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Hydrogen lines in auroral glow
J ournal of Atmospheric and Terrestrial Physics, ] 9fi2. Vol. 24, pp. 203 to 209. Pergamon Press lad. Printed in Nol'thern Ircbmd
Hydrogen lines in auroral glow A. O~IHOLT The N o r w e g i a n I n s t i t u t e of Cosmic P h y s i c s a n d The I n s t i t u t e of T h e o r e t i c a l A s t r o p h y s i . ~ . U n i v e r s i t y of Oslo, B l i n d e r n . N o r w a y all(t
W. STOFFaEGEX and H. DERBLO~, U p p s a l a I o n o s p h e r i c O b s e r v a t o r y , R e s e a r c h I n s t i t u t e of N a t i o n a l l)cf,~Hce, Swo(hm ( Receiverl 7 October 1961 )
Abstract -The p a p e r r e p o r t s s o m e o b s e r v a t i o n s of a u r o r a ove r n o r t h e r n S c a n d i n a v i a w i t h a t~ew p h o t o e.lcctrie s p e c t r o g r a p h . The a u r o r a e c o n s i s t e d of a w e a k b u t p e r s i s t e n t g l o w s h o w i n g a n u n u s u a l s t r o n g H ~ line, a n d of d i s t i n c t , b r i g h t e r forms s h o w i n g no t r a c e of H~. B e t w e e n t h e b r i g h t e r f o r m s a nd t h e gl ow a d a r k a r e a occurred. T h e o b s e r v a t i o n s are d i s c u s s e d bricfly a nd it ix f t . m d possible t h a t t he glc~ws wet,' ~xeited purely by proton impact.
[N THIS PAPER we shall report obserw~tions of a weak auroral glow over Trolnsii. Norway, in the auroral zone, on the night of 9/10 F e b r u a r y 1961, and one over Kiruna, Sweden, near the auroral zone, in the evening of 11 March 1961. The observations were made with new fast scanning photoelectric spectrographs, and the glow showed such a strong H~. line t h a t it is likely t h a t it was excited purely by incident protons. The instruments were two identical spectrographs (SP3) constructed by the authors in cooperation with Professor L. HARA~'G, and built by the Research [nstitute of National Defence, Sweden. It can either p h o t o g r a p h the spectrum or record it photoelectrically. The first order photographic spectrum has a dispersion of a b o u t 90 A/mm, using a light power of 0-71. When photoelectric recording is used, the grating is t u r n e d such t h a t the light is reitected back through the collimator ( F -- 1:5) lens and forms a spectrum on an exit slit. The slits are 4 em long and the resolution is such t h a t the i n s t r u m e n t can resolve lines which are 1 A apart. The scanning system is similar to t h a t used by HV>-TEX (1953), and the wavelength range scanned by the i n s t r u m e n t m a y be varied from 60 to 5000 a~ in the first order. The scanning time is 15, 60 or 240 sec. The recording system is based on photon counting, using a r a t e m e t e r and a recording mA-meter. A full description of the in s tr u men t will be given elsewhere later. Typical records are shown in Figs. 1 and 2. During the night 9/10 F e b r u a r y 1961, the Troms6 spectrometer scanned from about 6350 A to 6650 A every minute. To get enough light the slits were opened to a width of 0.4 ram, equivalent to 7 A. For a short period the recording time per spectrum was e xt e nde d to 4 rain to obtain higher accuracy in the H~.-profile From 1S00 hours M.E.T., when the observations started, to about 2300 hours the visible aurora consisted of a faint glow covering the n o r t h e r n half of the sky, and a weak arc at the horizon in the north. The glow was barely visible to the eye, and seemed to have a fairly sharp southern borderline in the east-west direction. passing close to zenith. The spectrum shown in Fig. 1 is typical for this gloxv. The intensity of the H~-line increased slowly from 1,q00 to 2030 hours. B e t w e e , 2O3
204
A . OMHOLT
2030 and 2100 hours it reached its maximum, which was more t h a n twice the intensity at 1800 hours. F r o m 2100 to 2200 hours it decreased again to its original value, and then remained constant until about 2310 hours. The red IOI] line at 6364 A showed a similar behaviour, and the total intensities of the two lines were roughly equal. During the observation period spectra were taken in various directions. The glow was fairly homogeneous, but the [OI] line was stronger in the north. above the arc, and the arc itself showed the First Positive N 2 bands in the red, but no H~-line. These N.~ bands were not of recordable intensity in the glow.
Ha
[oil
Fig. 1. S p e c t r u m of auroral glow over Troms6, showing Hc~ and the 6364 lOT ] line.
F r o m 2310 to 0100 hours active, distinct auroral forms were present in the northern half of the sky and in the zenith. These, and the weak, p a t c h y glow in between them, showed no Ha-line, whereas a persistent broad band with glow-like appearance south of the active zone showed the same spectral characteristics as the preceding glow. From 0100 to 0130 hours the picture was again much the same as before 2310 hours, whereas at 0130 hours a new active period began, this time with long rays and pulsating aurora. Now the situation became quite complicated and confusing, and similar to situations studied earlier by means of a filter photometer (OMttOLT, 1959). The Ha-line was undoubtedly present in the quiet background glow, but did not a n y more dominate the red part of the spectrum. The magnetic records show a positive bay in the H-component around 1645 hours M.E.T., a slight depression later, and a small negative bay commencing at about midnight and lasting until about 0400 hours. The glow was not visible on the all-sky camera pictures. A similar set of observations were obtained at K i r u n a in Sweden on 1 l March 1961. A few of the original records with scanning ranges 800 and 100 A respectively are shown in Fig. 2. The slit width was 0.5 mm (8 _~) and the spectrograph was
Hydrogen lines in auroral glow
KIRUNA 11 MARCH
205
1961 OI
7000
6500 I
100
£
MET]
20.24 ~ 20.20~ " - , ~
~
20.18 20.13 20,11
20.03
--~
6550
6500 ~,
Fig. 2. Speet.raof aurora in zenith over Kiruna, showing Hc¢and the First Positive N~bands. directed t o w a r d s z e n i t h all the time. T h e r e l e v a n t o b s e r v a t i o n a l results are p l o t t e d in Fig. 3. Because of b a d visibility a t K i r u n a Ml-sky c a m e r a p h o t o g r a p h s were o n l y p a r t l y usable, b u t b e t t e r ascafilms f r o m Lyeksele, 370 k m s o u t h of K i r u n a , s h o w e d the glow clearly a n d could be used for p l o t t i n g its n o r t h - s o u t h e x t e n t . A h e i g h t of 100 k m was a s s u m e d for this purpose. A t a b o u t 1900-1930 h o u r s
2(16
A. ()MHOLT
I KIRUNA 11 MARCH
1961
T
H - INTENSITY
7
ioo
j5 .
.
.
.
.
.
.
.
.
.
.
.
L AURORA-PLOT,
N Km F' 300-
100 Km HEIGTH
100 0 " KIRUNA--~
100
G,OW i ,II III I '~ il
2O0
I ~1 ~"iI~' Y/Ji'!Jl'~
25C S
SPECTRUM
INTENSITY, ZENITH [
/\
1 PG N2
i
I ,d / .I
i
20 00
2100 MET
Fig. 3. Geomagnetic data and latitudM occurrence of" the aurora wit,h time at Kiruna. 11 March 1961 M.E.T. no aurora was visible but a very faint glow which covered the northern part o f t h e s k y u p t o z e n i t h , a n d a s t r o n g H a - l i n e w a s o b s e r v e d . A t 2014 h o u r s a s u d d e n positive increase of the geomagnetic H-intensity was recorded simultaneously with
:Hydrogen lines in auroral glow
207
the appearance of an arc near zenith. During the period from 2014 to 2022 hours the auroral glow moved to the south to about 100-200 km south of K i r u n a and became brighter. During these S min the glow became much weaker in zenith at K i r u n a and only during this period a bright auroral arc was visible. Then the at(disappeared, but a faint arc reappeared again somewhat nort h of K i r u n a from 2045 to 2105 hours. As in the Troms5 aurora, the Hc~ emission was d e a r l y associated with the glow. and not detectable in the ares, which showed strong First Positiw~ N., Bands.
I
I
KIRUNA ~, ~1 MARCH1961
/~7~, x
/~// _/,
} I
\
"-.b ,
,--.."
TROMS
*20
0
-20
-40A
~,
Fig, 4. He< profiles: (a) glow over TromsS, 60 ° angle between the line of sight and the magnetic lines of fm'ee. (b) and (e) glow over Kiruna, average zenith profiles 2116-2124 hours M.E,T. (b) and 1953 1958 hours M.E.T. (e).
Both in Troms6 and K i r u n a the " h y d r o g e n glow" seemed to flee from the area where the brighter forms appeared (of. Fig. 3). Between the bright ares and the glow there was a dark area with no aurora, and this dark area m ay he as wide as 100 km in the n o r t h - s o u t h direction. This phenomenon seems to be quite common. judged from the Ml-sky photographs studied at Uppsala Ionospherie Observatory. The profiles of the H~-lines measured are similar to those observed by other workers earlier. Three profiles are shown in Fig. 4, one from the Troms5 records (a) and two h'om K i r u n a (b and c). All the profiles shown are averages of several successive records. The difference between the two profiles from K i r u n a (b and c) is remarkable. T he y are bot h zenith (not magnetie zenith) profiles, hut the halfwidth of t h a t from the early pa r t of the aurora (c) is less t han t h a t from the late,' part of the aurora (b). The hydrogen emission observed here is not unique, being u n d o u b t e d l y the same as t h a t observed by ROMICK and ELVEY (1958), GALeERI>r (195q), BLESS et al. (1960) and REES et al. (1961). T h e y have, however, all used conventional spectrographs with ihirly long exposure times, whereas this new i n s t r u m e n t permits a more detailed analysis in time, space and wavelength. I t occurs to us t h a t there were
208
A. OMI£OLT
two distinctly different types of aurora present these nights, an extensive and fairly homogeneous "hydrogen glow", and distinct auroral forms further north, the latter being presumably excited by electrons. No absolute calibration of the sensitivity of the spectrographs were available, but the intensities of the glow were estimated to correspond to brightness coefficient I or to be slightly higher. This agrees fairly well with the critical frequency of the associated E,-layer, which in Troms5 was measured by the ionospheric recorder and varied between 2.5 and 4"0 Mc/s (cf. OMKOLT, 1955). The intensity of the H~-line in the glow was unusually strong, and roughly equal to or slightly greater than t h a t of the [OIl line at 6364 A. I t must have been an order of magnitude greater than t h a t of the neighbouring First Positive N 2 bands, which were not detectable. No other lines or bands were measured, but using generally accepted intensity relations in the auroral spectrum, we find t h a t the intensity ratio betwee|l the H~-line and the green [OIl line at 5577 ~: caunot have been less t h a n o,1 (of. HUNTEN, 1955; O~IIIOLT, 1957; BATES, 1960), probably rather of the order 0.5. 100 keV protons yield approximately 150 emitted quanta in the First Negative N., -~ band as well as of the green line (cf. ()~'I~OLT, 1959; BATES, 1960), and about 50 H~. quanta (CHAMBERLAIN,1961). This means t h a t the observed glow could well have been excited entirely by protons with average energy around ]00 keV. The current ideas about the interpretation of the hydrogen line profile (cf. CHA:m~m~I,A~:X'.1961) would perhaps suggest a somewhat lower average proton impact energy, but the uncertainties in the energy distribution are such t h a t the average energy cannot be established from the profiles with any accuracy. This relative strength of the hydrogen lines has never been observed earlier in TromsS, in spite of the extensive spectrographic measurements (cf. \qCGARD et
and Mr. REIDULV LARSEN of the Auroral Observatory in Troms6 for their kind
Hydrogen
lines in aurora1 glow
30!)
assistance in preparing the electronic apparatus, and to Mrs. HELEN Aasm The Norwegian part of the research reported in for processing his observations. this paper was supported by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, U.S. Air Force, under contract AF 61 (051)-252 through the European Office. REFERENCES 1960
Physics of the CTpper Atrnosphrre (Ed. by J. A. Ratcliffe), ('hap.7.
ULESY K.C.,GARTLEIN C. W. and SPRAGUE G. ('HAMBERLAIN J. 1%:.
1960 1961
(:.~LPERIN ($.I. HUNTEN D.M. HUNTEN D.M. OMHOLT A. OMHOLT A. OMHOLTA. REES M.H.,BELoNA.E.~~~Ro~MIcK ROMICK G.J.~~~ELvEYC.T. \r~~~~~)I>., BERGER S. and KUNDAL
1959 1953 1955 1965 1957 19.59 1961 1958 1968
J. Geophys. Res. 65, 565. Physics of the Aurora and Airglow. Academic Press, New York. Planet. Space Sci. 1, 57. Canad. J. Phys. 31,081. ,I. Atmosph. Terr. l’hys. 7, 141. J. -4tmosph. Terr. Phys. 7, 73. J. Atmosph. Terr. Phys. 10, 320. Geofys. Publ. 20, h70. 11. Planet. Space Sci. 5, X7. .J. Atmosph. Terr. l’hys. 12, 283. Geofys. Publ. 20, No. 9.
HATES
1). Ii.
Academic Press,Xew York.
G.J. A.
Hydrogen lines in auroral glow A. O~IHOLT The N o r w e g i a n I n s t i t u t e of Cosmic P h y s i c s a n d The I n s t i t u t e of T h e o r e t i c a l A s t r o p h y s i . ~ . U n i v e r s i t y of Oslo, B l i n d e r n . N o r w a y all(t
W. STOFFaEGEX and H. DERBLO~, U p p s a l a I o n o s p h e r i c O b s e r v a t o r y , R e s e a r c h I n s t i t u t e of N a t i o n a l l)cf,~Hce, Swo(hm ( Receiverl 7 October 1961 )
Abstract -The p a p e r r e p o r t s s o m e o b s e r v a t i o n s of a u r o r a ove r n o r t h e r n S c a n d i n a v i a w i t h a t~ew p h o t o e.lcctrie s p e c t r o g r a p h . The a u r o r a e c o n s i s t e d of a w e a k b u t p e r s i s t e n t g l o w s h o w i n g a n u n u s u a l s t r o n g H ~ line, a n d of d i s t i n c t , b r i g h t e r forms s h o w i n g no t r a c e of H~. B e t w e e n t h e b r i g h t e r f o r m s a nd t h e gl ow a d a r k a r e a occurred. T h e o b s e r v a t i o n s are d i s c u s s e d bricfly a nd it ix f t . m d possible t h a t t he glc~ws wet,' ~xeited purely by proton impact.
[N THIS PAPER we shall report obserw~tions of a weak auroral glow over Trolnsii. Norway, in the auroral zone, on the night of 9/10 F e b r u a r y 1961, and one over Kiruna, Sweden, near the auroral zone, in the evening of 11 March 1961. The observations were made with new fast scanning photoelectric spectrographs, and the glow showed such a strong H~. line t h a t it is likely t h a t it was excited purely by incident protons. The instruments were two identical spectrographs (SP3) constructed by the authors in cooperation with Professor L. HARA~'G, and built by the Research [nstitute of National Defence, Sweden. It can either p h o t o g r a p h the spectrum or record it photoelectrically. The first order photographic spectrum has a dispersion of a b o u t 90 A/mm, using a light power of 0-71. When photoelectric recording is used, the grating is t u r n e d such t h a t the light is reitected back through the collimator ( F -- 1:5) lens and forms a spectrum on an exit slit. The slits are 4 em long and the resolution is such t h a t the i n s t r u m e n t can resolve lines which are 1 A apart. The scanning system is similar to t h a t used by HV>-TEX (1953), and the wavelength range scanned by the i n s t r u m e n t m a y be varied from 60 to 5000 a~ in the first order. The scanning time is 15, 60 or 240 sec. The recording system is based on photon counting, using a r a t e m e t e r and a recording mA-meter. A full description of the in s tr u men t will be given elsewhere later. Typical records are shown in Figs. 1 and 2. During the night 9/10 F e b r u a r y 1961, the Troms6 spectrometer scanned from about 6350 A to 6650 A every minute. To get enough light the slits were opened to a width of 0.4 ram, equivalent to 7 A. For a short period the recording time per spectrum was e xt e nde d to 4 rain to obtain higher accuracy in the H~.-profile From 1S00 hours M.E.T., when the observations started, to about 2300 hours the visible aurora consisted of a faint glow covering the n o r t h e r n half of the sky, and a weak arc at the horizon in the north. The glow was barely visible to the eye, and seemed to have a fairly sharp southern borderline in the east-west direction. passing close to zenith. The spectrum shown in Fig. 1 is typical for this gloxv. The intensity of the H~-line increased slowly from 1,q00 to 2030 hours. B e t w e e , 2O3
204
A . OMHOLT
2030 and 2100 hours it reached its maximum, which was more t h a n twice the intensity at 1800 hours. F r o m 2100 to 2200 hours it decreased again to its original value, and then remained constant until about 2310 hours. The red IOI] line at 6364 A showed a similar behaviour, and the total intensities of the two lines were roughly equal. During the observation period spectra were taken in various directions. The glow was fairly homogeneous, but the [OI] line was stronger in the north. above the arc, and the arc itself showed the First Positive N 2 bands in the red, but no H~-line. These N.~ bands were not of recordable intensity in the glow.
Ha
[oil
Fig. 1. S p e c t r u m of auroral glow over Troms6, showing Hc~ and the 6364 lOT ] line.
F r o m 2310 to 0100 hours active, distinct auroral forms were present in the northern half of the sky and in the zenith. These, and the weak, p a t c h y glow in between them, showed no Ha-line, whereas a persistent broad band with glow-like appearance south of the active zone showed the same spectral characteristics as the preceding glow. From 0100 to 0130 hours the picture was again much the same as before 2310 hours, whereas at 0130 hours a new active period began, this time with long rays and pulsating aurora. Now the situation became quite complicated and confusing, and similar to situations studied earlier by means of a filter photometer (OMttOLT, 1959). The Ha-line was undoubtedly present in the quiet background glow, but did not a n y more dominate the red part of the spectrum. The magnetic records show a positive bay in the H-component around 1645 hours M.E.T., a slight depression later, and a small negative bay commencing at about midnight and lasting until about 0400 hours. The glow was not visible on the all-sky camera pictures. A similar set of observations were obtained at K i r u n a in Sweden on 1 l March 1961. A few of the original records with scanning ranges 800 and 100 A respectively are shown in Fig. 2. The slit width was 0.5 mm (8 _~) and the spectrograph was
Hydrogen lines in auroral glow
KIRUNA 11 MARCH
205
1961 OI
7000
6500 I
100
£
MET]
20.24 ~ 20.20~ " - , ~
~
20.18 20.13 20,11
20.03
--~
6550
6500 ~,
Fig. 2. Speet.raof aurora in zenith over Kiruna, showing Hc¢and the First Positive N~bands. directed t o w a r d s z e n i t h all the time. T h e r e l e v a n t o b s e r v a t i o n a l results are p l o t t e d in Fig. 3. Because of b a d visibility a t K i r u n a Ml-sky c a m e r a p h o t o g r a p h s were o n l y p a r t l y usable, b u t b e t t e r ascafilms f r o m Lyeksele, 370 k m s o u t h of K i r u n a , s h o w e d the glow clearly a n d could be used for p l o t t i n g its n o r t h - s o u t h e x t e n t . A h e i g h t of 100 k m was a s s u m e d for this purpose. A t a b o u t 1900-1930 h o u r s
2(16
A. ()MHOLT
I KIRUNA 11 MARCH
1961
T
H - INTENSITY
7
ioo
j5 .
.
.
.
.
.
.
.
.
.
.
.
L AURORA-PLOT,
N Km F' 300-
100 Km HEIGTH
100 0 " KIRUNA--~
100
G,OW i ,II III I '~ il
2O0
I ~1 ~"iI~' Y/Ji'!Jl'~
25C S
SPECTRUM
INTENSITY, ZENITH [
/\
1 PG N2
i
I ,d / .I
i
20 00
2100 MET
Fig. 3. Geomagnetic data and latitudM occurrence of" the aurora wit,h time at Kiruna. 11 March 1961 M.E.T. no aurora was visible but a very faint glow which covered the northern part o f t h e s k y u p t o z e n i t h , a n d a s t r o n g H a - l i n e w a s o b s e r v e d . A t 2014 h o u r s a s u d d e n positive increase of the geomagnetic H-intensity was recorded simultaneously with
:Hydrogen lines in auroral glow
207
the appearance of an arc near zenith. During the period from 2014 to 2022 hours the auroral glow moved to the south to about 100-200 km south of K i r u n a and became brighter. During these S min the glow became much weaker in zenith at K i r u n a and only during this period a bright auroral arc was visible. Then the at(disappeared, but a faint arc reappeared again somewhat nort h of K i r u n a from 2045 to 2105 hours. As in the Troms5 aurora, the Hc~ emission was d e a r l y associated with the glow. and not detectable in the ares, which showed strong First Positiw~ N., Bands.
I
I
KIRUNA ~, ~1 MARCH1961
/~7~, x
/~// _/,
} I
\
"-.b ,
,--.."
TROMS
*20
0
-20
-40A
~,
Fig, 4. He< profiles: (a) glow over TromsS, 60 ° angle between the line of sight and the magnetic lines of fm'ee. (b) and (e) glow over Kiruna, average zenith profiles 2116-2124 hours M.E,T. (b) and 1953 1958 hours M.E.T. (e).
Both in Troms6 and K i r u n a the " h y d r o g e n glow" seemed to flee from the area where the brighter forms appeared (of. Fig. 3). Between the bright ares and the glow there was a dark area with no aurora, and this dark area m ay he as wide as 100 km in the n o r t h - s o u t h direction. This phenomenon seems to be quite common. judged from the Ml-sky photographs studied at Uppsala Ionospherie Observatory. The profiles of the H~-lines measured are similar to those observed by other workers earlier. Three profiles are shown in Fig. 4, one from the Troms5 records (a) and two h'om K i r u n a (b and c). All the profiles shown are averages of several successive records. The difference between the two profiles from K i r u n a (b and c) is remarkable. T he y are bot h zenith (not magnetie zenith) profiles, hut the halfwidth of t h a t from the early pa r t of the aurora (c) is less t han t h a t from the late,' part of the aurora (b). The hydrogen emission observed here is not unique, being u n d o u b t e d l y the same as t h a t observed by ROMICK and ELVEY (1958), GALeERI>r (195q), BLESS et al. (1960) and REES et al. (1961). T h e y have, however, all used conventional spectrographs with ihirly long exposure times, whereas this new i n s t r u m e n t permits a more detailed analysis in time, space and wavelength. I t occurs to us t h a t there were
208
A. OMI£OLT
two distinctly different types of aurora present these nights, an extensive and fairly homogeneous "hydrogen glow", and distinct auroral forms further north, the latter being presumably excited by electrons. No absolute calibration of the sensitivity of the spectrographs were available, but the intensities of the glow were estimated to correspond to brightness coefficient I or to be slightly higher. This agrees fairly well with the critical frequency of the associated E,-layer, which in Troms5 was measured by the ionospheric recorder and varied between 2.5 and 4"0 Mc/s (cf. OMKOLT, 1955). The intensity of the H~-line in the glow was unusually strong, and roughly equal to or slightly greater than t h a t of the [OIl line at 6364 A. I t must have been an order of magnitude greater than t h a t of the neighbouring First Positive N 2 bands, which were not detectable. No other lines or bands were measured, but using generally accepted intensity relations in the auroral spectrum, we find t h a t the intensity ratio betwee|l the H~-line and the green [OIl line at 5577 ~: caunot have been less t h a n o,1 (of. HUNTEN, 1955; O~IIIOLT, 1957; BATES, 1960), probably rather of the order 0.5. 100 keV protons yield approximately 150 emitted quanta in the First Negative N., -~ band as well as of the green line (cf. ()~'I~OLT, 1959; BATES, 1960), and about 50 H~. quanta (CHAMBERLAIN,1961). This means t h a t the observed glow could well have been excited entirely by protons with average energy around ]00 keV. The current ideas about the interpretation of the hydrogen line profile (cf. CHA:m~m~I,A~:X'.1961) would perhaps suggest a somewhat lower average proton impact energy, but the uncertainties in the energy distribution are such t h a t the average energy cannot be established from the profiles with any accuracy. This relative strength of the hydrogen lines has never been observed earlier in TromsS, in spite of the extensive spectrographic measurements (cf. \qCGARD et
and Mr. REIDULV LARSEN of the Auroral Observatory in Troms6 for their kind
Hydrogen
lines in aurora1 glow
30!)
assistance in preparing the electronic apparatus, and to Mrs. HELEN Aasm The Norwegian part of the research reported in for processing his observations. this paper was supported by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, U.S. Air Force, under contract AF 61 (051)-252 through the European Office. REFERENCES 1960
Physics of the CTpper Atrnosphrre (Ed. by J. A. Ratcliffe), ('hap.7.
ULESY K.C.,GARTLEIN C. W. and SPRAGUE G. ('HAMBERLAIN J. 1%:.
1960 1961
(:.~LPERIN ($.I. HUNTEN D.M. HUNTEN D.M. OMHOLT A. OMHOLT A. OMHOLTA. REES M.H.,BELoNA.E.~~~Ro~MIcK ROMICK G.J.~~~ELvEYC.T. \r~~~~~)I>., BERGER S. and KUNDAL
1959 1953 1955 1965 1957 19.59 1961 1958 1968
J. Geophys. Res. 65, 565. Physics of the Aurora and Airglow. Academic Press, New York. Planet. Space Sci. 1, 57. Canad. J. Phys. 31,081. ,I. Atmosph. Terr. l’hys. 7, 141. J. -4tmosph. Terr. Phys. 7, 73. J. Atmosph. Terr. Phys. 10, 320. Geofys. Publ. 20, h70. 11. Planet. Space Sci. 5, X7. .J. Atmosph. Terr. l’hys. 12, 283. Geofys. Publ. 20, No. 9.
HATES
1). Ii.
Academic Press,Xew York.
G.J. A.