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Auroral hydrogen emission related to charge separation in the magnetosphere
Planet.
Space
Sci.,
1962, Vol.
9, pp. 711 to 716.
Pergamon
Press Ltd.
Pnnted
in Northern
Ireland
AURORAL HYDROGEN EMISSION RELATED TO CHARGE SEPARATION IN THE MAGNETOSPHERE W. STOFFREGEN
and H. DEREILOM Uppsala Ionospheric Observatory Research Institute of National Defence, Sweden
(Received 28 .Tme 1962) Abstract-This paper reports on some measurements on Ha(H/?) emission throughout the night in northern Sweden. The observations show that before midnight Ha emission from aurora1 glow is observed south of distinct amoral forms. After midnight no Ha(Hj3) emission is observed south of aurora1 forms but rather north of these. This is consistent with the charge separation model recently described by Axford and Hines’r). 1. INTRODUCTION
The hydrogen emissions reported here are merely concerned with aurora1 glow and an attempt is made to study the variation of Ha(H@) before and after midnight from records received at Lycksele, (geomagnetic Iatitude 62*5”N, geomagnetic longitude Ill-7”E). The variation of hydrogen emission during the night is strongly connected with theoretical considerations on the charge separation at some distance from the earth. Earlier attempts to study the amoral HGCemisssion with respect to the aurora1 theory were made by Montalbctti and Valiance Jones(2). They found a discrepancy with the prediction of Martinc3), but their observations did show a nocturnal variation of Hcc, which was later confirmed by other workers. Further investigations on the nocturnal variation of Ha were made by Romick and Elvey@), GaIperin(S), M~ville(6), and Bless, Gartlein, and Sprague”), who among other things have found that HK emission precedes an amoral display by l-2 hr. Galperin(5), and Rees, Belon, and Romick@) have reported that the Her emission is observed in the evening hours moving to the south and later during the night returning to the north, The observations reported in this paper were made with a high-speed scanning spectrophotometer which directly records the spectrogram, with recording intervals of 5 min. With this instrument it is possible to study the hydrogen emission in more detail during rapid changing aurora1 conditions. Some of these studies have been already reported in a paper on the occurrence of Her before midnight (Omholt, Stoffregen, and Derblom(g)). Observations over a longer period have now been examined in order to discover in particular what happens in the morning hours. The occurrence of Ha(HB) emission in glow and its position with respect to an electron-produced aurora before and after midnight is important for understanding of the charge separation mechanism in the magnetosphere assuming that the transport of the energetic particles follows the geomagnetic field lines towards the aurora1 zone. In a recent paper Axford and Hines(l) and FejeruO) have discussed the Ha problem in connection with their unifying theory of high-latitude geophysical phenomena and geomagnetic storms. According to their theory a charge separation of energetic particles takes place at a distance of some Earth radii in such a way that there will exist two separate shells, one of protons and one of electrons, which cross each other at noon and midnight. Before midnight theproton shell will occur closer to the Earth and after midnight the electron shell will be nearer to the Earth. During a disturbance a monoenergetic model would not be realistic. If particles of various energies are present the deformed rings will be broadened with a corresponding broadening of the precipitation zone. Further, the precipitation and 8
711
712
W. STOFFREGEN
and
H. DERBLOM
emission by protons will depend on the pitch angle distribution. It might therefore be expected that situations with strong aurora will not show a clear latitude distribution of the Hct glow and am-oral forms in accordance with the theory. In the present paper therefore situations with moderate and stable aurora only have been selected and a night variation of HM with respect to distinct aurora1 forms has been thereby obtained, which fits well with the charge separation as suggested by Axford and Hines(l). 2. THE
OBSERVATIONS
Spectrographical records from two winter periods from the Lycksele station have been analysed. For this study only a small number of records could be used. Nights with high aurora1 activity had to be excluded and since most of the records had to be analysed together with all-sky camera aurora1 films, records from clear nights only were selected. A distinction has also been made between hydrogen emission obtained from amoral glow and emission data mainly concerns hydrogen obtained from bright aurora1 forms. The obse~ational emission from diffuse glow which covers large parts of the sky. A sequence of an aurora1 film is shown in Fig. 1, where the diffuse glow is clearly visible. On the map the approximate position of the arc and the southern border of the glow is given, corresponding to the dashed lines on the aurora1 pictures. The lower border follows approximately the dip coordinates. The mean nocturnal variation of ail data is shown in Fig. 2. For comparison the N,” bands are included. The variation is in agreement with other observations mentioned before. The maximum of the hydrogen emission appears earlier than the maximum of N,+ bands and at the Lycksele station the number of H/l occurrences is considerably less after midnight than before. The figure also gives an impression of the ratio between the occurrence of the H/I line and N2+ bands. A number of detailed observations are assembled in Fig. 3. All these diagrams show, on
FIG. 2. THEMEAN
NIGHTVARIATION OFHBEMISSIONANDN~~
(4278 A) BAND.
1920
l KIRUNA
19'0
1925 DIP 75
1920 1925 20'0
FIG.~. MAPSHOWINGTHEAPPROXIMATEPOSITIONOFANARCANDTHESOUTHERNBORDEROFHYDROGENGLOW ASSEEN ON ALL-SKY PICTURES FROM LYCKSELE FEBR. 26,1962. THE DIP LONE FOR 75" IS DRAWN AS A DASHED LINE.
712
AURQRAL
HYDROGEN
EMISSION
RELATED
TO CHARGE
SEPARATXON
713
the upper part, the variation of aurora scaled from am-oral films (aseafilms). The zenith line in all these cases is on the line of sight of the spectrograph. For comparison the H/S and Nzi (4278 A) curves are drawn below. The I-r6 intensity scale has been enlarged about 6ve times. The aurora1 forms are plotted according to the legend given on the figure and represent a small band covering the sky from the northern to the southern horizon. LYCKSELE
GEOM LAI.
; GLOW
6z.s”
1 HOM
30 3 60
26262
FIG.~.
1 RAYED AURORA
j PULS
AURORA AUC?ORA
1 10 60
18 1 61
3460
SELECIED DIAGRAMS SROWING THEVARIATIONOFAURORA(UPPERPARTOF EACHDIAGRAM)AND CORRESPONDING VARIATION OF H/Z AND N,+ INTENSITIES. ENCIRCLEDNUMBERS REFER TO TEXT.
THE
714
W.
STOFFREGEN
and H. DERBLOM
The record from 7 December 1960 shows at the beginning (arrow I) a glow showing strong HP emission. At 2 the aurora1 glow again passes the zenith with simultaneous H@ record. At 3 the stronger aurora moves southwards and no H/3 is recorded north of it. During the period 00.30 hr-03.00 hr the aurara is mainly south of the zenith, but at 4, H/3 is strongly recorded in the zenith, An interesting passage is marked 5 and it is clearly seen that no HP emission was found south of the distinct aurora at about 03.15 hr. This part of the figure is a rather good illustration of the tendency, which might be expected according to the model of Axford and Hines”). In the next part of the figure, from 30 September 1960 to 1 October 1960, the same tendency is clearly seen. At 6 the glow in the zenith is accompanied by HB emission, whereas in the morning (01.30 hr) an aurora in the zenith shows no HP on the records (7). The record from 7 November 1961 shows the same configuration at 8 and II respectively. It is interesting to see that at 9 (20.55 hr) no HP is found north of the distinct aurora1 form. when this moves over the zenith. The absence of glow and HP at I0 is also in agreement with the general tendency. The record from 11 February 1962 shows again the occurrence of HP north of an aurora around Ol*OOhr (12) and the absence of H/3 south of the aurora at 02.00 hr (13). The last part of the figure shows two evening situations, (26 February 1962 and 18 January 1961) with glow and H/3 south of the distinct aurora (14 and 15). The morning situation on 3 April 1960 shows only HP emission, when the strong aurora had moved far to the south (16). In this figure special occasions have been selected but the general tendency outlined here is more or less readily visible in a great number of other scalings. All observations have been assembled in the diagram shown in Fig. 4. This diagram shows the occurrence in per cent of d@erent types of aurora in the north, zenith and south ranges, when H@$i cc) is recorded in zenith. When hydrogen emission is observed in the zenith range in the evening hours, it can be clearly seen that the greatest number of aurora1 forms is of the glow type. In the early evening hours there is a very well-pronounced tendency for aurora1 forms to be north of the Lycksele station, when HP is observed in the zenith. In the morning hours, especially between 01.00 hr and 03.00 hr there are always aurora1 forms south of Lycksele, when hydrogen emission is observed in the zenith. The hydrogen emission observed in the morning hours is also here mostly connected with aurora1 glow. It can be seen from this diagram, that there is a more or less diffuse situation around midnight lasting from 21.00 hr to 01.00 hr. 3.
CONCLUSIONS
The observations described above can be summarized as follows. I. The hydrogen emission at the Lycksele station (sub-aurora1 zone) occurs most frequently in the early evening hours with a maximum around 20.30 hr. The emission from N,f bands, which represents the aurora1 activity, has a maximum around 22.30 hr. The hydrogen emission precedes the general aurora1 activity by about 2 hr. 2. A glow covering large areas of the sky is the most frequently observed type of aurora, when hydrogen emission is present. This glow can be intensified in its southern boundary and appear as a homogeneous arc for an observer at some distance. 3. When hydrogen lines associated with glow are recorded in the zenith the main aurora1 forms in the evening hours are present to the north of the Her glow and in the morning hours aurora1 forms appear to the south of the Ha glow. Around midnight the situation is more diffuse and complicated. An important question is at which latitude the position of amoral forms versus hydrogen
AURORAL
HYDROGEN
EMISSION
RELATED
TO CHARGE
SEPARATION
715
during the night is most pronounced. The precipitation of energetic particles from the equatorial plane in the magnetosphere involves a number of impI~~ations as mentioned above. The geomagnetic latitude of Lycksele, 623” N (75” dip> corresponds to a geomagnetic field line 1 = 4.2 earth radii and seems to be near the lowest latitude, where this Hg glow reasonably could be observed except for anomalous conditions. glow
LYCKSELE ~1
62,5cl GEOM. LAT.
50 40 30 2Q
1
10 0
t
% 50 40 30
!
2+ lOi_ *L % 40 30
t
r 20y IO!20
FIG. 4.
DIAGRAM
TYPES OF AURORA
30”s
OFF ZENffH)
22
SHOWINCI IN NORTH AND
THE
00
02
OCCURRENCE
RANGE,
SQIJTfI RANGE,
ZENITH WHEN
LT
OF DIFFERENT
RANGE
f 30%-
z-
N/? IS OBSERVED
IN ZENITH.
The aurora1 glow here associated with proton impact usually forms a belt of a few degrees of latitude, whilst the aurora1 forms produced by electrons cover a much smaller range of latitude. At which part of the total path the protons are spread is not clear, although one can expect that this already is the case in the equatorial plane, Concerning the night variation it seems that the crossover point is somewhat earlier than midnight and that between 22.00 hr and 01 .OOhr the situation is more complex. One cannot expect a more regular night variation of such a complicated phenomenon as the aurora and one has to keep in mind that the theoretical picture of th.e charge separation outside the earth’s atmosphere is an idealized one. During nights with a strong aurora and sudden increases of activity the relative appearance of aurora1 forms and hydrogen glow no longer follows the pattern described above. The best situations for this study are obtained, when glow occurs together with quiet, homogeneous arcs and bands. In spite of these limitations the observations are consistent with the crossover of an electron shell and a proton shell as described by Axford and Hines. It is highly desirable to
716
W. STOFFREGEN
and H. DERBLOM
make studies at latitudes within and north of the aurora1 zone in order to complete picture over the whole relevant range of latitudes.
the
would like to express our sincere thanks to Dr. C. 0. Hines and Dr. A. Omholt for valuable discussions of the observations, to Mr. B. Anger for scaling the material and to Mr. A. Burstriim and Mr. A. Blckstriim for carrying out the observations.
Acknowledgements-We
REFERENCES 1. W. I. AXFORDand C. 0. HINES, Canad. 1. Phys. 39, 1433 (1961). 2. R. MON~ALBETTI and A. VALLANCEJONES,J. Atmos. Terr. Phys. 11,43 (1957). 3. D. F. MARTYN,Nature, Lond. 167, 92 (1951). 4. G. J. ROMICK,and C. T. ELVEY,J. Atmos. Terr. Phys. 12, 283 (1958). 5. G. I. GALPERIN,Planet. Space Sci. 1, 57 (1959). 6. J. M. MALVILLE,J. Geophys. Res. 64, 1389 (1959). 7. R. C. BLESS,C. W. GARTLEINand G. SPRAGUE,J. Geophys. Res. 65, 565 (1960). 8. M. H. REES,A. E. BELON and G. J. ROMICK,Planet. Space Sci. 5,87 (1961). 9. A. OMHOLT,W. S~OFFREGEN and H. DERBLOM,J. Atmos. Terr. Phys. 24,203 (1962). 10. J. A. FEJER,Cunad. J. Phys. 39, 1409 (1961).
Space
Sci.,
1962, Vol.
9, pp. 711 to 716.
Pergamon
Press Ltd.
Pnnted
in Northern
Ireland
AURORAL HYDROGEN EMISSION RELATED TO CHARGE SEPARATION IN THE MAGNETOSPHERE W. STOFFREGEN
and H. DEREILOM Uppsala Ionospheric Observatory Research Institute of National Defence, Sweden
(Received 28 .Tme 1962) Abstract-This paper reports on some measurements on Ha(H/?) emission throughout the night in northern Sweden. The observations show that before midnight Ha emission from aurora1 glow is observed south of distinct amoral forms. After midnight no Ha(Hj3) emission is observed south of aurora1 forms but rather north of these. This is consistent with the charge separation model recently described by Axford and Hines’r). 1. INTRODUCTION
The hydrogen emissions reported here are merely concerned with aurora1 glow and an attempt is made to study the variation of Ha(H@) before and after midnight from records received at Lycksele, (geomagnetic Iatitude 62*5”N, geomagnetic longitude Ill-7”E). The variation of hydrogen emission during the night is strongly connected with theoretical considerations on the charge separation at some distance from the earth. Earlier attempts to study the amoral HGCemisssion with respect to the aurora1 theory were made by Montalbctti and Valiance Jones(2). They found a discrepancy with the prediction of Martinc3), but their observations did show a nocturnal variation of Hcc, which was later confirmed by other workers. Further investigations on the nocturnal variation of Ha were made by Romick and Elvey@), GaIperin(S), M~ville(6), and Bless, Gartlein, and Sprague”), who among other things have found that HK emission precedes an amoral display by l-2 hr. Galperin(5), and Rees, Belon, and Romick@) have reported that the Her emission is observed in the evening hours moving to the south and later during the night returning to the north, The observations reported in this paper were made with a high-speed scanning spectrophotometer which directly records the spectrogram, with recording intervals of 5 min. With this instrument it is possible to study the hydrogen emission in more detail during rapid changing aurora1 conditions. Some of these studies have been already reported in a paper on the occurrence of Her before midnight (Omholt, Stoffregen, and Derblom(g)). Observations over a longer period have now been examined in order to discover in particular what happens in the morning hours. The occurrence of Ha(HB) emission in glow and its position with respect to an electron-produced aurora before and after midnight is important for understanding of the charge separation mechanism in the magnetosphere assuming that the transport of the energetic particles follows the geomagnetic field lines towards the aurora1 zone. In a recent paper Axford and Hines(l) and FejeruO) have discussed the Ha problem in connection with their unifying theory of high-latitude geophysical phenomena and geomagnetic storms. According to their theory a charge separation of energetic particles takes place at a distance of some Earth radii in such a way that there will exist two separate shells, one of protons and one of electrons, which cross each other at noon and midnight. Before midnight theproton shell will occur closer to the Earth and after midnight the electron shell will be nearer to the Earth. During a disturbance a monoenergetic model would not be realistic. If particles of various energies are present the deformed rings will be broadened with a corresponding broadening of the precipitation zone. Further, the precipitation and 8
711
712
W. STOFFREGEN
and
H. DERBLOM
emission by protons will depend on the pitch angle distribution. It might therefore be expected that situations with strong aurora will not show a clear latitude distribution of the Hct glow and am-oral forms in accordance with the theory. In the present paper therefore situations with moderate and stable aurora only have been selected and a night variation of HM with respect to distinct aurora1 forms has been thereby obtained, which fits well with the charge separation as suggested by Axford and Hines(l). 2. THE
OBSERVATIONS
Spectrographical records from two winter periods from the Lycksele station have been analysed. For this study only a small number of records could be used. Nights with high aurora1 activity had to be excluded and since most of the records had to be analysed together with all-sky camera aurora1 films, records from clear nights only were selected. A distinction has also been made between hydrogen emission obtained from amoral glow and emission data mainly concerns hydrogen obtained from bright aurora1 forms. The obse~ational emission from diffuse glow which covers large parts of the sky. A sequence of an aurora1 film is shown in Fig. 1, where the diffuse glow is clearly visible. On the map the approximate position of the arc and the southern border of the glow is given, corresponding to the dashed lines on the aurora1 pictures. The lower border follows approximately the dip coordinates. The mean nocturnal variation of ail data is shown in Fig. 2. For comparison the N,” bands are included. The variation is in agreement with other observations mentioned before. The maximum of the hydrogen emission appears earlier than the maximum of N,+ bands and at the Lycksele station the number of H/l occurrences is considerably less after midnight than before. The figure also gives an impression of the ratio between the occurrence of the H/I line and N2+ bands. A number of detailed observations are assembled in Fig. 3. All these diagrams show, on
FIG. 2. THEMEAN
NIGHTVARIATION OFHBEMISSIONANDN~~
(4278 A) BAND.
1920
l KIRUNA
19'0
1925 DIP 75
1920 1925 20'0
FIG.~. MAPSHOWINGTHEAPPROXIMATEPOSITIONOFANARCANDTHESOUTHERNBORDEROFHYDROGENGLOW ASSEEN ON ALL-SKY PICTURES FROM LYCKSELE FEBR. 26,1962. THE DIP LONE FOR 75" IS DRAWN AS A DASHED LINE.
712
AURQRAL
HYDROGEN
EMISSION
RELATED
TO CHARGE
SEPARATXON
713
the upper part, the variation of aurora scaled from am-oral films (aseafilms). The zenith line in all these cases is on the line of sight of the spectrograph. For comparison the H/S and Nzi (4278 A) curves are drawn below. The I-r6 intensity scale has been enlarged about 6ve times. The aurora1 forms are plotted according to the legend given on the figure and represent a small band covering the sky from the northern to the southern horizon. LYCKSELE
GEOM LAI.
; GLOW
6z.s”
1 HOM
30 3 60
26262
FIG.~.
1 RAYED AURORA
j PULS
AURORA AUC?ORA
1 10 60
18 1 61
3460
SELECIED DIAGRAMS SROWING THEVARIATIONOFAURORA(UPPERPARTOF EACHDIAGRAM)AND CORRESPONDING VARIATION OF H/Z AND N,+ INTENSITIES. ENCIRCLEDNUMBERS REFER TO TEXT.
THE
714
W.
STOFFREGEN
and H. DERBLOM
The record from 7 December 1960 shows at the beginning (arrow I) a glow showing strong HP emission. At 2 the aurora1 glow again passes the zenith with simultaneous H@ record. At 3 the stronger aurora moves southwards and no H/3 is recorded north of it. During the period 00.30 hr-03.00 hr the aurara is mainly south of the zenith, but at 4, H/3 is strongly recorded in the zenith, An interesting passage is marked 5 and it is clearly seen that no HP emission was found south of the distinct aurora at about 03.15 hr. This part of the figure is a rather good illustration of the tendency, which might be expected according to the model of Axford and Hines”). In the next part of the figure, from 30 September 1960 to 1 October 1960, the same tendency is clearly seen. At 6 the glow in the zenith is accompanied by HB emission, whereas in the morning (01.30 hr) an aurora in the zenith shows no HP on the records (7). The record from 7 November 1961 shows the same configuration at 8 and II respectively. It is interesting to see that at 9 (20.55 hr) no HP is found north of the distinct aurora1 form. when this moves over the zenith. The absence of glow and HP at I0 is also in agreement with the general tendency. The record from 11 February 1962 shows again the occurrence of HP north of an aurora around Ol*OOhr (12) and the absence of H/3 south of the aurora at 02.00 hr (13). The last part of the figure shows two evening situations, (26 February 1962 and 18 January 1961) with glow and H/3 south of the distinct aurora (14 and 15). The morning situation on 3 April 1960 shows only HP emission, when the strong aurora had moved far to the south (16). In this figure special occasions have been selected but the general tendency outlined here is more or less readily visible in a great number of other scalings. All observations have been assembled in the diagram shown in Fig. 4. This diagram shows the occurrence in per cent of d@erent types of aurora in the north, zenith and south ranges, when H@$i cc) is recorded in zenith. When hydrogen emission is observed in the zenith range in the evening hours, it can be clearly seen that the greatest number of aurora1 forms is of the glow type. In the early evening hours there is a very well-pronounced tendency for aurora1 forms to be north of the Lycksele station, when HP is observed in the zenith. In the morning hours, especially between 01.00 hr and 03.00 hr there are always aurora1 forms south of Lycksele, when hydrogen emission is observed in the zenith. The hydrogen emission observed in the morning hours is also here mostly connected with aurora1 glow. It can be seen from this diagram, that there is a more or less diffuse situation around midnight lasting from 21.00 hr to 01.00 hr. 3.
CONCLUSIONS
The observations described above can be summarized as follows. I. The hydrogen emission at the Lycksele station (sub-aurora1 zone) occurs most frequently in the early evening hours with a maximum around 20.30 hr. The emission from N,f bands, which represents the aurora1 activity, has a maximum around 22.30 hr. The hydrogen emission precedes the general aurora1 activity by about 2 hr. 2. A glow covering large areas of the sky is the most frequently observed type of aurora, when hydrogen emission is present. This glow can be intensified in its southern boundary and appear as a homogeneous arc for an observer at some distance. 3. When hydrogen lines associated with glow are recorded in the zenith the main aurora1 forms in the evening hours are present to the north of the Her glow and in the morning hours aurora1 forms appear to the south of the Ha glow. Around midnight the situation is more diffuse and complicated. An important question is at which latitude the position of amoral forms versus hydrogen
AURORAL
HYDROGEN
EMISSION
RELATED
TO CHARGE
SEPARATION
715
during the night is most pronounced. The precipitation of energetic particles from the equatorial plane in the magnetosphere involves a number of impI~~ations as mentioned above. The geomagnetic latitude of Lycksele, 623” N (75” dip> corresponds to a geomagnetic field line 1 = 4.2 earth radii and seems to be near the lowest latitude, where this Hg glow reasonably could be observed except for anomalous conditions. glow
LYCKSELE ~1
62,5cl GEOM. LAT.
50 40 30 2Q
1
10 0
t
% 50 40 30
!
2+ lOi_ *L % 40 30
t
r 20y IO!20
FIG. 4.
DIAGRAM
TYPES OF AURORA
30”s
OFF ZENffH)
22
SHOWINCI IN NORTH AND
THE
00
02
OCCURRENCE
RANGE,
SQIJTfI RANGE,
ZENITH WHEN
LT
OF DIFFERENT
RANGE
f 30%-
z-
N/? IS OBSERVED
IN ZENITH.
The aurora1 glow here associated with proton impact usually forms a belt of a few degrees of latitude, whilst the aurora1 forms produced by electrons cover a much smaller range of latitude. At which part of the total path the protons are spread is not clear, although one can expect that this already is the case in the equatorial plane, Concerning the night variation it seems that the crossover point is somewhat earlier than midnight and that between 22.00 hr and 01 .OOhr the situation is more complex. One cannot expect a more regular night variation of such a complicated phenomenon as the aurora and one has to keep in mind that the theoretical picture of th.e charge separation outside the earth’s atmosphere is an idealized one. During nights with a strong aurora and sudden increases of activity the relative appearance of aurora1 forms and hydrogen glow no longer follows the pattern described above. The best situations for this study are obtained, when glow occurs together with quiet, homogeneous arcs and bands. In spite of these limitations the observations are consistent with the crossover of an electron shell and a proton shell as described by Axford and Hines. It is highly desirable to
716
W. STOFFREGEN
and H. DERBLOM
make studies at latitudes within and north of the aurora1 zone in order to complete picture over the whole relevant range of latitudes.
the
would like to express our sincere thanks to Dr. C. 0. Hines and Dr. A. Omholt for valuable discussions of the observations, to Mr. B. Anger for scaling the material and to Mr. A. Burstriim and Mr. A. Blckstriim for carrying out the observations.
Acknowledgements-We
REFERENCES 1. W. I. AXFORDand C. 0. HINES, Canad. 1. Phys. 39, 1433 (1961). 2. R. MON~ALBETTI and A. VALLANCEJONES,J. Atmos. Terr. Phys. 11,43 (1957). 3. D. F. MARTYN,Nature, Lond. 167, 92 (1951). 4. G. J. ROMICK,and C. T. ELVEY,J. Atmos. Terr. Phys. 12, 283 (1958). 5. G. I. GALPERIN,Planet. Space Sci. 1, 57 (1959). 6. J. M. MALVILLE,J. Geophys. Res. 64, 1389 (1959). 7. R. C. BLESS,C. W. GARTLEINand G. SPRAGUE,J. Geophys. Res. 65, 565 (1960). 8. M. H. REES,A. E. BELON and G. J. ROMICK,Planet. Space Sci. 5,87 (1961). 9. A. OMHOLT,W. S~OFFREGEN and H. DERBLOM,J. Atmos. Terr. Phys. 24,203 (1962). 10. J. A. FEJER,Cunad. J. Phys. 39, 1409 (1961).