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Polarization of radio waves reflected from the ionosphere
Research notes A m a l g a m a t e d Wireless Ltd., Australasia, 1941. [3] BATES, D. R. and MAsssY, H. S. W.; Phil. Trans. Roy. Soc. A 1943 239 269. [4] BIONDI, M. A.; Phys. Rev. 1951 84 1072. [5] COWLING, T. G.; Proc. Roy. Soc. A 1945 183 453. [6] MAssEY, H. S. W.; Negative Ions (2nd edition). Cambridge University Press, 1950. BATES, D. R. a n d SEATON, M. S., Prec. Phys. Soc. B 1950 63 129.
Quee.~ds University, Bel/ast. University College, London.
D. l~. BATES. H . S . W . MASSEY, ~'. R. S.
Polarization of radio waves reflected from the ionosphere M e a s u r e m e n t s of t h e l i m i t i n g p o l a r i z a t i o n of r a d i o w a v e s r e f l e c t e d fronl t h e i o n o s p h e r e a t v e r t i c a l i n c i d e n c e were m a d e a t t h e N o r w e g i a n D e f e n c e R e s e a r c h E s t a b l i s h m e n t a t Kjeller n e a r Oslo (60 ° N, 11 ° E ) d u r i n g N o v e m b e r 1950 a n d a t t h e A u r o r a l O b s e r v a t o r y in T r o m s o (70 ° N, 19 ° E) d u r i n g S e p t e m b e r a n d O c t o b e r 1951.
a
b
a
b
Fig. 1. Left : a shows the ground-ray with height marks each 50 kin; b the ground-ray is gated and dmplayed on a second CRT. Right: a shows Fz-echoes; b the x-component is gated and displayed oil a second CRT. T h e e x p e r i m e n t a l s y s t e m for t h e m e a s u r e m e n t s was t h e s t a n d a r d s y s t e m u s i n g crossed loops, s e p a r a t e r e c e i v e r c h a n n e l s w i t h a c o m m o n oscillator a n d a n oscilloscopic r e p r e s e n t a t i o n of t h e ellipse of p o l a r i z a t i o n . T h e following r e s u l t s were o b t a i n e d : 1. T h e sense of r o t a t i o n for t h e t h i r d m a g n e t o - i o n i c c o m p o n e n t ( t h e z - c o m p o n e n t ) was d e t e r m i n e d . T h e z - c o m p o n e n t was f o u n d to b e p o l a r i z e d in t h e s a m e w a y as t h e o r d i n a r y comp o n e n t . T h i s r e s u l t h a s also r e c e n t l y b e e n o b t a i n e d b y HOGARTH ( N a t u r e , L o n d . 1951 161 597). 2. A t Kjeller, a b s o r p t i o n m e a s u r e m e n t s were c a r r i e d o u t b y F. LIED a t t h e s a m e t i m e as t h e p o l a r i z a t i o n m e a s u r e m e n t s were m a d e . C o r r e l a t i o n w a s f o u n d b e t w e e n t h e m e a n v a l u e s of t h e a b s o r p t i o n i n d e x D a n d t h e axis r a t i o e of t h e ellipse of p o l a r i z a t i o n . T h e c o r r e l a t i o n is s h o w n in Fig. 2. T h e o b s e r v a t i o n s were m a d e a t a b o u t 12 h M.E.T. e v e r y d a y o n a f r e q u e n c y of 3.6 Mc/s. On t h i s f r e q u e n c y o n l y t h e o r d i n a r y m a g n e t o - i o n i c c o m p o n e n t was p r e s e n t . T h i s r e s u l t seems t o b e in d i s c r e p a n c y w i t h t h e m a g n e t o - i o n i c t h e o r y . A c c o r d i n g to t h e r a y t h e o r y a n i n c r e a s e in t h e a b s o r p t i o n s h o u l d m a k e t h e ellipse of p o l a r i z a t i o n m o r e circular t h a n eccentric. T h e effect m a y b e e x p l a i n e d as d u e t o a r e s p l i t t i n g of t h e r e f l e c t e d o r d i n a r y w a v e i n t o b o t h a n o r d i n a r y a n d a n e x t r a o r d i n a r y w a v e d u r i n g t h e p a s s a g e t h r o u g h t h e lower p a r t of t h e i o n o s p h e r e . 3. D u r i n g p o l a r m a g n e t i c s t o r m s a n d a u r o r a l d i s p l a y s in T r o m s o t h e ellipse of p o l a r i z a t i o n was f o u n d t o u n d e r g o m a r k e d v a r i a t i o n s . I n Fig. 3 m e a n v a l u e s of t h e axis r a t i o e of t h e ellipse of p o l a r i z a t i o n are p l o t t e d t o g e t h e r w i t h a r e c o r d of t h e h o r i z o n t a l e a r t h m a g n e t i c force on a m a g n e t i c a l l y quiet d a y a n d a m a g n e t i c a l l y disturbed day. On 23rd O c t o b e r 1951, a t a b o u t 16 h M.E.T., a p o l a r m a g n e t i c s t o r m a p p e a r e d . A t t h e s a m e t i m e , in less t h a n o n e h o u r , t h e axis r a t i o s c h a n g e d f r o m 0-92 t o 0-68. F u r t h e r s t u d i e s are r e q u i r e d b e f o r e t h e o b s e r v e d effect c a n b e fully e x p l a i n e d , b u t t h e effect m a y well b e d u e to a m e c h a n i s m similar to t h e o n e p r o p o s e d in (2). I t is well k n o w n t h a t , d u r i n g p o l a r m a g n e t i c s t o r m s , t h e c o n c e n t r a t i o n of e l e c t r o n s in t h e lower p a r t s of t h e i o n o s p h e r e
254
Research notes is i n c r e a s e d . D u r i n g s u c h c o n d i t i o n s t h e o c c u r r e n c e of d i s c o n t i n u i t i e s , a n d t h e r e b y t h e condit i o n s for a r e s p l i t t i n g of t h e o r d i n a r y w a v e i n t o a n o r d i n a r y a n d a n e x t r a o r d i n a r y w a v e , m a y be e x p e c t e d . 000
--
-800
700-- ~ 600
OO
-700
-
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500-
SERVED
~ ,
4 O0 -
MEAN
VALUES O F
THE
ABSO,qPTIONINDEX O.
-500
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- 400
300-
- 300
0.8 -
ol
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- 0.8
0.9 -I. C
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l
1.0
l
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1
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I
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1
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I
I
fS DArE
I
I
I
|
I
20
I
I
I
I
I
25
30 th.
NOVEMBER /950.
Fig. 2. Observed m e a n valugs of the absorption index D and the axis ratio of the ellipse of polarization. K is a symbol for s t o r m conditions. The observations were m a d e at Kjeller.
HORIZONTAL MAGN~'rlC FORCE.
I HORI2~VTAL MAGNETIC FORCE1
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I
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0.5 125
0.6 14
16
I0
20 h
12h
OCTOBE# 23rd.
14 16 18 OCrOBE# 2Sth.
20 h
blEE Fig. 3. Observed m e a n values of the axis ratio ~ of the ellipse of polarization for an earthmagnetically quiet and a disturbed day. The observatio~:~ were m a d e at Tromsz.
T h e a u t h o r w o u l d like to e x p r e s s h i s i n d e b t e d n e s s to Dr. L. HARAI~'G, u n d e r w h o s e s u p e r v i s i o r. t h e p r e s e n t w o r k w a s done. H e also w o u l d like to t h a n k Mr. F. LIED for h i s m o s t i n s p i r i n g help. .7~orwegian De/e~lce R e s e a r c h E s t a b l i s h m e n t ,
K j e l l e r , Oslo.
255
BJ~RN LAND:~IARK.
Quee.~ds University, Bel/ast. University College, London.
D. l~. BATES. H . S . W . MASSEY, ~'. R. S.
Polarization of radio waves reflected from the ionosphere M e a s u r e m e n t s of t h e l i m i t i n g p o l a r i z a t i o n of r a d i o w a v e s r e f l e c t e d fronl t h e i o n o s p h e r e a t v e r t i c a l i n c i d e n c e were m a d e a t t h e N o r w e g i a n D e f e n c e R e s e a r c h E s t a b l i s h m e n t a t Kjeller n e a r Oslo (60 ° N, 11 ° E ) d u r i n g N o v e m b e r 1950 a n d a t t h e A u r o r a l O b s e r v a t o r y in T r o m s o (70 ° N, 19 ° E) d u r i n g S e p t e m b e r a n d O c t o b e r 1951.
a
b
a
b
Fig. 1. Left : a shows the ground-ray with height marks each 50 kin; b the ground-ray is gated and dmplayed on a second CRT. Right: a shows Fz-echoes; b the x-component is gated and displayed oil a second CRT. T h e e x p e r i m e n t a l s y s t e m for t h e m e a s u r e m e n t s was t h e s t a n d a r d s y s t e m u s i n g crossed loops, s e p a r a t e r e c e i v e r c h a n n e l s w i t h a c o m m o n oscillator a n d a n oscilloscopic r e p r e s e n t a t i o n of t h e ellipse of p o l a r i z a t i o n . T h e following r e s u l t s were o b t a i n e d : 1. T h e sense of r o t a t i o n for t h e t h i r d m a g n e t o - i o n i c c o m p o n e n t ( t h e z - c o m p o n e n t ) was d e t e r m i n e d . T h e z - c o m p o n e n t was f o u n d to b e p o l a r i z e d in t h e s a m e w a y as t h e o r d i n a r y comp o n e n t . T h i s r e s u l t h a s also r e c e n t l y b e e n o b t a i n e d b y HOGARTH ( N a t u r e , L o n d . 1951 161 597). 2. A t Kjeller, a b s o r p t i o n m e a s u r e m e n t s were c a r r i e d o u t b y F. LIED a t t h e s a m e t i m e as t h e p o l a r i z a t i o n m e a s u r e m e n t s were m a d e . C o r r e l a t i o n w a s f o u n d b e t w e e n t h e m e a n v a l u e s of t h e a b s o r p t i o n i n d e x D a n d t h e axis r a t i o e of t h e ellipse of p o l a r i z a t i o n . T h e c o r r e l a t i o n is s h o w n in Fig. 2. T h e o b s e r v a t i o n s were m a d e a t a b o u t 12 h M.E.T. e v e r y d a y o n a f r e q u e n c y of 3.6 Mc/s. On t h i s f r e q u e n c y o n l y t h e o r d i n a r y m a g n e t o - i o n i c c o m p o n e n t was p r e s e n t . T h i s r e s u l t seems t o b e in d i s c r e p a n c y w i t h t h e m a g n e t o - i o n i c t h e o r y . A c c o r d i n g to t h e r a y t h e o r y a n i n c r e a s e in t h e a b s o r p t i o n s h o u l d m a k e t h e ellipse of p o l a r i z a t i o n m o r e circular t h a n eccentric. T h e effect m a y b e e x p l a i n e d as d u e t o a r e s p l i t t i n g of t h e r e f l e c t e d o r d i n a r y w a v e i n t o b o t h a n o r d i n a r y a n d a n e x t r a o r d i n a r y w a v e d u r i n g t h e p a s s a g e t h r o u g h t h e lower p a r t of t h e i o n o s p h e r e . 3. D u r i n g p o l a r m a g n e t i c s t o r m s a n d a u r o r a l d i s p l a y s in T r o m s o t h e ellipse of p o l a r i z a t i o n was f o u n d t o u n d e r g o m a r k e d v a r i a t i o n s . I n Fig. 3 m e a n v a l u e s of t h e axis r a t i o e of t h e ellipse of p o l a r i z a t i o n are p l o t t e d t o g e t h e r w i t h a r e c o r d of t h e h o r i z o n t a l e a r t h m a g n e t i c force on a m a g n e t i c a l l y quiet d a y a n d a m a g n e t i c a l l y disturbed day. On 23rd O c t o b e r 1951, a t a b o u t 16 h M.E.T., a p o l a r m a g n e t i c s t o r m a p p e a r e d . A t t h e s a m e t i m e , in less t h a n o n e h o u r , t h e axis r a t i o s c h a n g e d f r o m 0-92 t o 0-68. F u r t h e r s t u d i e s are r e q u i r e d b e f o r e t h e o b s e r v e d effect c a n b e fully e x p l a i n e d , b u t t h e effect m a y well b e d u e to a m e c h a n i s m similar to t h e o n e p r o p o s e d in (2). I t is well k n o w n t h a t , d u r i n g p o l a r m a g n e t i c s t o r m s , t h e c o n c e n t r a t i o n of e l e c t r o n s in t h e lower p a r t s of t h e i o n o s p h e r e
254
Research notes is i n c r e a s e d . D u r i n g s u c h c o n d i t i o n s t h e o c c u r r e n c e of d i s c o n t i n u i t i e s , a n d t h e r e b y t h e condit i o n s for a r e s p l i t t i n g of t h e o r d i n a r y w a v e i n t o a n o r d i n a r y a n d a n e x t r a o r d i n a r y w a v e , m a y be e x p e c t e d . 000
--
-800
700-- ~ 600
OO
-700
-
- 600
500-
SERVED
~ ,
4 O0 -
MEAN
VALUES O F
THE
ABSO,qPTIONINDEX O.
-500
~K
- 400
300-
- 300
0.8 -
ol
"~MEAN VALUES OF THE AXIS
- 0.8
0.9 -I. C
-0.9
l
1.0
l
t
1
S th
I
I
=
I
I
I
]
I0
1
I
I
I
fS DArE
I
I
I
|
I
20
I
I
I
I
I
25
30 th.
NOVEMBER /950.
Fig. 2. Observed m e a n valugs of the absorption index D and the axis ratio of the ellipse of polarization. K is a symbol for s t o r m conditions. The observations were m a d e at Kjeller.
HORIZONTAL MAGN~'rlC FORCE.
I HORI2~VTAL MAGNETIC FORCE1
I~
,
i
•
•
~
I
I
i
I
0.9
,g
0.8
I l
0.8
'
017
-0.7
0.5 125
0.6 14
16
I0
20 h
12h
OCTOBE# 23rd.
14 16 18 OCrOBE# 2Sth.
20 h
blEE Fig. 3. Observed m e a n values of the axis ratio ~ of the ellipse of polarization for an earthmagnetically quiet and a disturbed day. The observatio~:~ were m a d e at Tromsz.
T h e a u t h o r w o u l d like to e x p r e s s h i s i n d e b t e d n e s s to Dr. L. HARAI~'G, u n d e r w h o s e s u p e r v i s i o r. t h e p r e s e n t w o r k w a s done. H e also w o u l d like to t h a n k Mr. F. LIED for h i s m o s t i n s p i r i n g help. .7~orwegian De/e~lce R e s e a r c h E s t a b l i s h m e n t ,
K j e l l e r , Oslo.
255
BJ~RN LAND:~IARK.