ayer and greater t h a n 1 hr for F-layeI BRAC]~W~LL and BA~- (1952) have e a r n e d out field strength measurements of a 16 kc/s t r a n s m i t t e r at different distances T h e y found t h a t for oblique incidence (at 535 km), field strength as well as a p p a r e n t height staTt falhng suddenly before sunrise (at solar zenith angle 98 °) and are a mmxmum at ground sunrise and sunset, symmetrical about noon, 1 e 1225 horns L M'T Also at a distance of 200 k m from the t l a n s m l t t e r the v a n a t m n is found to be symmetrical a b o u t 25 m m after noon B u t at veltlcal mmdence the fall m height stairs just at sunrise and follows the "log sec (z)" law T h e y have explained these observations by assuming two layers below the E-layer, D~ and Dz, Dz-layer being a small distance below D~-]ayer I n c l d e n t l y :BRACEWELL (1952) has f m t h e l elaborated this t h e m y b y assuming D~ to be an exhaustion t y p e layel (1 e the laye~ on which fu r th er mmdcnce of r adl at m n does not add to its mmsatmn) to explain solar flale effects and BAIN (1953) has supported it SACHDEV (lq58) wolkmg at Deltn on atmospherics received on 27 ke/s and 100 kc/s has found t h a t the tnne of decJease of a t m o s p h e u c s noxse is equally s c a t t m ed about the local sunnse LUC:EO~ ~ (1947) has studmd the seasonal var m t l on of the d m a t l o n of the fall of the a t m o s p h e u c s activ ity and found it to be similar to t hat of the dlffelence bet~ een the tram of the sunuse at the E - l a ye r and at ground I~IEKER (1960) has studmd the sm m se effect on atmospherics at 27 kc/s in great details using a radm gom om et el Accoldlug to him mg h t time reception via E-layel (100 kin) is m t e u u l ) t e d when the solar lays to u ch the radm wave p a t h on the easteln ~lde at a height of 75 km (D-layer) after grazing the ozonosphere at a height of 28 km He has f m t h e r explanled the " s a t e ] h t e " uses in act i vi t y after the first fall, on the basis of t~anment i)ropagatmn ~xlth some of the reflections flora the D-layer He has pointed to the possll)lhty of ~eflactlon of waves while passing through the feel)ly mmsed ~egmn t)etween the D- and E-layers, which m a y help to explain the d m a t m n of the fall Wlnle accordmg to W m T s o x (1961) no existing t h e o r y explains the sunllse effect ou VLF p~opagatlon, pa~hcularly ~ts f l e que nc y dei)endence
Rc,~ults obtained at Poon~ W ith a view to studying the sunnse effect, we. also, have analysed om lecords obtained during the period J a n u a l y 195S-September 1959 The fall was clemly obselved on 325 days and was not so well detectable on 50 days d m m g this period (see Fig 1) For each day. the times of start and end of the sunnse fall and its duration were read from the ~ecords of these 325 days T ~ o sep~uate scatter diagrams ~ ere pl ot t ed for (1) the time of s tal t and (2) the tmle of end of the sumlse fall, against the d a y (Fig 2) I t should be pointed out t h a t the n u m b e r of readings ~wulable m 1958 (wz 113) is less t h a n t h a t m 1959 (wz 212) because of the bette~ sen s ltlwty of the recorder used m 1959 as compared to the one used in 1958 The times of local g l o u n d sunrise are also indicated on these dmgrams fm each day, which form a continuous curve as shown in this figure The scatter (hagrams clea~ly show t h a t there is a defimte line of d e m a r k a t m n between the tram of s t a l t
T h e s u n r i s e a n d s u n s e t effects o n t h e level of a t m o s p h e r m s a c t l w t y
J
r
Sunrise
fali
25
GSS
E
s ,
,
4
I
L
,
,
5
.
.
6
. . 7
.
.
. 8
17
Sunset i
GSR
Sunrise
foil
,
rise ,
,
,
,
'I
I
,
E
dip
Sunset
I3 ~
I
L I'
"-+
,,
! I : I I,
5
6
I,
~ I , I I
7
8 I , , ~ 1 , ,
5
t~,,
i1,1
I
6
GSR
,
[ Sunset
[
r
I 6
I~
I •
', t
I
8
9
I
J
8
GSS
'
,
I
6
i,
~
,
7
il 9
I ' 1 , 1
~
,
dip I
8
,
L
II
:
9
,C
F i g 1 P o r t i o n s of o m g m a l r e e o r d s m d m a t m g t y p m a l s u n n a e a n d ~unset effects o n 27 ke/~ Ordinates represen6 integrated fieldstrength m arbltrmy umts ~--Start, G S R - - G r o u n d Sunrise, E~End, G S S --Gi ound Sunset I - - S u n r l b e fall s t a I t s a t g I o u n d sunmse a n d e n d s a f t e l a v e I y s b m t d u r a t i o n o f 3 0 r a m o n l y (20 9 1959) I I - - S u n r B e fall s t a r t s before g r o u n d sunrme a n d e n d s 75 m m a f t e r it (8 4 1959) I I I - - S u n m a e fall w i t h a v e r y l o n g d u r a t i o n , a r a r e occasmon (23 8 1959) I V - - T h i s w i n t e r t y p e o f s u n s e t rise s t a r t s n e a l l y 2½ h r a f t e r g I o u n d s u n s e t (30 12 1958) V - - T h e m m m m m o f s u n s e t d i p is v e I y n e a r g r o u n d s u n s e t N o t e t h e p o s i t r o n ofthekmk (1581959) V I - - T h e m l n m m m o f s u n s e t dip is 43 h r a f t e r g r o u n d s u n s e t N o t e t h e p o s i t i o n of t h e k i n k (20 8 1959)
26
M W ('HIPLONKAI~and R N KAI~EI~AI~
a n d t h e t i m e of e n d of t h e sunrise fall This line p r a c t m a l l y coincides w i t h t h e line of local g r o u n d sunrise To be m o l e precise it is a b o u t l0 mln after local g r o u n d sunrise, p a r t m u l a r l y m 1959 I n 1958, h o w e v e r , the fixing of this t i m e is n o t so v e r y e x a c t This m e a n s t h a t neglecting t h e few e x c e p t i o n s t h e s t a r t of t h e fall can, at t h e latest, o c c u r at n e a r l y the local g r o u n d sunrise a n d the end of fall can o c c u r at the earliest, at n e a r l y the same time I n o t h e r wotds, if we a s s u m e t h a t t h e fall is due to increase m t h e a b s o l p t i o n of the s k y w a v e s of a t m o s p h e r i c s , the a b s o r p t i o n s t a r t s latest at t h e local g r o u n d sunrise A 0400
1958
0500
I
•/
~.
I,M
, [ t
I,A
i,o
/
I,A ,s 1,0
•
,,~.~•l o•
, .2~( /
•
}~
•
• •
I
.
".
"J
.~" "" ~ \. * * "," : *L
I ,F
* , l]•
1959
I,M
,,A
,.s
#
* *_.If* *~
/~, • • =./~-
I,M
,,A
:
•
'\\°
I,D
I,J
0800
.~..~.
• ;',.
I ,N
l,J
0700
*== ='~'/
I
:
I
0600
/Z'"
// • /
0700
i *.
•
,s
q,M
E3
0600
/
/
\.
*
t,;:,,l' &,m,~e.
.j:
e
" .o~-
/*
*%.d~
*
* It I *'~'s
• ~...": "-:I,\"
~;..:
*#,~,
~ .:.;%....~:." ...~{ ,
GSR
GSR
F i g 2 S c a t t e r d i a g r a m o f (A) t i m e o f s t r u t a n d (B) tram o f e n d o f s u m l s e fM1 o n 27 ke/~ a g a i n s t t h e d a y
D~6c7188~0~ To t h e best of our k n o w l e d g e no such a t t e m p t a t a detailed analysm of t h e sunrise fall has so far been carried o u t a n d f u r t h e r m o r e such a well defined line of d e m a r k a t m n b e t w e e n t h e s t a r t a n d t h e end of this p h e n o m e n o n has n o t been noticed F o r instance, In SACHDEV S w o r k m e n t i o n e d above, he has n o t s t a t e d w h e t h e r his t i m e s refer t o t h e s t a i r or t h e end of t h e sunrise fall or to their m e a n I f it is the m e a n , the result is m a c c o r d a n c e w i t h our obsezvations A c c o r d i n g to LVGEON (1929) a t m o s p h e r i c s get e l i m i n a t e d moze a n d m o r e as the s u m i s e t a k e s place at the source ~esponsible for those a t m o s p h e r i c s The
T h e sunrise a n d s u n s e t effects on t h e level o f a t m o s p h e r i c s actl~ ~ty
27
sunrise fall s t a r t s earlier or l a t e r d e p e n d i n g on w h e t h e r t h e source of a t m o s p h e r i c s is to t h e east or west of the receiver, r e s p e c t i v e l y B u t still he observes the fall to s t a r t always before t h e local g r o u n d sunrise RIEKER'S e x p l a n a t i o n of his o b s e l v a t l o n s gives t h e l a t e s t t i m e of s t a r t of t h e sunrise effect for t h e m o s t d i s t a n t w e s t e i n source, which could be received b y a single hop in c o n f o r m i t y with our o b s e r v a t i o n B u t it does not expl,un out obsetr a t t a n of t h e e a r h e s t t i m e of the end of t h e fall A c c m d m g to his e x p l a n a t i o n t h e e a r h e s t e n d could occur a short t i m e a f t e r t h e local g r o u n d sunrise at the source-point 1vlng f a r t h e s t e a s t w a r d which could be received b y a single hop W e shall t r y to explain in w h a t follows the hne of d e m a r k a t i o n at a b o u t suml~e, m e n t i o n e d ~bove, m a simple ~ a y As a first aI)proxim~tlon ~ e shall considm only the single hop r e c e p t i o n (see Fig 3) Then, for a n y ,ecelvet position
IonosphericIoyer
UL) Fig 3 An E a s t - W e s t seetmn through the station and the centre of the earth d r a w n for e x p l a i n i n g t h e h n e o f d e m a r k a t i o n b e t w e e n ~tart a n d e n d o f t h e ~ulll lse fall in a t m o q p h e n e a aett~ l t y on 27 ke/~
R the~e exist two f a r t h e s t s o m c e s S 1 a n d S a flora which waves cau be ~eceived. via the Ieflectlng l a y e r T h e p a t h of p r o p a g a t i o n of t h e waves f r o m b o t h points will be t a n g e n t i a l at R N e x t we a s s u m e t h a t t h e a b s o r p t i o n of the w a v e s t a r t s w h e n a n y p i t t ot t h e p a t h of t h a t w a v e is e x p o s e d to solm ~ays a n d a b s o r p t i o n goes on increasing as a g r e a t e r a n d greate~ p a r t o f the p a t h IS e x p o s e d to sola~ rays, finally the a b s o r p t i o n reaches a m a x i m u m w h e n t h e c o m p l e t e p a t h is e x p o s e d to solar r a y s N o u t h e e m h e s t s t a r t a n d t h e e n d of a t m o s p h e r i c s a c t i v i t y will be t h a t due to S 1 a n d the l a t e s t will be t h a t due to S, This leads to e x a c t l y w h a t we f o u n d O b v i o u s l y the local g r o u n d sunrise is the i n s t a n t of d e m a r k a t i o n b e t w e e n the start and end of the sunrise fall T h e u p p e r h m t t to t h e s t a r t a n d t h e lower limit to the end of sunrise fall ate also p l e s e n t in the s c a t t e i d i a g r a m This p o i n t is b r o u g h t out more cleally b y t h e h i s t o g r a m , m Fig 4, of t h e difference b e t w e e n t h e t i m e of local g r o u n d sunrtse a n d the t i m e of s t a r t of sunrise fall I t shows t h a t t h e fall, at the earliest, sta, ts a b o u t 11 hr before t h e local g r o u n d sunrise Calculations of t h e u p p e r limit of the s t a r t wete m a d e according to t h e a b o v e a s s u m p t i o n s I f the height of t h e
28
M W
CtlIPLONI~IAR a n d ]Z N
I~AI~EKA~
reflecting l a y e r is t a k e n to be 90 k m (GARD:NEg a n d PAWSEY 1953, WAIT 1960) a n d t h e E a r t h ' s r a d i u s 6378 k m t h e u p p e r l i m i t c o m e s o u t to be 1.27 hr, w h i c h c o m p a r e s quite well w i t h t h e o b s e r v e d l i m i t F i g 4 also shows a mmilar h i s t o g r a m d~awn for t h e e n d of t h e sunrise fall I t shows t h a t t h e lower l i m i t o f t h e e n d is also 90 m m a f t e r t h e local g r o u n d sunrise B u t ff we neglect t h e first 10 m m , for t h e r e a s o n to be g i v e n later, this t i m e c o m e s o u t to be a b o u t 80 m m T h i s m e a n s t h a t for t h e source S 2 t h e h e i g h t of reflection is lower t h a n t h a t for S~ B u t t h e s e limits are n o t as well m a r k e d as is t h e line o f d e m a r k a t i o n n e a r t h e local g r o u n d sunrise This is so b e c a u s e o f t h e f a c t t h a t b o t h t h e s t a r t a n d t h e e n d h a v e a t e n d e n c y to c o n c e n t r a t e t h e p o i n t s on t h e s c a t t e r d i a g r a m , n e a r e r a n d n e a r e r t h e local g r o u n d sunrise line as t h e source p o i n t a p p l o a e h e s t h e receiver, a n d in p r a c t i c e , s u c h n e a r e r sources are m o r e effective M o r e o v e r for all t h e e a s t e r n sources t h e
120
80
40
F-I I , I , I 0 -50 -15 0 3o oo Mm
eo
q,
! I o
,
I , , 3o 60
,% 90
-~
Min
Fig 4 Histograms of time (hfferenee between local ground sunrise and (A) start, (B) end of sunrise fall in activity on 27 kc/s e n d should occur, a c c o r d m g to t h e a b o v e a s s u m p t i o n s , a t t h e local g r o u n d sunrise a t R a n d sources on t h e w e s t e r n side only, will c r e a t e t h e s c a t t e r for t h e e n d p o i n t s T h e a b o v e e x p l a n a t i o n is o n l y a p p r o x i m a t e as f a c t o r s h k e d o u b l e or m u l t i p l e h o p r e c e p h o n as also t h e d e p e n d e n c e on r e l a t i v e d i r e c t i o n o f source are n o t c o n m d e r e d B u t as f a r as t h e results a b o u t t h e llnnts (as s t a t e d a b o v e ) are conc e r n e d t h e s e f a c t o r s a p p e a r to affect t h e m v e r y httle, especially since t h e c o n d i t i o n s of t a n g e n c y a t R a l w a y s hold As f a r as t h e l a t e s t s t a r t of t h e sunrise fall is c o n c e r n e d I{IEKER'S e x p l a n a t i o n s e e m s to r e p r e s e n t t h e f a c t s m o r e a c c u r a t e l y as it r e q m r e s t h e solar r a y s to t o u c h the D-layer after grazing the ozonosphere whmh thelefore, explains the observed lag o f t h e s t a r t f r o m t h e local g r o u n d s u n n s e b y a b o u t 10 m m B u t a t t h e s a m e t i m e we feel t h a t one m o r e f a c t o r - - r e l a x a t i o n t r a m of l O m S a t m n - - m u s t also be p a r t l y r e s p o n m b l e for t h e lag I t is well k n o w n t h a t t h e r e l a x a t i o n t i m e for t h e D - l a y e r is ot t h e o r d e r of 8 m m as f o u n d f r o m t h e solar flare o b s e r v a t i o n s (MITRA a n d JONES 1953, ELLISO~" 1953) This p o i n t was a p p a r e n t l y o v e r l o o k e d b y o t h e r s I{IEK~a e x p l a i n s t h e d u r a t i o n of t h e fall as due to t h e m m s a t l o n b e t w e e n t h e D - a n d E - l a y e r s W e feel t h a t , t h o u g h t h e m m s a t l o n in a n d a b o v e t h e D - l a y e r p l a y s a l a r g e r p a r t , t h e m m s a t m n below t h e / ) - l a y e r m u s t also be p l a y i n g s o m e
The
Table
1
~unmse
Duratmn
and
sunset
m
minutes
Feb
Mar
effects
of
on
the
the
fall
m
level
of
actlwty
atmospherics
at
activity
~umlse
Carrmr
29
band
27
ke/s
\ Date
~[onth \
1958 Jan
Apr
15
60
.
120
53
.
. .
.
.
1
--
'2
--
3
.
4
--
--
5
--
O0
75
--
0
--
50
45
.
.
7
May
.
-
. --
.
.
.
.
75
55
40
-.
40
30
--
27
.
q
--
45
40
33
23
10
--
--
b5
95
30
40
11
--
50
35
--
50
.
12
--
--
--
15
13
---
15
55
--
14
-
23
--
--
20
.
10
.
17
38
.
IS
. ]5
.
54)
.
lq
60
45
47
30
45
.
21
45
.
22
65
--
2~
40
.
2t
35
--
25
105
.
2b
23
.
27
-
21";
.
.
.
53
--
30
02
.
3l
30
.
A~ erage
47
45
. . .
35 75
bo
.
.
. 49
.
.
.
. .
00
. .
.
. 51
.
/q)5 -
.
.
.
42 . 45
--
So
- -
qq)
43
lo 10
- .
.
47 .
2~ --
58
.
22
()5
.
. .
.
.
- -
.
.
- -
105
. .
70
.
.
.
. .
.
15 5o
.
.
45 .
43
-
{)7
---
'~IS
.
- -
q()
t)()
.
.
-
(~()
. .
.
30
- -
.
. .
--
48
.
.
.
. q5
45
-.
.
7o
.
45
.
--
.
05
-
55
.
.
. .
.
.
17
-
55
--
{)()
.
.
.
.
. .
45
--
--
.
. .
.
.
.
. .
30
.
29
.
.
.
--
.
30 .
. 55
.
37
--
.
.
.
15
.
-
.
.
.
-
Dee
.
55
.
60
.
30
. .
.
30
.
.
q0 135
.
.
.
.
.
.
20
.
75 5o
.
. .
15 25
.
.
.
.
.
2O
.
. .
.
65
Nov
--
.
---
Oct
45
. .
22
-.
.
.
--
.
.
45
.
--
.
--
.
~0
22
.
40
.
.
--
.
Sep
.
.
---
Aug .
.
--
--
lul
.
S
15
-
Jun
.
. 4l
33
-
1 ~5
.
lo5
43 .
~,5
105 .
40
. (G
1)5
7')
52
\ Dato
\
Month ""\x
lqSq ,Inn
F( b
Mar
ADr
Ma\
1
--
45
25
14
2
--
30
34
() 5
30
40
Ira,
]ul 45
-
-
--
\ua
S, l)
87
(,5
( ) -I
55
45
q7
3
30
--
4
60
-
-
27
45
75
--
77
42
I /
5
31
---
15
75
--
--
32
bO
2l
()
40
1 "i
25
35
37
83
t8
50
120
50
40
24
55
16
45
2S'i
20
7
80
60
40
30
8
52
--
75
40
'~0
9
40
22
38
45
30
65
4q
43
10
45
20
98
80
20
23
45
25
45
50
00
41
l 5
~i
97
52
ll
m
30
M W
CItIPLONKAg
R
and
Table
1
N KAI~EKA-~
(eont)
\ Date ~
l~lonth Jan
t~eb
Mar
Apr
1959 May
Jun
Jul
Aug
Sop
12 13 14 15 lb
----75
85 25 30 40 45
40 --51 20
45 50 37 100 37
20 40 35 12tt 45
30 75 18 lS 27
45 22 44 32 43
3~ 76 52 39 4O
~3 30 4l (~l TS
17 18 19 20 21
85 60 -60 82
-35 25 15 45
45 30 29 77 50
60 -45 45 -
3O
--58 35 O0
28
9O 40 -120 b0
4o 5S
45 ~)11
40 40 100 45 38
22 23 24 25 26
75 30 60 45 15
75 45 15 -35
68 -68 28 25
-
23 ~4 2S --
-19 35 l0 4O
15 42 ~(P 1110 ~,~
33 228 33 105 28
27 28 29 30 31
60 -35 45 --
------
37 68 95 50 35
00 -2'2 50
5O S 75
34 3~ 105 -
90 --35 75 49
~2 37 75 4 () 31
A~ erage
5"t
43
41
5(I
It
4~
54
15
4(t 5t)
30 54
45
80
°..o/
"
I I d F
I M
\
-\/2/
/
I A M J
J
..
I. A
I. S
I I I ..I O N D J
1958 Fig
5
Annual
V&tlatlon
I F
I I M A
I M
I d
I J
l 1 A S
1959 of the
duration
m
mnmte~
o f bun~l~;e
fall
on
27 kr/.
p a r t a n d h e n c e thin also m u s t be t a k e n into a c c o u n t while e x p l a i n i n g t h e t o t a l d u r a t i o n of t h e fM1 I n o r d e r to s t u d y t h e seasonal v a r i a t i o n of t h e d u r a t i o n of t h e sunllbe fall a g r a p h of m o n t h l y a v e r a g e d u r a t i o n a g a i n s t t h e c o r r e s p o n d i n g m o n t h ]s d r a w n in F i g 5 (see T a b l e 1) T h e a v e r a g e d u r a t i o n for t h e t o t a l p e r i o d u n d e r e o n s l d e l a t l o n is 49 rain I t shows a m i n i m u m m J u n e a n d l e e b r u a t y LUGEO?¢ (1047) h o w e v e r r e p o r t s a m i n i m u m m t h e e q u i n o x m o n t h s for t h e E u r o p e a n l a t i t u d e s
The sunrise and sunset) effects on the level of atmospherics act~vltv
31
SECTION ~B
The sunset effect On the basis of the t h e o r y for t h e sunrise effect, t h e r e should also be a corresponding sunset effect of a reverse ordeI I n fact. it has been o b s e r v e d b y different workers t h a t the sunset has a similar effect on the h m g h t of the ionosphere, its 1on-density, etc BRACEWELL a n d BAIze (1952) r e p o r t e d a n s e m the a p p a r e n t height of reflection while receiving R u g b y signals on 16 kc/s B u t the case of the a t m o s p h e r i c s is more c o m p h c a t e d because of the n u m e r o u s u n k n o w n a n d distribu t e d s o m c e s F u r t h e r it is m o l e often m a s k e d b y o t h e r p h e n o m e n a hke the local t h u n d e l s t o r m a c t i v i t y a n d the D - l a y e r a b s o r p t i o n Results and d~scusswu I n o r d e r to s t u d y the sunset effect, our records of the 27 kc/s b a n d were c a l e f u l l y r e a d I t was o b s e r v e d t h a t in general the low level of a t m o s p h e r i c s a c t l w t y d u r i n g the d a y g r a d u a l l y increased to a hagh night v a l u e n e a r the t i m e of sunset T h e e x a c t t u n e of s t a r t of the sunset rise m a c t i v i t y , as well as its end. were n o t e d d o w n f r o m the daffy records for all the d a y s on whmh these could be cleally o b s e r v e d I n fact it was f o u n d to be difficult to locate t h e m , m a n y t~mes no such defimte effect was observable, being o b s c m e d b y t h e s t o r m s To locate t h e end was still more dnTicult because on m a n y days, t h e a c t i v i t y w e n t on n s m g up to m i d n i g h t This effect could be clearly o b s e r v e d only on a b o u t 150 d a y s as against the s u n n s e effect w h i c h was distract on 325 d a y s during the same period D u e to the less sensitive r e c o r d e r used in 1958, t h e available d a t a weIe c o n e s p o n d i n g l y less d u r i n g this y e a r A s c a t t e r d i a g r a m (Fig 6) of t h e t i m e of s t a r t of the sunset rise was p l o t t e d against the d a y T h e o n l y p o i n t b r o u g h t o u t b y this d m g r a m is t h a t on a g r e a t e r n u m b e r of occasmns it o c c u r r e d a f t e r sunset t h a n before it B u t it did not follow d e f i m t e l y the sunset hne t h r o u g h t h e seasons as in the case of t h e s u n u s e effect I t was seen to occur as late as two hr o2 m o r e a f t e r the local g r o u n d sunset These o b s e I v a t l o n s are o b v i o u s l y n o t a c c o u n t a b l e on the basis of t h e a s s u m p t i o n s m a d e for the e x p l a n a t i o n of t h e sunrise effect T h e a v e r a g e d u r a t i o n of t h e sunset rise is 65 min N e x t , t h e s u p e r p o s e d epoch m e t h o d of analysis was used I n s u m m e r p a i t m u larly, a well m a r k e d chp is s o m e t i m e s o b s e r v e d n e a r sunset, s o m e t i m e s before a n d sometm~es a f t e r Such a dip n e a r sunset, m s u m m e r , is o b s e r v e d m t h e average a t m o s p h e r i c s a c t i v i t y b y m a n y workers (LvGEON 1947, BUREAU 1929, WATSOX ~VATT 1926. MACKERROW 1960, H_XRWOOD 1958) T h e lowest p o i n t of this dq) was selected as the zero-epoch Of course, o n l y those days were selected on which such a dip could be o b s e r v e d satisfactorily T h e readings of the a c t i v i t y wele n o t e d f r o m the daily c h a r t s for 3 hi on eithel sade of it, a t an i n t e r v a l of 15 m m F o r t y - f o u l good sets of readings were available f r o m which an a v e I a g e c u r v e was d r a u n (Fig 7 a n d T a b l e 2) T h e c u r v e n a t u l a l l y shows a well m a r k e d dip, b u t it also brings o u t one more mgmficant p o i n t T h e fall f r o m the day-slde is v e r y g r a d u a l a n d similar to a cosine v a r a a t m n B u t the rise is linear a n d steep, up to 60 rain, a f t e r the d i p - m i n i m u m a n d t h e n it s u d d e n l y changes the slope to a v e r y low v a l u e which ~s m a i n t a i n e d up to the end I n c i d e n t l y this rise t i m e of 60 min is
32
M ~,V (~HIPLONKABand R N KAICEKAI¢ IST
1730
1830
I,F
1930
.
1958
2030
i.
~
*
• *
. •
eQ ~ %
•
•
•
I,M
• .
I,A
• .o
*
•
',M I,J
$
l,d
.
I,A
•
IN ID ,959
%,o
.. • |
•
•
.
•
I
•
o.. " ,M IA
Id
°
°•
°•5
#
ii /.?:
•
•
°. .
1,5
.
•~
,
•
.
°
IO Flg
6 Scattm dmglmn of tnne of ~tmt oi sunset H~e on 27 kc/s against the (lay
n e a r l y e q u a l to t h e tmle d u r a t i o n w h m h is f o u n d for t h e a v m a g e sunset ~lse, vm 65 m m This m a y indicate the general v a h d l t y of the results of the f o r m e r m e t h o d also I t s h o u l d be noted, however, t h a t the dip m i n i m a o c c u r r e d before the g r o u n d sunset on t w e n t y - o n e oeeasmns a n d after it on t h i r t y - o n e occasions Also t h e m a x i m u m d e p a r t u r e f r o m the sunset line is a b o u t 30 min I t was seen t h a t the fall of the a v e r a g e c u r v e is mmflar to "cos (t)" v a r i a t i o n a n d so t h e c u r v e of "cos (t)" was superposed, w i t h suitable scales, on the fMhng side of t h e dip (the p o i n t s m a r k e d - x - x - in Fig 7), b u t the zero ot t h e "cos (t)" was t a k e n a t the p o i n t where t h e e x t r a p o l a t e d fM1, cuts t h e plus b0 rain o r d i n a t e Thts p o i n t was t a k e n because it was t h o u g h t t h a t this p o i n t is the real end of the c u r v e as m d m a t e d b y t h e kink in the n s m g side of the dip I t can be seen t h a t t h e eommdenee is v e r y e x a c t F u t h e r m o r e ff the zero of "cos (t)" is t a k e n to comrade w i t h t h e p o i n t of m i n i m u m of the dip (range of " t " m a d e to covet 3 hr
The summe and sunset eft(et~ on the lex el of atmosphelwb actLvJty
33
Table 2 Average dlff.rentlal amplitudes for 3 hr before and after the n m m n u m (epoch) at %nn~et Time from el)od~ (ram)
Amphtude* (ram.)
--180 165 150
!3 9 14 3 14 2
--135 120 - 105
13 8 13 6 13 2
q0
11 8
- 75
10 4
(d)
8 7
--45 --30 --15
69 4q 24
degree
80
04
15 30 45
37 76 10 7
60 75 90
14 4 15 4 16 6
105 120 135
16 5 16 5 17 2
150 1()5 180
17 9 18 5 18 8
~0
C
90
Q~e~ /~
-IC
,
-180
0
5C
0
- 120
--
-6q
3
•
0
t()
120
180
Mr'
F i g 7 Average sunset-dq) vamatmn on 27 ke/.~ (- - ) and cos (t) v a n a t m n ( t - t - c ) auperpo~ed on c a d l othel
* One m m is approxlmatel 3 equal to 12 5 / , V / m / 1 ke/~ b a n d ~ l d t h c o r r e s p o n d i n g l y ) t h e n t h e c o i n c i d e n c e is g o o d o n l y f o r "t" g r e a t e r t h a n a b o u t 30 °, b u t p o i n t s f o r " t ' l e s s t h a n 30 ° h e a l i t t l e a b o v e c u r v e o f t h e f a l l The explanahon of these obselved facts about the dip, paitlcularly that of " c o s ( t ) " v a r i a t i o n , d o e s n o t a p p e a r t o b e r u m p l e L t ' G E O ~ ' S (1947) e x p l a n a t m n t h a t t h e d i p IS p a l t l y d u e t o t h e v a r l a t a o n o f t h u n d e r s t o r m a c t i v i t y a n d p a l t l y to the D-layer absorption seems to be vahd to a certain extent The kink of the nsmg pair may be due to the D-1wer ceasing to absorb T h e e x p l a n a t i o n o f t h e s u n s e t d~p g i v e n b y JOUAUST ( ] 9 4 6 ) d e p e n d s u p o n t h e v a r i a t i o n o f t h e p s e u d o - B r e w s t e r a n g l e o f t h e a o n o s p h e r e d u e t o c h a n g e s in l O n l s a t l o n
34
M W CItIPLONKAR and g
N KAI~EKAR
at of on is
the time of sunset This would suggest that the variation on both ides the minimum must be smooth However, the kink in Fig 7 is difficult to explam this hypothesis unless some other phenomenon llke a diffeient reflecting layel assumed to be connected with the mlmmum Belie concluding this discussion it would be wmthwhlle mentioning one mote point regarding the phenomenon oi a dip nl the level of V L F mgna]s observed at sunl]se HAI~GREAYES (1962) h a s e x p l a i n e d t h i s o n t h e b a s i s o f a t e m p o r a i y enhancement of ionisation reaching a hlghei value than the eqmhbnum one at the ionosphenc sunrise In the D~-layer H e m e n t i o n s t h a t a n e x a m i n a t i o n ot 1,9 6 k c / s t r a n s m i s s i o n s r e c o r d e d a t i a n g e s o f 378 a n d 528 k i n b y t h e R a d i o R e sealch Station. Slough, has levealed a temporary leductlon of leflection height at s u n l ] s e A s i m i l a r e f f e c t is a l s o n o t e d i n t h e a t m o s p h e l i c s actl~ ] t y o n 27 k c / s b o t h a t s u m m e a n d s u n s e t i n a f e w o f t h e m o n t h l y c u i v e s ~ e p o ~ t e d b y B V e E A U (1929) ~EFERENCES A]'I~LETON E V and NAIS~ITtt R ]~AIN W C BmaAL S S BI~ACEWELL R :N BI~ACE~ELL 1% N and BAIN W C BROWN S B and PETRIE W BI/REAU iq
CI-IIPLONKAI%~¢[ %V CHIPLONKA~ M W , and MA~WADI P ELLISO~ M A E~LiSON M A GAICDNEI% F F and 1LIARGREAVE%J ]~ HAI~WOOD J JOUA~rST R
and KAttEKAtt R N KA~EKA~ R N R
:PAWSEY J L
1935 1953 1955 1952 1952 1954 1929 1962 1962
_Proc Roy Soc A150, 685 J Atmosph Te~ l'hys 8, 141 J Atmosph Ter~ 1)hys 6, 160 J Atmosph TeTr Phys 2, 226 J Atmosph Terr l't~y~ 2, 216 Canad J Pl~ys 82, 90 C R Acad Sc~ , ])a~zs December I~d,an J Met (;eot)hy~ 18, ,July J Atmosph Terr 1)l~ys 24, 9
1953 1955 1953 1962 1958 1946
J Atmosph Tear Phy~ 4, 226 U g S I I n f m m a t l o n Bulletin No 92 J Atmosph Tett Phys 3, 321 J Atmosph Terr Phys 24, 1 lboc lust Elect Enqts 105B, 293 L'Ionosphere, pp 179-217, Pam~ (cited b y B~ace~ ell and Barn) Tnage a p a r t de :tnnule~ de la stahun ~et~trale Sutsse de meteoroloff~qu¢ C R Acad Set I'ar~s 188, 1690 J Gcopt~ls Res 65, 1911 J Atmo~t,t~ Tear l'hy,~ 4, 141 .Ph I) t]~cst~ (1 Eeole pol 3 teehmque Fedcrale, Zumeh) J N( ~ Industt Res 17A, 262 J (¢eophys Res 65, 1939 J Geophys Res 57, 487 E x p ~VHelebs & \~ nele~s Engr , 8, 234 J Geophys Rcs 54, 277 l l e p o t t S R I p r o j ( c t No 3171 Stanfold 1%eseareh Institute, Cahfornm
LuGEO~ J
1947
h~CKEm~OW C A MIT~A A P and JONES R E RIEKE~ J
1929 1960 1953 1960
SACHDEV D K WAIT J ]% WATTS J M ~rATSO~ ~VATT 1% A WELLS H ~V WI:[ITSON ~,~ L
1958 1960 1952 1926 1949 1961
The SUnrLSe and sunset effects on the level of atmospherics activity on the 27 kc/s band M W CHIPLONKAR and R N KAREKAR Department of Physics, Umverslty of Poona, India
(Rece~wd 11 September 1962) Abstract--The sunmse and sunset effects on the level of atmospheric~ on 27 kc/~ ale studied for the I G Y and the I G C periods at a tropical station The two effects ale not obserx cd to be symmetrical The latest llnnt of the beginning and tile earhest hmlt of the end of the nunlike fall oecm about l0 iilln after g~ound sunrme at the ~tahon A rumple explanation is offered for thlb, ~hlch also explains the other IImlts of the start and the end of the sunrise fall In the case of the sunset rlse the stalt is seen to take place almost always after ground sunset In summer frequently a dlp m activity is obsel red near gi ound sunset Both these are re~ponslble fol the asymmetry On the average the fall from the day ~ide obey~ a cosine law up to the mmmlum aftel whmh there is a nteep rise for one hour follou ed b~ a sudden change m the slope to a low value Aspart oftheIGY and theIGC programme at thm~tatmn (Poona 18 31'N, 73 52'E) ~ e have been recording continuously the level of atmobphene~ activity on 27 kc/~ band (Band~ldth 200 e/s) during the permd January 1958-September 1959 Fol this puipobe the lecelxel ciiemt suggested by ELHSON (1955) which recorded mteglated lntenslty wlth a time constant of 60 see was u~ed, wlth only shght modn~icahons An lnx erred L-type of aerial and an Evershed and Vlgnoles pen recorder were employed The lesults of our obselvahon~ on the mIdmght effect and on the SEA have already been ~eported and dlscussed m two separate eonllnunlcatlon% CtIIPLONKAI~, ]~]~_REIZAR a n d MAR~'ADI (1962), ('HI]?LOb!KAI~ a n d KA~tEKAIa* (1962) I n ~}ilq c o m m u n i c a t i o n ~ e p r e s e n t t h e r e s u l t s o f s t a h s t m a l analy~lb o f t h e d a t a o n t h e ~unH~e a n d s u n s e t effects o b s e r v e d at this s t a t i o n F o r t h e bake o f ¢ o n ~ e m e n c e , t h e s e m e d e a l t ~ l t h m t~ o separate sectmns SECTION A
T h e su~r~se
effect
A c c o m ) ~ G to Chapman's theory of the production of the ionosphere, sola~ ~adlatmn ~s the mare source of ~on-formatlon The changes m it at the t~me of sunnse and sunset, will naturally be accompamed by changes in lOnlsatmn winch ~ 111 be indicated by changes in the different physmal propeltms of the layels The exact t~mes of occurrence of these effects however, often do not coincide w~th ground sunrise o~ even with layer-sunrise For instance WATTS (1952) finds that the sunrise effect at the height of reflectmn for 300 kc/s for obhque incidence occurs when ~ays graze the ozonosphere BROW~ and PETRIE (1954) have found that for an obhque reflechon height for 16 kc/s, the sunrme effect occms one hem before ground sunrme In the case of E-layer ;omsatmn, the effect sometimes occurs ariel ground sunrise (BANAL 1955, ~ELLS 1949) and sometimes before ground smnme (BANAL 1955, A]~PLETO~ and I~A~SM~TH 1935) ]~ARAL maintains that the sunrise effect fo~ vertmal incidence for E- and _F-layer heights of maximum lOmSatmn * In th~ paper all other expemmental
details axe g~x en 23
24
M W CtIIPLONKAtland R N KAR,EKAtt
occurs when sunrise takes place in the m g ht time layer, after the solar rays pass, at least, above the height of the da y side m a x i m u m m m s a t m n of the region H e finds t h a t the delay of the sunrise effect, for a height of m a x i m u m lomsatmn from the actual layer sunrise is a bout 40-50 mln for E -l ayer and greater t h a n 1 hr for F-layeI BRAC]~W~LL and BA~- (1952) have e a r n e d out field strength measurements of a 16 kc/s t r a n s m i t t e r at different distances T h e y found t h a t for oblique incidence (at 535 km), field strength as well as a p p a r e n t height staTt falhng suddenly before sunrise (at solar zenith angle 98 °) and are a mmxmum at ground sunrise and sunset, symmetrical about noon, 1 e 1225 horns L M'T Also at a distance of 200 k m from the t l a n s m l t t e r the v a n a t m n is found to be symmetrical a b o u t 25 m m after noon B u t at veltlcal mmdence the fall m height stairs just at sunrise and follows the "log sec (z)" law T h e y have explained these observations by assuming two layers below the E-layer, D~ and Dz, Dz-layer being a small distance below D~-]ayer I n c l d e n t l y :BRACEWELL (1952) has f m t h e l elaborated this t h e m y b y assuming D~ to be an exhaustion t y p e layel (1 e the laye~ on which fu r th er mmdcnce of r adl at m n does not add to its mmsatmn) to explain solar flale effects and BAIN (1953) has supported it SACHDEV (lq58) wolkmg at Deltn on atmospherics received on 27 ke/s and 100 kc/s has found t h a t the tnne of decJease of a t m o s p h e u c s noxse is equally s c a t t m ed about the local sunnse LUC:EO~ ~ (1947) has studmd the seasonal var m t l on of the d m a t l o n of the fall of the a t m o s p h e u c s activ ity and found it to be similar to t hat of the dlffelence bet~ een the tram of the sunuse at the E - l a ye r and at ground I~IEKER (1960) has studmd the sm m se effect on atmospherics at 27 kc/s in great details using a radm gom om et el Accoldlug to him mg h t time reception via E-layel (100 kin) is m t e u u l ) t e d when the solar lays to u ch the radm wave p a t h on the easteln ~lde at a height of 75 km (D-layer) after grazing the ozonosphere at a height of 28 km He has f m t h e r explanled the " s a t e ] h t e " uses in act i vi t y after the first fall, on the basis of t~anment i)ropagatmn ~xlth some of the reflections flora the D-layer He has pointed to the possll)lhty of ~eflactlon of waves while passing through the feel)ly mmsed ~egmn t)etween the D- and E-layers, which m a y help to explain the d m a t m n of the fall Wlnle accordmg to W m T s o x (1961) no existing t h e o r y explains the sunllse effect ou VLF p~opagatlon, pa~hcularly ~ts f l e que nc y dei)endence
Rc,~ults obtained at Poon~ W ith a view to studying the sunnse effect, we. also, have analysed om lecords obtained during the period J a n u a l y 195S-September 1959 The fall was clemly obselved on 325 days and was not so well detectable on 50 days d m m g this period (see Fig 1) For each day. the times of start and end of the sunnse fall and its duration were read from the ~ecords of these 325 days T ~ o sep~uate scatter diagrams ~ ere pl ot t ed for (1) the time of s tal t and (2) the tmle of end of the sumlse fall, against the d a y (Fig 2) I t should be pointed out t h a t the n u m b e r of readings ~wulable m 1958 (wz 113) is less t h a n t h a t m 1959 (wz 212) because of the bette~ sen s ltlwty of the recorder used m 1959 as compared to the one used in 1958 The times of local g l o u n d sunrise are also indicated on these dmgrams fm each day, which form a continuous curve as shown in this figure The scatter (hagrams clea~ly show t h a t there is a defimte line of d e m a r k a t m n between the tram of s t a l t
T h e s u n r i s e a n d s u n s e t effects o n t h e level of a t m o s p h e r m s a c t l w t y
J
r
Sunrise
fali
25
GSS
E
s ,
,
4
I
L
,
,
5
.
.
6
. . 7
.
.
. 8
17
Sunset i
GSR
Sunrise
foil
,
rise ,
,
,
,
'I
I
,
E
dip
Sunset
I3 ~
I
L I'
"-+
,,
! I : I I,
5
6
I,
~ I , I I
7
8 I , , ~ 1 , ,
5
t~,,
i1,1
I
6
GSR
,
[ Sunset
[
r
I 6
I~
I •
', t
I
8
9
I
J
8
GSS
'
,
I
6
i,
~
,
7
il 9
I ' 1 , 1
~
,
dip I
8
,
L
II
:
9
,C
F i g 1 P o r t i o n s of o m g m a l r e e o r d s m d m a t m g t y p m a l s u n n a e a n d ~unset effects o n 27 ke/~ Ordinates represen6 integrated fieldstrength m arbltrmy umts ~--Start, G S R - - G r o u n d Sunrise, E~End, G S S --Gi ound Sunset I - - S u n r l b e fall s t a I t s a t g I o u n d sunmse a n d e n d s a f t e l a v e I y s b m t d u r a t i o n o f 3 0 r a m o n l y (20 9 1959) I I - - S u n r B e fall s t a r t s before g r o u n d sunrme a n d e n d s 75 m m a f t e r it (8 4 1959) I I I - - S u n m a e fall w i t h a v e r y l o n g d u r a t i o n , a r a r e occasmon (23 8 1959) I V - - T h i s w i n t e r t y p e o f s u n s e t rise s t a r t s n e a l l y 2½ h r a f t e r g I o u n d s u n s e t (30 12 1958) V - - T h e m m m m m o f s u n s e t d i p is v e I y n e a r g r o u n d s u n s e t N o t e t h e p o s i t r o n ofthekmk (1581959) V I - - T h e m l n m m m o f s u n s e t dip is 43 h r a f t e r g r o u n d s u n s e t N o t e t h e p o s i t i o n of t h e k i n k (20 8 1959)
26
M W ('HIPLONKAI~and R N KAI~EI~AI~
a n d t h e t i m e of e n d of t h e sunrise fall This line p r a c t m a l l y coincides w i t h t h e line of local g r o u n d sunrise To be m o l e precise it is a b o u t l0 mln after local g r o u n d sunrise, p a r t m u l a r l y m 1959 I n 1958, h o w e v e r , the fixing of this t i m e is n o t so v e r y e x a c t This m e a n s t h a t neglecting t h e few e x c e p t i o n s t h e s t a r t of t h e fall can, at t h e latest, o c c u r at n e a r l y the local g r o u n d sunrise a n d the end of fall can o c c u r at the earliest, at n e a r l y the same time I n o t h e r wotds, if we a s s u m e t h a t t h e fall is due to increase m t h e a b s o l p t i o n of the s k y w a v e s of a t m o s p h e r i c s , the a b s o r p t i o n s t a r t s latest at t h e local g r o u n d sunrise A 0400
1958
0500
I
•/
~.
I,M
, [ t
I,A
i,o
/
I,A ,s 1,0
•
,,~.~•l o•
, .2~( /
•
}~
•
• •
I
.
".
"J
.~" "" ~ \. * * "," : *L
I ,F
* , l]•
1959
I,M
,,A
,.s
#
* *_.If* *~
/~, • • =./~-
I,M
,,A
:
•
'\\°
I,D
I,J
0800
.~..~.
• ;',.
I ,N
l,J
0700
*== ='~'/
I
:
I
0600
/Z'"
// • /
0700
i *.
•
,s
q,M
E3
0600
/
/
\.
*
t,;:,,l' &,m,~e.
.j:
e
" .o~-
/*
*%.d~
*
* It I *'~'s
• ~...": "-:I,\"
~;..:
*#,~,
~ .:.;%....~:." ...~{ ,
GSR
GSR
F i g 2 S c a t t e r d i a g r a m o f (A) t i m e o f s t r u t a n d (B) tram o f e n d o f s u m l s e fM1 o n 27 ke/~ a g a i n s t t h e d a y
D~6c7188~0~ To t h e best of our k n o w l e d g e no such a t t e m p t a t a detailed analysm of t h e sunrise fall has so far been carried o u t a n d f u r t h e r m o r e such a well defined line of d e m a r k a t m n b e t w e e n t h e s t a r t a n d t h e end of this p h e n o m e n o n has n o t been noticed F o r instance, In SACHDEV S w o r k m e n t i o n e d above, he has n o t s t a t e d w h e t h e r his t i m e s refer t o t h e s t a i r or t h e end of t h e sunrise fall or to their m e a n I f it is the m e a n , the result is m a c c o r d a n c e w i t h our obsezvations A c c o r d i n g to LVGEON (1929) a t m o s p h e r i c s get e l i m i n a t e d moze a n d m o r e as the s u m i s e t a k e s place at the source ~esponsible for those a t m o s p h e r i c s The
T h e sunrise a n d s u n s e t effects on t h e level o f a t m o s p h e r i c s actl~ ~ty
27
sunrise fall s t a r t s earlier or l a t e r d e p e n d i n g on w h e t h e r t h e source of a t m o s p h e r i c s is to t h e east or west of the receiver, r e s p e c t i v e l y B u t still he observes the fall to s t a r t always before t h e local g r o u n d sunrise RIEKER'S e x p l a n a t i o n of his o b s e l v a t l o n s gives t h e l a t e s t t i m e of s t a r t of t h e sunrise effect for t h e m o s t d i s t a n t w e s t e i n source, which could be received b y a single hop in c o n f o r m i t y with our o b s e r v a t i o n B u t it does not expl,un out obsetr a t t a n of t h e e a r h e s t t i m e of the end of t h e fall A c c m d m g to his e x p l a n a t i o n t h e e a r h e s t e n d could occur a short t i m e a f t e r t h e local g r o u n d sunrise at the source-point 1vlng f a r t h e s t e a s t w a r d which could be received b y a single hop W e shall t r y to explain in w h a t follows the hne of d e m a r k a t i o n at a b o u t suml~e, m e n t i o n e d ~bove, m a simple ~ a y As a first aI)proxim~tlon ~ e shall considm only the single hop r e c e p t i o n (see Fig 3) Then, for a n y ,ecelvet position
IonosphericIoyer
UL) Fig 3 An E a s t - W e s t seetmn through the station and the centre of the earth d r a w n for e x p l a i n i n g t h e h n e o f d e m a r k a t i o n b e t w e e n ~tart a n d e n d o f t h e ~ulll lse fall in a t m o q p h e n e a aett~ l t y on 27 ke/~
R the~e exist two f a r t h e s t s o m c e s S 1 a n d S a flora which waves cau be ~eceived. via the Ieflectlng l a y e r T h e p a t h of p r o p a g a t i o n of t h e waves f r o m b o t h points will be t a n g e n t i a l at R N e x t we a s s u m e t h a t t h e a b s o r p t i o n of the w a v e s t a r t s w h e n a n y p i t t ot t h e p a t h of t h a t w a v e is e x p o s e d to solm ~ays a n d a b s o r p t i o n goes on increasing as a g r e a t e r a n d greate~ p a r t o f the p a t h IS e x p o s e d to sola~ rays, finally the a b s o r p t i o n reaches a m a x i m u m w h e n t h e c o m p l e t e p a t h is e x p o s e d to solar r a y s N o u t h e e m h e s t s t a r t a n d t h e e n d of a t m o s p h e r i c s a c t i v i t y will be t h a t due to S 1 a n d the l a t e s t will be t h a t due to S, This leads to e x a c t l y w h a t we f o u n d O b v i o u s l y the local g r o u n d sunrise is the i n s t a n t of d e m a r k a t i o n b e t w e e n the start and end of the sunrise fall T h e u p p e r h m t t to t h e s t a r t a n d t h e lower limit to the end of sunrise fall ate also p l e s e n t in the s c a t t e i d i a g r a m This p o i n t is b r o u g h t out more cleally b y t h e h i s t o g r a m , m Fig 4, of t h e difference b e t w e e n t h e t i m e of local g r o u n d sunrtse a n d the t i m e of s t a r t of sunrise fall I t shows t h a t t h e fall, at the earliest, sta, ts a b o u t 11 hr before t h e local g r o u n d sunrise Calculations of t h e u p p e r limit of the s t a r t wete m a d e according to t h e a b o v e a s s u m p t i o n s I f the height of t h e
28
M W
CtlIPLONI~IAR a n d ]Z N
I~AI~EKA~
reflecting l a y e r is t a k e n to be 90 k m (GARD:NEg a n d PAWSEY 1953, WAIT 1960) a n d t h e E a r t h ' s r a d i u s 6378 k m t h e u p p e r l i m i t c o m e s o u t to be 1.27 hr, w h i c h c o m p a r e s quite well w i t h t h e o b s e r v e d l i m i t F i g 4 also shows a mmilar h i s t o g r a m d~awn for t h e e n d of t h e sunrise fall I t shows t h a t t h e lower l i m i t o f t h e e n d is also 90 m m a f t e r t h e local g r o u n d sunrise B u t ff we neglect t h e first 10 m m , for t h e r e a s o n to be g i v e n later, this t i m e c o m e s o u t to be a b o u t 80 m m T h i s m e a n s t h a t for t h e source S 2 t h e h e i g h t of reflection is lower t h a n t h a t for S~ B u t t h e s e limits are n o t as well m a r k e d as is t h e line o f d e m a r k a t i o n n e a r t h e local g r o u n d sunrise This is so b e c a u s e o f t h e f a c t t h a t b o t h t h e s t a r t a n d t h e e n d h a v e a t e n d e n c y to c o n c e n t r a t e t h e p o i n t s on t h e s c a t t e r d i a g r a m , n e a r e r a n d n e a r e r t h e local g r o u n d sunrise line as t h e source p o i n t a p p l o a e h e s t h e receiver, a n d in p r a c t i c e , s u c h n e a r e r sources are m o r e effective M o r e o v e r for all t h e e a s t e r n sources t h e
120
80
40
F-I I , I , I 0 -50 -15 0 3o oo Mm
eo
q,
! I o
,
I , , 3o 60
,% 90
-~
Min
Fig 4 Histograms of time (hfferenee between local ground sunrise and (A) start, (B) end of sunrise fall in activity on 27 kc/s e n d should occur, a c c o r d m g to t h e a b o v e a s s u m p t i o n s , a t t h e local g r o u n d sunrise a t R a n d sources on t h e w e s t e r n side only, will c r e a t e t h e s c a t t e r for t h e e n d p o i n t s T h e a b o v e e x p l a n a t i o n is o n l y a p p r o x i m a t e as f a c t o r s h k e d o u b l e or m u l t i p l e h o p r e c e p h o n as also t h e d e p e n d e n c e on r e l a t i v e d i r e c t i o n o f source are n o t c o n m d e r e d B u t as f a r as t h e results a b o u t t h e llnnts (as s t a t e d a b o v e ) are conc e r n e d t h e s e f a c t o r s a p p e a r to affect t h e m v e r y httle, especially since t h e c o n d i t i o n s of t a n g e n c y a t R a l w a y s hold As f a r as t h e l a t e s t s t a r t of t h e sunrise fall is c o n c e r n e d I{IEKER'S e x p l a n a t i o n s e e m s to r e p r e s e n t t h e f a c t s m o r e a c c u r a t e l y as it r e q m r e s t h e solar r a y s to t o u c h the D-layer after grazing the ozonosphere whmh thelefore, explains the observed lag o f t h e s t a r t f r o m t h e local g r o u n d s u n n s e b y a b o u t 10 m m B u t a t t h e s a m e t i m e we feel t h a t one m o r e f a c t o r - - r e l a x a t i o n t r a m of l O m S a t m n - - m u s t also be p a r t l y r e s p o n m b l e for t h e lag I t is well k n o w n t h a t t h e r e l a x a t i o n t i m e for t h e D - l a y e r is ot t h e o r d e r of 8 m m as f o u n d f r o m t h e solar flare o b s e r v a t i o n s (MITRA a n d JONES 1953, ELLISO~" 1953) This p o i n t was a p p a r e n t l y o v e r l o o k e d b y o t h e r s I{IEK~a e x p l a i n s t h e d u r a t i o n of t h e fall as due to t h e m m s a t l o n b e t w e e n t h e D - a n d E - l a y e r s W e feel t h a t , t h o u g h t h e m m s a t l o n in a n d a b o v e t h e D - l a y e r p l a y s a l a r g e r p a r t , t h e m m s a t m n below t h e / ) - l a y e r m u s t also be p l a y i n g s o m e
The
Table
1
~unmse
Duratmn
and
sunset
m
minutes
Feb
Mar
effects
of
on
the
the
fall
m
level
of
actlwty
atmospherics
at
activity
~umlse
Carrmr
29
band
27
ke/s
\ Date
~[onth \
1958 Jan
Apr
15
60
.
120
53
.
. .
.
.
1
--
'2
--
3
.
4
--
--
5
--
O0
75
--
0
--
50
45
.
.
7
May
.
-
. --
.
.
.
.
75
55
40
-.
40
30
--
27
.
q
--
45
40
33
23
10
--
--
b5
95
30
40
11
--
50
35
--
50
.
12
--
--
--
15
13
---
15
55
--
14
-
23
--
--
20
.
10
.
17
38
.
IS
. ]5
.
54)
.
lq
60
45
47
30
45
.
21
45
.
22
65
--
2~
40
.
2t
35
--
25
105
.
2b
23
.
27
-
21";
.
.
.
53
--
30
02
.
3l
30
.
A~ erage
47
45
. . .
35 75
bo
.
.
. 49
.
.
.
. .
00
. .
.
. 51
.
/q)5 -
.
.
.
42 . 45
--
So
- -
qq)
43
lo 10
- .
.
47 .
2~ --
58
.
22
()5
.
. .
.
.
- -
.
.
- -
105
. .
70
.
.
.
. .
.
15 5o
.
.
45 .
43
-
{)7
---
'~IS
.
- -
q()
t)()
.
.
-
(~()
. .
.
30
- -
.
. .
--
48
.
.
.
. q5
45
-.
.
7o
.
45
.
--
.
05
-
55
.
.
. .
.
.
17
-
55
--
{)()
.
.
.
.
. .
45
--
--
.
. .
.
.
.
. .
30
.
29
.
.
.
--
.
30 .
. 55
.
37
--
.
.
.
15
.
-
.
.
.
-
Dee
.
55
.
60
.
30
. .
.
30
.
.
q0 135
.
.
.
.
.
.
20
.
75 5o
.
. .
15 25
.
.
.
.
.
2O
.
. .
.
65
Nov
--
.
---
Oct
45
. .
22
-.
.
.
--
.
.
45
.
--
.
--
.
~0
22
.
40
.
.
--
.
Sep
.
.
---
Aug .
.
--
--
lul
.
S
15
-
Jun
.
. 4l
33
-
1 ~5
.
lo5
43 .
~,5
105 .
40
. (G
1)5
7')
52
\ Dato
\
Month ""\x
lqSq ,Inn
F( b
Mar
ADr
Ma\
1
--
45
25
14
2
--
30
34
() 5
30
40
Ira,
]ul 45
-
-
--
\ua
S, l)
87
(,5
( ) -I
55
45
q7
3
30
--
4
60
-
-
27
45
75
--
77
42
I /
5
31
---
15
75
--
--
32
bO
2l
()
40
1 "i
25
35
37
83
t8
50
120
50
40
24
55
16
45
2S'i
20
7
80
60
40
30
8
52
--
75
40
'~0
9
40
22
38
45
30
65
4q
43
10
45
20
98
80
20
23
45
25
45
50
00
41
l 5
~i
97
52
ll
m
30
M W
CItIPLONKAg
R
and
Table
1
N KAI~EKA-~
(eont)
\ Date ~
l~lonth Jan
t~eb
Mar
Apr
1959 May
Jun
Jul
Aug
Sop
12 13 14 15 lb
----75
85 25 30 40 45
40 --51 20
45 50 37 100 37
20 40 35 12tt 45
30 75 18 lS 27
45 22 44 32 43
3~ 76 52 39 4O
~3 30 4l (~l TS
17 18 19 20 21
85 60 -60 82
-35 25 15 45
45 30 29 77 50
60 -45 45 -
3O
--58 35 O0
28
9O 40 -120 b0
4o 5S
45 ~)11
40 40 100 45 38
22 23 24 25 26
75 30 60 45 15
75 45 15 -35
68 -68 28 25
-
23 ~4 2S --
-19 35 l0 4O
15 42 ~(P 1110 ~,~
33 228 33 105 28
27 28 29 30 31
60 -35 45 --
------
37 68 95 50 35
00 -2'2 50
5O S 75
34 3~ 105 -
90 --35 75 49
~2 37 75 4 () 31
A~ erage
5"t
43
41
5(I
It
4~
54
15
4(t 5t)
30 54
45
80
°..o/
"
I I d F
I M
\
-\/2/
/
I A M J
J
..
I. A
I. S
I I I ..I O N D J
1958 Fig
5
Annual
V&tlatlon
I F
I I M A
I M
I d
I J
l 1 A S
1959 of the
duration
m
mnmte~
o f bun~l~;e
fall
on
27 kr/.
p a r t a n d h e n c e thin also m u s t be t a k e n into a c c o u n t while e x p l a i n i n g t h e t o t a l d u r a t i o n of t h e fM1 I n o r d e r to s t u d y t h e seasonal v a r i a t i o n of t h e d u r a t i o n of t h e sunllbe fall a g r a p h of m o n t h l y a v e r a g e d u r a t i o n a g a i n s t t h e c o r r e s p o n d i n g m o n t h ]s d r a w n in F i g 5 (see T a b l e 1) T h e a v e r a g e d u r a t i o n for t h e t o t a l p e r i o d u n d e r e o n s l d e l a t l o n is 49 rain I t shows a m i n i m u m m J u n e a n d l e e b r u a t y LUGEO?¢ (1047) h o w e v e r r e p o r t s a m i n i m u m m t h e e q u i n o x m o n t h s for t h e E u r o p e a n l a t i t u d e s
The sunrise and sunset) effects on the level of atmospherics act~vltv
31
SECTION ~B
The sunset effect On the basis of the t h e o r y for t h e sunrise effect, t h e r e should also be a corresponding sunset effect of a reverse ordeI I n fact. it has been o b s e r v e d b y different workers t h a t the sunset has a similar effect on the h m g h t of the ionosphere, its 1on-density, etc BRACEWELL a n d BAIze (1952) r e p o r t e d a n s e m the a p p a r e n t height of reflection while receiving R u g b y signals on 16 kc/s B u t the case of the a t m o s p h e r i c s is more c o m p h c a t e d because of the n u m e r o u s u n k n o w n a n d distribu t e d s o m c e s F u r t h e r it is m o l e often m a s k e d b y o t h e r p h e n o m e n a hke the local t h u n d e l s t o r m a c t i v i t y a n d the D - l a y e r a b s o r p t i o n Results and d~scusswu I n o r d e r to s t u d y the sunset effect, our records of the 27 kc/s b a n d were c a l e f u l l y r e a d I t was o b s e r v e d t h a t in general the low level of a t m o s p h e r i c s a c t l w t y d u r i n g the d a y g r a d u a l l y increased to a hagh night v a l u e n e a r the t i m e of sunset T h e e x a c t t u n e of s t a r t of the sunset rise m a c t i v i t y , as well as its end. were n o t e d d o w n f r o m the daffy records for all the d a y s on whmh these could be cleally o b s e r v e d I n fact it was f o u n d to be difficult to locate t h e m , m a n y t~mes no such defimte effect was observable, being o b s c m e d b y t h e s t o r m s To locate t h e end was still more dnTicult because on m a n y days, t h e a c t i v i t y w e n t on n s m g up to m i d n i g h t This effect could be clearly o b s e r v e d only on a b o u t 150 d a y s as against the s u n n s e effect w h i c h was distract on 325 d a y s during the same period D u e to the less sensitive r e c o r d e r used in 1958, t h e available d a t a weIe c o n e s p o n d i n g l y less d u r i n g this y e a r A s c a t t e r d i a g r a m (Fig 6) of t h e t i m e of s t a r t of the sunset rise was p l o t t e d against the d a y T h e o n l y p o i n t b r o u g h t o u t b y this d m g r a m is t h a t on a g r e a t e r n u m b e r of occasmns it o c c u r r e d a f t e r sunset t h a n before it B u t it did not follow d e f i m t e l y the sunset hne t h r o u g h t h e seasons as in the case of t h e s u n u s e effect I t was seen to occur as late as two hr o2 m o r e a f t e r the local g r o u n d sunset These o b s e I v a t l o n s are o b v i o u s l y n o t a c c o u n t a b l e on the basis of t h e a s s u m p t i o n s m a d e for the e x p l a n a t i o n of t h e sunrise effect T h e a v e r a g e d u r a t i o n of t h e sunset rise is 65 min N e x t , t h e s u p e r p o s e d epoch m e t h o d of analysis was used I n s u m m e r p a i t m u larly, a well m a r k e d chp is s o m e t i m e s o b s e r v e d n e a r sunset, s o m e t i m e s before a n d sometm~es a f t e r Such a dip n e a r sunset, m s u m m e r , is o b s e r v e d m t h e average a t m o s p h e r i c s a c t i v i t y b y m a n y workers (LvGEON 1947, BUREAU 1929, WATSOX ~VATT 1926. MACKERROW 1960, H_XRWOOD 1958) T h e lowest p o i n t of this dq) was selected as the zero-epoch Of course, o n l y those days were selected on which such a dip could be o b s e r v e d satisfactorily T h e readings of the a c t i v i t y wele n o t e d f r o m the daily c h a r t s for 3 hi on eithel sade of it, a t an i n t e r v a l of 15 m m F o r t y - f o u l good sets of readings were available f r o m which an a v e I a g e c u r v e was d r a u n (Fig 7 a n d T a b l e 2) T h e c u r v e n a t u l a l l y shows a well m a r k e d dip, b u t it also brings o u t one more mgmficant p o i n t T h e fall f r o m the day-slde is v e r y g r a d u a l a n d similar to a cosine v a r a a t m n B u t the rise is linear a n d steep, up to 60 rain, a f t e r the d i p - m i n i m u m a n d t h e n it s u d d e n l y changes the slope to a v e r y low v a l u e which ~s m a i n t a i n e d up to the end I n c i d e n t l y this rise t i m e of 60 min is
32
M ~,V (~HIPLONKABand R N KAICEKAI¢ IST
1730
1830
I,F
1930
.
1958
2030
i.
~
*
• *
. •
eQ ~ %
•
•
•
I,M
• .
I,A
• .o
*
•
',M I,J
$
l,d
.
I,A
•
IN ID ,959
%,o
.. • |
•
•
.
•
I
•
o.. " ,M IA
Id
°
°•
°•5
#
ii /.?:
•
•
°. .
1,5
.
•~
,
•
.
°
IO Flg
6 Scattm dmglmn of tnne of ~tmt oi sunset H~e on 27 kc/s against the (lay
n e a r l y e q u a l to t h e tmle d u r a t i o n w h m h is f o u n d for t h e a v m a g e sunset ~lse, vm 65 m m This m a y indicate the general v a h d l t y of the results of the f o r m e r m e t h o d also I t s h o u l d be noted, however, t h a t the dip m i n i m a o c c u r r e d before the g r o u n d sunset on t w e n t y - o n e oeeasmns a n d after it on t h i r t y - o n e occasions Also t h e m a x i m u m d e p a r t u r e f r o m the sunset line is a b o u t 30 min I t was seen t h a t the fall of the a v e r a g e c u r v e is mmflar to "cos (t)" v a r i a t i o n a n d so t h e c u r v e of "cos (t)" was superposed, w i t h suitable scales, on the fMhng side of t h e dip (the p o i n t s m a r k e d - x - x - in Fig 7), b u t the zero ot t h e "cos (t)" was t a k e n a t the p o i n t where t h e e x t r a p o l a t e d fM1, cuts t h e plus b0 rain o r d i n a t e Thts p o i n t was t a k e n because it was t h o u g h t t h a t this p o i n t is the real end of the c u r v e as m d m a t e d b y t h e kink in the n s m g side of the dip I t can be seen t h a t t h e eommdenee is v e r y e x a c t F u t h e r m o r e ff the zero of "cos (t)" is t a k e n to comrade w i t h t h e p o i n t of m i n i m u m of the dip (range of " t " m a d e to covet 3 hr
The summe and sunset eft(et~ on the lex el of atmosphelwb actLvJty
33
Table 2 Average dlff.rentlal amplitudes for 3 hr before and after the n m m n u m (epoch) at %nn~et Time from el)od~ (ram)
Amphtude* (ram.)
--180 165 150
!3 9 14 3 14 2
--135 120 - 105
13 8 13 6 13 2
q0
11 8
- 75
10 4
(d)
8 7
--45 --30 --15
69 4q 24
degree
80
04
15 30 45
37 76 10 7
60 75 90
14 4 15 4 16 6
105 120 135
16 5 16 5 17 2
150 1()5 180
17 9 18 5 18 8
~0
C
90
Q~e~ /~
-IC
,
-180
0
5C
0
- 120
--
-6q
3
•
0
t()
120
180
Mr'
F i g 7 Average sunset-dq) vamatmn on 27 ke/.~ (- - ) and cos (t) v a n a t m n ( t - t - c ) auperpo~ed on c a d l othel
* One m m is approxlmatel 3 equal to 12 5 / , V / m / 1 ke/~ b a n d ~ l d t h c o r r e s p o n d i n g l y ) t h e n t h e c o i n c i d e n c e is g o o d o n l y f o r "t" g r e a t e r t h a n a b o u t 30 °, b u t p o i n t s f o r " t ' l e s s t h a n 30 ° h e a l i t t l e a b o v e c u r v e o f t h e f a l l The explanahon of these obselved facts about the dip, paitlcularly that of " c o s ( t ) " v a r i a t i o n , d o e s n o t a p p e a r t o b e r u m p l e L t ' G E O ~ ' S (1947) e x p l a n a t m n t h a t t h e d i p IS p a l t l y d u e t o t h e v a r l a t a o n o f t h u n d e r s t o r m a c t i v i t y a n d p a l t l y to the D-layer absorption seems to be vahd to a certain extent The kink of the nsmg pair may be due to the D-1wer ceasing to absorb T h e e x p l a n a t i o n o f t h e s u n s e t d~p g i v e n b y JOUAUST ( ] 9 4 6 ) d e p e n d s u p o n t h e v a r i a t i o n o f t h e p s e u d o - B r e w s t e r a n g l e o f t h e a o n o s p h e r e d u e t o c h a n g e s in l O n l s a t l o n
34
M W CItIPLONKAR and g
N KAI~EKAR
at of on is
the time of sunset This would suggest that the variation on both ides the minimum must be smooth However, the kink in Fig 7 is difficult to explam this hypothesis unless some other phenomenon llke a diffeient reflecting layel assumed to be connected with the mlmmum Belie concluding this discussion it would be wmthwhlle mentioning one mote point regarding the phenomenon oi a dip nl the level of V L F mgna]s observed at sunl]se HAI~GREAYES (1962) h a s e x p l a i n e d t h i s o n t h e b a s i s o f a t e m p o r a i y enhancement of ionisation reaching a hlghei value than the eqmhbnum one at the ionosphenc sunrise In the D~-layer H e m e n t i o n s t h a t a n e x a m i n a t i o n ot 1,9 6 k c / s t r a n s m i s s i o n s r e c o r d e d a t i a n g e s o f 378 a n d 528 k i n b y t h e R a d i o R e sealch Station. Slough, has levealed a temporary leductlon of leflection height at s u n l ] s e A s i m i l a r e f f e c t is a l s o n o t e d i n t h e a t m o s p h e l i c s actl~ ] t y o n 27 k c / s b o t h a t s u m m e a n d s u n s e t i n a f e w o f t h e m o n t h l y c u i v e s ~ e p o ~ t e d b y B V e E A U (1929) ~EFERENCES A]'I~LETON E V and NAIS~ITtt R ]~AIN W C BmaAL S S BI~ACEWELL R :N BI~ACE~ELL 1% N and BAIN W C BROWN S B and PETRIE W BI/REAU iq
CI-IIPLONKAI%~¢[ %V CHIPLONKA~ M W , and MA~WADI P ELLISO~ M A E~LiSON M A GAICDNEI% F F and 1LIARGREAVE%J ]~ HAI~WOOD J JOUA~rST R
and KAttEKAtt R N KA~EKA~ R N R
:PAWSEY J L
1935 1953 1955 1952 1952 1954 1929 1962 1962
_Proc Roy Soc A150, 685 J Atmosph Te~ l'hys 8, 141 J Atmosph Ter~ 1)hys 6, 160 J Atmosph TeTr Phys 2, 226 J Atmosph Terr l't~y~ 2, 216 Canad J Pl~ys 82, 90 C R Acad Sc~ , ])a~zs December I~d,an J Met (;eot)hy~ 18, ,July J Atmosph Terr 1)l~ys 24, 9
1953 1955 1953 1962 1958 1946
J Atmosph Tear Phy~ 4, 226 U g S I I n f m m a t l o n Bulletin No 92 J Atmosph Tett Phys 3, 321 J Atmosph Terr Phys 24, 1 lboc lust Elect Enqts 105B, 293 L'Ionosphere, pp 179-217, Pam~ (cited b y B~ace~ ell and Barn) Tnage a p a r t de :tnnule~ de la stahun ~et~trale Sutsse de meteoroloff~qu¢ C R Acad Set I'ar~s 188, 1690 J Gcopt~ls Res 65, 1911 J Atmo~t,t~ Tear l'hy,~ 4, 141 .Ph I) t]~cst~ (1 Eeole pol 3 teehmque Fedcrale, Zumeh) J N( ~ Industt Res 17A, 262 J (¢eophys Res 65, 1939 J Geophys Res 57, 487 E x p ~VHelebs & \~ nele~s Engr , 8, 234 J Geophys Rcs 54, 277 l l e p o t t S R I p r o j ( c t No 3171 Stanfold 1%eseareh Institute, Cahfornm
LuGEO~ J
1947
h~CKEm~OW C A MIT~A A P and JONES R E RIEKE~ J
1929 1960 1953 1960
SACHDEV D K WAIT J ]% WATTS J M ~rATSO~ ~VATT 1% A WELLS H ~V WI:[ITSON ~,~ L
1958 1960 1952 1926 1949 1961