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Interplanetary magnetic field structure and the variations of the ELF and VLF emissions in the topside ionosphere
Interplanetary magnetic field structure and the variations of the ELF and VLF emissions in the topside ionosphere V. I. LARKINA and JA. I. L~rtrr.rr:~ Institute OfTerrestrial
Magnetism, Ionosphere and Radio Wave Propagation Troizk, Moscow District 14x191. U.S.S.R.
I
IZMIRAN).
Absttaet - Thelntercosmos-13daIaobtainedwhenmeasuring ELFand VLFemis~ionamplitudesdurrngthe vernalequinox~~f 197Sat aurora1 latitudesand over thepolarcaps arecompared with certain IMFparameters [the potarity of the sector structure, the signs and magnitudes of rhe B, and B2 components of ihe IMF as defined in the Solar Ecliptic coordinate system (NISHWA. 1978t] The comparison shows that : (i) the positive polarity of Ihe IMF sector structure (when IMF vector is direcred m\vard the Earth) involves an enhanced probabilityofthedetectionoflargeremissionfieldintensit~es(~~~-30dB);(ii)theemis~~onmedianintensity~s -ZOdB higherat B, > Ocompared with B, < O;(iiilthe0.7? kHremission median intensltym rhepolarcaps andatnight-sideaurorallatitudesislowerwhenB, > Oascomparedwlth Hz <: O:(~\~al\ernalequinoxrherels no north-south asymmetry in the dependence of ELF and VLF r’misslon Intenhlt! on the IMF parameters.
The variations of the interplanetary magnetic field (IMF) give rise to variations in the diverse parameters of the magnetosphere and the ionosphere. The IMFrelated variations in the Earth’s magnetosphere seem to permit classi~cation into two categories. The first category includes the variations of the parameters determined directly by the state of the IMF; for example, thedimensions ofthe magnetosphere and the structure and disturbances ofthe Earth’s magnetic field (NISHIDA, 1980; FELDSTEIN, 1976). The variations of high-energy particle fluxes, especially at high altitudes in the regions of aurora1 field lines and cusps (YEAGER and FRANK. 1976). may also be classified as the direct etrects of variations in IMF, since the access of such particles to the magnetosphere is determined by the conditions of meld-line merging at the magnetospheric boundary and, therefore, is relevant to the IMF structure. The relationship of some of the magnetospheric events to the IMF are more complicated. OnI\ because their occurrence is due to the geomagnetic disturbanceand,‘or thearrivalandintensityofthehighenergy charged-particle fluxes do they reflect the IMF state. Such secondary effects include ionospheric variations (T‘K~shovA, 1982) and, in particular. some types of radio wave absorption in the ionosphere (R4PopoKr, 1980, 1981). Since the ELF and VLF emission intensity in the Earth’s niagnetosphere is known to depend on ~e(~niagnetic distllrbai~ces and on high-energy particle lluxcs. rclati[~nsliips should be expected between the IMF~~ndtl~e~ntensityandspect~oftheELFand VLF cmissionsofnatural origin.~~f,1~,4C;H1~~and D’Asc;r:~o (1%
I)
hake
obtained
a correlation
of
the
intensit)
\ariatlons of the aurora1 hilometric radiation (AKR) with lariations of the solar wind velocity and changes of sign of the IMF B,. con~ponent. The AKR intensity \\as found to increase by up to three orders of magnitude for positive B,,. Dowor\: and KLEIUMENOVA (1981) haw presented some information on the possible IMFdependent occurrence of VLF emissions (,/ --::a.5 kHz) generated in the polar cusp and observed at an Antarctic ground-based station and concluded that the enhanced ionospheric absorption, which is also related to the I\lF, make the IMF effects difficult to extract from the ground-based VLF emission data. The present paperdsals\+ith ELFand VLE‘emission amplitude variations at zuroral latitudes and in the polar caps of the Earth’s topside ionosphere. The anal! sis ivas made using the data of the Intercosmos- 13 satelhte I 1700 km apogee. 300 km perigee. 82 inclination. 99.6 min orbital period). Amplitude measurements at frequencies 0.17, 0.72 and 4.0 ktIz \vereohr,urled on 28 39 March and 7 10 April 1975. i.e. near the vernal equinox.
aector~al boundary and entered the sector slructure having the IMForientated away(ASS) from the Earth (negative polarity). On 8 April, the Earth entered TSS of I MF again ~MA~S~JK~V et ul., 1978). Thus, the mcasuremcnts have yielded approximately equal amounts of data for both polarities of the IMF sector structure. Becauseofthe high inclination ofits orbit, the satellite traversed the polar caps in the northern and southern hemispheres in the day-time and at night. Figure I shows the variations of the relative number Poftlieobservationsofadetiniteemissionamplitudein dBcalculatedForaslidingintervalof5dB width.Above and under the abscissa are plotted values of P corresponding to the TSS @ and to the ASS 8 of IMF, respectively. The mean curves were plotted using the cout~ts~orag~venampl~tudeobtained whenthesatellite tra\erscd theauroral tatitudes(60” < ~,i,< 75’)and the
Fig. I. The relative number P of the occurrence of dilferent amplittld~s of ELF and VLF emissions in dR. L’pwardr and downwards from the abscissa are plotted, respectively, the P values corresponding to TSS @ and ASS @ of IMF.
polar caps (rb > 75 ) in the day-time and at night (MLT). It can be seen that the small amplitudes were more frequently observed in ASS of IMF. whereas the high emission intensities were predominantly detected in TSS of IMF. The mean curves clearly illustrate this regularity. This regularity is seen also in cases when the number of measurements is rather small. For example, levels of the 0.17 kHz ELF emission exceeding the receiver sensitivity were detected in the polar caps and at the nightside aurora1 latitudes in not more than 40 cases out of 106 passes of the satellite. Obviously, this fact indicates that ELF emissions at this frequency are generally rare events in high latitudes. At thesame time, the relevant curves in Fig. 1 indicate that in this case alsothelarge(~~~OdB~amplitudescorrespond toTSS of IMF. The only exceptions from the above mentioned regularity are the 0.72 kHz plots for the polar caps and the nightside aurora1 region (see Fig. I) where the small amplitudes (I@20 dB) of the emission were also frequently observed in TSS of IMF. Since all the exceptions concern the same frequency, we may conclude that they constitute a characteristic feature of only those ELFemissions with/ = 0.72 kHz. Presented below will be other evidence for the specific nature of the variations of the emission at this frequency. The measurements on satellites in the solar wind have shown that the IMF strength and orjentation fluctuate rather rapidly: in particular, the interplanetary field is not always orientated along the sector axes(Krr*;c;, 1979). Such fluctuationsare not reflected in the IMF sector polari ty determined by MANSUROVel ul. (1978). We shall use the data from thecatalogue of KING (1979) to examine the dependence of ELF and VLF emission amplitudes on the magnitude and sign of the IMFcomponents. It should be borne in mind, however that K1~~‘~(I979)catalogueisincompleteanddoesnot provide simultaneous data for all ofour measurements. Figure 2 shows plots of the distribution of emission amplit~3des for the various frequencies, space regions and times ofday as a function of the magnitude and sign of the IMP B, component. Apart from points representing the measured values of the amplitude, the individual frames of Fig. 2 also show the straight lines corresponding to the median of the values for B,. > 0 and 13,.<: 0. In one of the cases where the data are evidently scanty, the B,. > 0 median was not drawn. It can be seen that the amplitude median at B, > 0 is in practice always in excess of the corresponding median at R, < 0. In conclusion, we shall examine in a similar manner rhe dependence of ELF and VLF emission amplitudes on the magnitude and sipn of the IMF H, comp~~nent
4000
-IO -6
-2
2
6
IO
-10
-6
-2
2
6
10
-10
-6
-2
2
6
Hz
IO
Fig. 2. The dist~bution of the values of ELF and VW emission amplitudes as a function of the sign and magnitude of the.iMF f.$ component for different (5.17,0.72 and 4.0 kHz) frequencies at aurora1 latitudes (60” < # <: 75”) and in the polar caps (4 > 75”) in the day-time and at night. The horizontal lines represent the amplitude median.
(see Fig. 3). The plots of Fig. 3, which are analogous to the plots of Fig. 2. reflect the sensitivity of the emission amplitudes to the IMF vector inclination to the plane of ecliptic. In most cases, the larger emission amphtudes correspond to positive values of the IMF BZ component, although the inverse trend is sometimes noticeable. The most obvious example is the 0.72 kiiz plots for the nightside aurora1 Latitudes and the polar caps in the day-time and at night. Under the given conditions, the amplitudes are smaller at 8, r 0 compared with 8, < 0. It can be shown by comparing Figs. I,2 and 3 that the emission amplitude variation at ! .= 0.72 kH2 more clearly depends on the IMF B, component sign. So. it can be concluded that the IMF H, componenl significantly reelects the 0.72 kHz emission level variations in the topside ionosphere. ‘The intensity of the natural ELF and VLF emissions depends in a rather complicated manner on the magnetospheric plasma parameters, for instance the composition and ~oncentr~~tion of “cold” particles. the Earth’s magnetic fj~l~istr~n~th and the properties of the high-energy particle fluxes. The IMF parameterdependent variations of the emission amplitudes et;amincd above are jndi~tive of the ~redon~inaI~t ifnportancc
of
fllL’
polarity
or
the
ssctnt’
structure
and
the IMF B, component. In individual cases. however, the effect ofother IMF parameters, in particular the R, component, is also perceptible. The effect of the B, component seems to be more complicated; namely. that its variations give rise todifferent variations in the amplitudes at different frequencies. The B, component sign reversal with a preserved B, sign accounts for the different character of the field line merging at the ma~netospheric boundary and, accordingly, for the different modes of the penetration of the high-energ! soIar wind particles into the magnetosphere. It is worth mentioning in this connection that we could not hnd in our data. obtained during the vernal equinox, a noticeable difference between the values measured in the northern and southern hemispheres. This is in Contrast with the observations of other geophysic;tl effects of IMF, e.g. the IMF-related variati(~i~s of the ionospheric parameters show a north-south asyntmetry at the equinoxes (TRSKOVA, 1982 ; RAPOPOKT. 1983). The results prcscnted in this paper nerd to he confirmed on the basis of more comprehensice d;nn to beobtained l~n~i~r~ii\erse~onditions. Oneoftheresults obtained, ri:. the frequency-dependence of the IM F effect in rhe emission amplitudes. may be interpreted ;rs
V. I. LARRINA and JA. 1. LIKHTER B,dB
ad0
@=60”-75”
604
Nfght
Night
-10-6
40
-2
I*
6
2
IO
Fig. 3. The same as in Fig. 2 for the IMF BLcomponent.
features of ELF and VLF emission amplitude variations may be accounted for by the fact that our analysis was based on data obtained deep in the magnetosphere, so that one may assume the influence of numerous factors, not all of which are identically related to the IMF.
a consequence of the different effects of the IMF on the intensity of the high-energy particle fluxes of various energies. It is, therefore, important to carry out an analogous analysis of the high-energy particle fluxes in a broad energy range. Such analysis, especially when based on the results of simultaneous measurements of the ELF and VLF emissions and the particle fluxes, will make possible the elucidation of the reasons for the frequency dependence of the emission amplitude variations found by us. Some of the above-described
Acknawledyemcnts-The late Dr S. M. MANSUROV inspired us to carry out this investigation. We are also indebted to Professor YA. I. FELDSTEIN and to Dr Z. Ts. RAPOPORTfor informative discussions.
REFERENCES DOWDEN R. L. and KLEIMEKOVA N. G. FELDSTEIN YA. I.
1981
J. geophys. Res. 86, 10127.
1976
Geomagnetism and the Upper Atmosphere, Vol. 3, p. 123.
1981 1979
Geophys. Res. Left. 8, 1087. Interplanetary Medium Data Book, Supplement 1 1975-
VINITI, Moscow (in Russian). GALLAGHER D. L. and D’ANGELO N.
KING J. H. MANSUKOV S. M., MANSUROVAL.G.
NISHIDA A.
RAPOFQRT Z. Ts.
and
OKULOVA L. S.
1978
1978 1980
1978. National Space Science Data Center NASA. Cataiogue OfDeterminations of the IMF Sector Polarity in 1975-1976, Antarctica, No. 17. p. 267. Nauka, Moscow (in Russian). Geamag~etic Diagnosis ofthe ~ag~erosphere.
Springer-
Verlag New York. The annual variation of the ma~eto-ionospheric disturbances, the activity asymmetry of the solar hemispheres and the interplanetary magnetic field. Part I. Preprint IZMIRAN No. 36(302), Moscow (in Russian).
Magnetic field structure and ELF and VLF emissions
9
RAPOIYXT2. Ts.
1981
The annual variation of the magneto-ionospheric disturbances, the activity asymmetry of the solar hemispheres and the interpIanetary magnetic field. Part II. Preprint IZMIRAN No. 46(359), Moscow (in Russian).
TKISKOVA L. YI:A(;I‘K D. M. and FKANKI.. A.
1982 1976
J. umos. lerr. Phys. 44, 37. J. geophys. Res. 81, 3966.
1983
Private communication.
Reference is also made to the following unpublished material:
RAP~FQRTZ. Ts.
Magnetism, Ionosphere and Radio Wave Propagation Troizk, Moscow District 14x191. U.S.S.R.
I
IZMIRAN).
Absttaet - Thelntercosmos-13daIaobtainedwhenmeasuring ELFand VLFemis~ionamplitudesdurrngthe vernalequinox~~f 197Sat aurora1 latitudesand over thepolarcaps arecompared with certain IMFparameters [the potarity of the sector structure, the signs and magnitudes of rhe B, and B2 components of ihe IMF as defined in the Solar Ecliptic coordinate system (NISHWA. 1978t] The comparison shows that : (i) the positive polarity of Ihe IMF sector structure (when IMF vector is direcred m\vard the Earth) involves an enhanced probabilityofthedetectionoflargeremissionfieldintensit~es(~~~-30dB);(ii)theemis~~onmedianintensity~s -ZOdB higherat B, > Ocompared with B, < O;(iiilthe0.7? kHremission median intensltym rhepolarcaps andatnight-sideaurorallatitudesislowerwhenB, > Oascomparedwlth Hz <: O:(~\~al\ernalequinoxrherels no north-south asymmetry in the dependence of ELF and VLF r’misslon Intenhlt! on the IMF parameters.
The variations of the interplanetary magnetic field (IMF) give rise to variations in the diverse parameters of the magnetosphere and the ionosphere. The IMFrelated variations in the Earth’s magnetosphere seem to permit classi~cation into two categories. The first category includes the variations of the parameters determined directly by the state of the IMF; for example, thedimensions ofthe magnetosphere and the structure and disturbances ofthe Earth’s magnetic field (NISHIDA, 1980; FELDSTEIN, 1976). The variations of high-energy particle fluxes, especially at high altitudes in the regions of aurora1 field lines and cusps (YEAGER and FRANK. 1976). may also be classified as the direct etrects of variations in IMF, since the access of such particles to the magnetosphere is determined by the conditions of meld-line merging at the magnetospheric boundary and, therefore, is relevant to the IMF structure. The relationship of some of the magnetospheric events to the IMF are more complicated. OnI\ because their occurrence is due to the geomagnetic disturbanceand,‘or thearrivalandintensityofthehighenergy charged-particle fluxes do they reflect the IMF state. Such secondary effects include ionospheric variations (T‘K~shovA, 1982) and, in particular. some types of radio wave absorption in the ionosphere (R4PopoKr, 1980, 1981). Since the ELF and VLF emission intensity in the Earth’s niagnetosphere is known to depend on ~e(~niagnetic distllrbai~ces and on high-energy particle lluxcs. rclati[~nsliips should be expected between the IMF~~ndtl~e~ntensityandspect~oftheELFand VLF cmissionsofnatural origin.~~f,1~,4C;H1~~and D’Asc;r:~o (1%
I)
hake
obtained
a correlation
of
the
intensit)
\ariatlons of the aurora1 hilometric radiation (AKR) with lariations of the solar wind velocity and changes of sign of the IMF B,. con~ponent. The AKR intensity \\as found to increase by up to three orders of magnitude for positive B,,. Dowor\: and KLEIUMENOVA (1981) haw presented some information on the possible IMFdependent occurrence of VLF emissions (,/ --::a.5 kHz) generated in the polar cusp and observed at an Antarctic ground-based station and concluded that the enhanced ionospheric absorption, which is also related to the I\lF, make the IMF effects difficult to extract from the ground-based VLF emission data. The present paperdsals\+ith ELFand VLE‘emission amplitude variations at zuroral latitudes and in the polar caps of the Earth’s topside ionosphere. The anal! sis ivas made using the data of the Intercosmos- 13 satelhte I 1700 km apogee. 300 km perigee. 82 inclination. 99.6 min orbital period). Amplitude measurements at frequencies 0.17, 0.72 and 4.0 ktIz \vereohr,urled on 28 39 March and 7 10 April 1975. i.e. near the vernal equinox.
aector~al boundary and entered the sector slructure having the IMForientated away(ASS) from the Earth (negative polarity). On 8 April, the Earth entered TSS of I MF again ~MA~S~JK~V et ul., 1978). Thus, the mcasuremcnts have yielded approximately equal amounts of data for both polarities of the IMF sector structure. Becauseofthe high inclination ofits orbit, the satellite traversed the polar caps in the northern and southern hemispheres in the day-time and at night. Figure I shows the variations of the relative number Poftlieobservationsofadetiniteemissionamplitudein dBcalculatedForaslidingintervalof5dB width.Above and under the abscissa are plotted values of P corresponding to the TSS @ and to the ASS 8 of IMF, respectively. The mean curves were plotted using the cout~ts~orag~venampl~tudeobtained whenthesatellite tra\erscd theauroral tatitudes(60” < ~,i,< 75’)and the
Fig. I. The relative number P of the occurrence of dilferent amplittld~s of ELF and VLF emissions in dR. L’pwardr and downwards from the abscissa are plotted, respectively, the P values corresponding to TSS @ and ASS @ of IMF.
polar caps (rb > 75 ) in the day-time and at night (MLT). It can be seen that the small amplitudes were more frequently observed in ASS of IMF. whereas the high emission intensities were predominantly detected in TSS of IMF. The mean curves clearly illustrate this regularity. This regularity is seen also in cases when the number of measurements is rather small. For example, levels of the 0.17 kHz ELF emission exceeding the receiver sensitivity were detected in the polar caps and at the nightside aurora1 latitudes in not more than 40 cases out of 106 passes of the satellite. Obviously, this fact indicates that ELF emissions at this frequency are generally rare events in high latitudes. At thesame time, the relevant curves in Fig. 1 indicate that in this case alsothelarge(~~~OdB~amplitudescorrespond toTSS of IMF. The only exceptions from the above mentioned regularity are the 0.72 kHz plots for the polar caps and the nightside aurora1 region (see Fig. I) where the small amplitudes (I@20 dB) of the emission were also frequently observed in TSS of IMF. Since all the exceptions concern the same frequency, we may conclude that they constitute a characteristic feature of only those ELFemissions with/ = 0.72 kHz. Presented below will be other evidence for the specific nature of the variations of the emission at this frequency. The measurements on satellites in the solar wind have shown that the IMF strength and orjentation fluctuate rather rapidly: in particular, the interplanetary field is not always orientated along the sector axes(Krr*;c;, 1979). Such fluctuationsare not reflected in the IMF sector polari ty determined by MANSUROVel ul. (1978). We shall use the data from thecatalogue of KING (1979) to examine the dependence of ELF and VLF emission amplitudes on the magnitude and sign of the IMFcomponents. It should be borne in mind, however that K1~~‘~(I979)catalogueisincompleteanddoesnot provide simultaneous data for all ofour measurements. Figure 2 shows plots of the distribution of emission amplit~3des for the various frequencies, space regions and times ofday as a function of the magnitude and sign of the IMP B, component. Apart from points representing the measured values of the amplitude, the individual frames of Fig. 2 also show the straight lines corresponding to the median of the values for B,. > 0 and 13,.<: 0. In one of the cases where the data are evidently scanty, the B,. > 0 median was not drawn. It can be seen that the amplitude median at B, > 0 is in practice always in excess of the corresponding median at R, < 0. In conclusion, we shall examine in a similar manner rhe dependence of ELF and VLF emission amplitudes on the magnitude and sipn of the IMF H, comp~~nent
4000
-IO -6
-2
2
6
IO
-10
-6
-2
2
6
10
-10
-6
-2
2
6
Hz
IO
Fig. 2. The dist~bution of the values of ELF and VW emission amplitudes as a function of the sign and magnitude of the.iMF f.$ component for different (5.17,0.72 and 4.0 kHz) frequencies at aurora1 latitudes (60” < # <: 75”) and in the polar caps (4 > 75”) in the day-time and at night. The horizontal lines represent the amplitude median.
(see Fig. 3). The plots of Fig. 3, which are analogous to the plots of Fig. 2. reflect the sensitivity of the emission amplitudes to the IMF vector inclination to the plane of ecliptic. In most cases, the larger emission amphtudes correspond to positive values of the IMF BZ component, although the inverse trend is sometimes noticeable. The most obvious example is the 0.72 kiiz plots for the nightside aurora1 Latitudes and the polar caps in the day-time and at night. Under the given conditions, the amplitudes are smaller at 8, r 0 compared with 8, < 0. It can be shown by comparing Figs. I,2 and 3 that the emission amplitude variation at ! .= 0.72 kH2 more clearly depends on the IMF B, component sign. So. it can be concluded that the IMF H, componenl significantly reelects the 0.72 kHz emission level variations in the topside ionosphere. ‘The intensity of the natural ELF and VLF emissions depends in a rather complicated manner on the magnetospheric plasma parameters, for instance the composition and ~oncentr~~tion of “cold” particles. the Earth’s magnetic fj~l~istr~n~th and the properties of the high-energy particle fluxes. The IMF parameterdependent variations of the emission amplitudes et;amincd above are jndi~tive of the ~redon~inaI~t ifnportancc
of
fllL’
polarity
or
the
ssctnt’
structure
and
the IMF B, component. In individual cases. however, the effect ofother IMF parameters, in particular the R, component, is also perceptible. The effect of the B, component seems to be more complicated; namely. that its variations give rise todifferent variations in the amplitudes at different frequencies. The B, component sign reversal with a preserved B, sign accounts for the different character of the field line merging at the ma~netospheric boundary and, accordingly, for the different modes of the penetration of the high-energ! soIar wind particles into the magnetosphere. It is worth mentioning in this connection that we could not hnd in our data. obtained during the vernal equinox, a noticeable difference between the values measured in the northern and southern hemispheres. This is in Contrast with the observations of other geophysic;tl effects of IMF, e.g. the IMF-related variati(~i~s of the ionospheric parameters show a north-south asyntmetry at the equinoxes (TRSKOVA, 1982 ; RAPOPOKT. 1983). The results prcscnted in this paper nerd to he confirmed on the basis of more comprehensice d;nn to beobtained l~n~i~r~ii\erse~onditions. Oneoftheresults obtained, ri:. the frequency-dependence of the IM F effect in rhe emission amplitudes. may be interpreted ;rs
V. I. LARRINA and JA. 1. LIKHTER B,dB
ad0
@=60”-75”
604
Nfght
Night
-10-6
40
-2
I*
6
2
IO
Fig. 3. The same as in Fig. 2 for the IMF BLcomponent.
features of ELF and VLF emission amplitude variations may be accounted for by the fact that our analysis was based on data obtained deep in the magnetosphere, so that one may assume the influence of numerous factors, not all of which are identically related to the IMF.
a consequence of the different effects of the IMF on the intensity of the high-energy particle fluxes of various energies. It is, therefore, important to carry out an analogous analysis of the high-energy particle fluxes in a broad energy range. Such analysis, especially when based on the results of simultaneous measurements of the ELF and VLF emissions and the particle fluxes, will make possible the elucidation of the reasons for the frequency dependence of the emission amplitude variations found by us. Some of the above-described
Acknawledyemcnts-The late Dr S. M. MANSUROV inspired us to carry out this investigation. We are also indebted to Professor YA. I. FELDSTEIN and to Dr Z. Ts. RAPOPORTfor informative discussions.
REFERENCES DOWDEN R. L. and KLEIMEKOVA N. G. FELDSTEIN YA. I.
1981
J. geophys. Res. 86, 10127.
1976
Geomagnetism and the Upper Atmosphere, Vol. 3, p. 123.
1981 1979
Geophys. Res. Left. 8, 1087. Interplanetary Medium Data Book, Supplement 1 1975-
VINITI, Moscow (in Russian). GALLAGHER D. L. and D’ANGELO N.
KING J. H. MANSUKOV S. M., MANSUROVAL.G.
NISHIDA A.
RAPOFQRT Z. Ts.
and
OKULOVA L. S.
1978
1978 1980
1978. National Space Science Data Center NASA. Cataiogue OfDeterminations of the IMF Sector Polarity in 1975-1976, Antarctica, No. 17. p. 267. Nauka, Moscow (in Russian). Geamag~etic Diagnosis ofthe ~ag~erosphere.
Springer-
Verlag New York. The annual variation of the ma~eto-ionospheric disturbances, the activity asymmetry of the solar hemispheres and the interplanetary magnetic field. Part I. Preprint IZMIRAN No. 36(302), Moscow (in Russian).
Magnetic field structure and ELF and VLF emissions
9
RAPOIYXT2. Ts.
1981
The annual variation of the magneto-ionospheric disturbances, the activity asymmetry of the solar hemispheres and the interpIanetary magnetic field. Part II. Preprint IZMIRAN No. 46(359), Moscow (in Russian).
TKISKOVA L. YI:A(;I‘K D. M. and FKANKI.. A.
1982 1976
J. umos. lerr. Phys. 44, 37. J. geophys. Res. 81, 3966.
1983
Private communication.
Reference is also made to the following unpublished material:
RAP~FQRTZ. Ts.