- Email: [email protected]
Effects of IMF polarity on the F2-region
Effects of IMF polarity on the B-region L.TR~sKwA Geophysical
Institute,
Czechoslovak
Academy
of Sciences, BoEni 11, 141 31 Prague
4, Czechoslovakia
Abstract--On the basis of data from nineteen ionospheric stations in both hemispheres it is shown that the effect ofthesectorial structureoftheIMFappears in the FZ-region asa response to thechanges in geomagnetic activity caused by the changes of the IMF polarity. It is most pronounced in the nighttime,~~FZ in equinoxial periods at solar m~~ximum.
INTRODUCTION The (IMF)
Influence on
of the interplanetary
properties
of
the
INITIAL DATA, METHOD 01; ANALYSIS magnetic
magnetosphere
field
HourlyibF2-values, measured by vertical sounding stations, have been used as initial data; the list of stations is given in Table 1.The selected stations should ideafly cover the largest possible range of latitudes in both hemispheres but in practice the choice was, of course, limited by the stations for which data were available. The geomagnetic latitudes of these stations corresponded to L-values between 1.08 and 4.33. Equinoxial periods for the maxima of the 19th, 20th and 21st solar cycle have been analyzed. Median ,fi~F2values for the individual months were determined separately for days with positive and negative IMF polarity, i.e. away from, and towards the Sun respectively. The polarity ofthe IMF for the individual days of the 19th and 20th cycle was determined after SVALGAAKD (1975) and MANSURW cf al. (1976): only
and
ionosphere has become the object of much research in recent years. The effects of the changes in the IMF polarity on the lower ionosphere and, thereby, on the reflection or absorption of radio waves can be considered as proved (SCHLEGELet ul., 1977; OKSMAN and RANTA, 1979; LASTOVICKA, 1979; OKSMAN and RANTA, 1980). The effects of the IMF sectorial structure on the F2-layer are not very clear since they are expected to be obscured by other influences that are more important for this layer. Most papers, dealing with the IMF influence on the F’?-layer, study the effect of the sector boundary crosstng. For example, D’ANGELO (1980) has studied the dependence of FZ-layer critical frequencies on the state of the IMF from the point of view of electrodynamic coupling between high- and lowlatitude regions, and he also notes a decrease of,foF2 during the first day after crossing the sector boundary, Attention to the inffuence of sector boundary crossing on the total electron content and on F2-layer parameters has also been paid by LYON and BHATANGAK(1979), however, the dependence obtained is less pronounced than that found by D’Angelo. The state of the F2-layer on days with different IMF polarities has been studied by SHAPIROand POTAPOVA (1974) and PWAKWA and SHAPIRO (1974). They pointed out that the effecect of the interplanetary magnetic field during magnetically quiet periods can cause day-to-day fluctuations of the ionospheric parameters and strong changes in nighttime heights of the F2-region. In this paper, the results are given of an investigation on IMF effects on the FZ-layer as obtained by evaluating data from thirteen ionospheric stations in the Northern Hemisphere and six in the Southern Hemisphere.
Table I
37
Station
Geographic latitude longitude
Salechard Jakutsk Juliusruh Lindau Prahonice Wakkanai Simferopol Sofia Ebro Akita Kukubunji Yamagdwa Dalhi
66.58”N 62.05”N 54.63 N 51.65’N 49.99“N 45.4VN 44.83’ N 42.70“N 40.81’.N 39.73’N 35.7@ N 31.20’N 28.63’N
66.67”E 129.67”E 13.38”E 10.13”E 14.55’ E 141.6X”E 34.07’ E 23.3S’.E 0.49’ E I40.13”E 139.48”E 130.65&E 77 I27”E I
Townsville Brisbane Canberra Hobart Christchurch Campbell Island
19.10’5 27.53”s 35.32”s 42.92”s 43.57”s 52.55”s
146.50”E 152.92’E 149.00”E 141.17’E 172.80”E 167.15’E
Invariant latitude
61.28’ 55.13 51.67 4X.86 46.15 36.X2 40.52 37.76 37.05 30.25 25.62’ 19.83 15.19 -26.10 - 35.53 -44.86 - 53.60 -49.80 -59.92’
_
1. 4.33 3.06 2.60 2.31 1.13
1.56 1.71 I.60 1.57 1.34 1.23 I.13
I .0x 1.24 1.51 1.99 2.84 2.40 3.98
L. TRis~ovA
38
data for those days, for which the polarity was identical according to both catalogues, were considered. Data published in Sob Geophysical Data (424-Part I, 38, December 1979) were used for the 21st cycle. The selection process described above naturally decreased the volume of data to be examined, and the question arose whether the results obtained would in thesecircumstances have any physical significance. The IMF influence on foF2 is only a secondary effect and for a simple statistical evaluation based on median values it might well be obscured by other factors. Data from two mid-latitude ionosphere stations, Lindau and Prfihonice, which are near to one another, were chosen for the initial investigation. At both stations, the local time dependence offoF is almost identical. Theinitialassumption was that within agiven time period an ,fijF2-deviation on days with different IMF polarity should have the same sense at both stations. This assumption has really been confirmed for the whole period under consideration. An example of results obtained is shown in Fig. 1where the medians of hourly ji)F2-values are plotted against local time. Almost smooth curves are obtained for nighttime hours, whereas the daytime shows larger differences between both stations. In the latter case, the lack of processed data may become important: a sounder
0
6
12
18
11
Fig. 1. Diurnal variation offoF median values with respect to the IMF polarity vs local time. Northern mid-latitude stations : Lindau A = + polarity, A = - polarity: Prahonice l = + polarity, 0 = - polarity.
failure or local interference at one station can cause a considerable shift of the median value compared with the same value from the other station. Despite this, however, the shift in the median values for days with different IMF polarity always shows the same sense and its magnitude is comparable at both stations. Thus it can be assumed that information obtained by simply determining the ,foF2-medians separately for days with positive and negative IMF polarity is of physical significance and can, therefore, be safely used to investigate the influence of the IMF sectorial structure on the F2-layer. RESULTS
From an analysis of the whole period under investigation it is found that in the daytime practically no consistent features can be found for,foF2-values on days with different IMF polarity. For example, at latitude 50”N (stations Lindau and Pruhonice), the medianfoF2-value in 1969 is always higher for days with negative IMF polarity while in 1957 and 1968 this is valid only for March and October, in 1958 only for September, in 1959 for September and October, in 1970 for October, and no such case occurred in 1979. Certain typical features could be found for nighttime hours when the geomagnetic held is the only permanent factor which, together with local electric fields (E W component), affects the critical F2-layer frequency.
11
Fig. 2a. Median nighttime values offoF
with respect to the IMF polarity vs local time. Northern mid-latitude stations: Lindau A = + polarity, A = - polarity; PrShonice 0 = + polarity, 0 = - polarity.
Effects of IMF polarity
35,
on the F2-region I
2
3
4
. 6. 1 :
:
b..
0
.APR l
.O
.
l
0 0 .
0
”
OCTY o.
b
Fig. 2b. Median nighttime values offoF with respect to the IMF polarity vs local time. Southern mid-latitude station: Hobart 0 = + polarity, 0 = - polarity.
Fig. 3. Values of the representative factor B calculated from definition (1) vs L-parameter: l = data for the year 1958, x = data for the year 1969.
At both northern and southern mid-latitudes, smaller medianfoF2-values were found in March and April for days with negative IMF polarity, whereas in September and October higher values occurred for days with negative polarity. An example of the.foF2 variation with local time is shown in Fig. 2 where results of the analysis of data from Lindau, Prdhonice and Hobart are given for equinoxial periods of the 19th, 20th and 21 st solar cycle maxima. In order to make a comparison of the results from different stations possible, a representative factor
variation of the B-factor as derived from Lindau and Juliusruh (data measured during 1958 in the maximum ofthe 19th solar cycle) and corresponding K-indices for days with negative IMF polarity.
XI”
B=---
-cf-.+
* 100
Cf
was introduced wherej ’ is the medianfoF2-value for days with positive IMF polarity in a given month,fis the same for days with negative polarity. The sum includes hourly values between 22 and 06 hours local time. A positive value of B thus represents higher critical FZ-layer frequencies on days with positive IMF polarity. Values of the B-factor for the individual months are plotted in Fig. 3 vs L-values corresponding to the stations listed in Table 1. It will be seen that the phenomenon shown in Fig. 2 (lower critical frequencies on days with negative IM F polarity in March and April and higher in September and October) is true for practically all the stations studied in this analysis. For the sake ofcompleteness, Fig. 4 shows the annual
DISCUSSION
For the circumstances described above (the use of simple medians, low number of values), the B-factor as defined in the preceding section has to be considered as a rather qualitative index. Nevertheless, the results shown in Figs 2,3,4 suggest some general conclusions. The phenomenon established herein, i.e. that nighttimeSoF on days with negative IMF polarity are lower in March and April and higher in September and October than on days with positive IMP polarity can be considered an objective fact. This is a planetary phenomenon appearing equally in both hemispheres over a considerable range of latitudes, and it is in accordance with investigations of the dependence of geomagnetic field changes on the IMF polarity. It is also in accordance, for example, with Fig. 1 in D’ANGELO’S paper (1980) where average values offoF from Lindau and Dourbes are plotted for 00-03 hours LT for every day of the period 1 April to 31 December 1974. The disagreement with this conclusion for some results (from stations with geographic longitudes
40
Fig. 4. Annual variation of the factor B m 195X and average K-indices l’or days with negative IMF polarity: = Lindau, ---- = Juliusruh (lack of data in May), x = K,, 0 = K-index measured at the Prilhonice station, l = K’( = average K-index calculated for night hours only).
exceeding 130’E) could be expiained by a possible inaccurate coordination of the IMF polarity to individual days since the day polarities as given in the catalogues used, refer to the zero meridian, or by exceptional local magnetic activity in the given region. Taking into account the fact that the average critical F2-layer frequencies decrease on days of enhanced geomagnetic activity (effect of the negative phase of geomagnetic storms), this phenomenon confirms the annual variation of geomagnetic activity with two maxima in the equinoxial periods as well as their distribution according to IMF polarity (R~sstit and M~PHERRON, 1973; BUNCH, 1973; B~~~~~ELI~K,1975). For example, the planetary Am-index shows two maxima in its annual variation at the equinoxial periods, attaining for days with negative IMF polarity (direction towards the Sun) maximum values only in the first half and for days with positive polarity only in the second half of the year. The annual varjation of the aurora1 Ah-index shows one maximum, but two maxima appear at the equinoxial periods when thedays aredividedas to their IMF~~~~~~~~(BEKTwELIER,1976). The annual variation of the B-factor (Fig. 4) is also in qualitative accordance with the annual variation of geomagnetic activity on days with negative IMF polarity as given in the papers referred to above. At the same time the changes in the B-factor reflect the nature of changes in geomagnetic activity on days with negative IMF polarity since, with increasing geomag-
netic activity on these days, 3 increases as a result of the decreasing sum C,f -- in definition (I). Differences in ,ji)F2 on days with different IMF polarity tend to be larger at larger geomagnetic latitudes. For most of the stations investigated here with L > 2, this dilIerence is 1tr-ZSl?;,. The above results refer to the maximum periods of the 19th, 20th and 2lst solar cycles. A similar analysis made for the period of solar minimum (1964) did not yield an unambiguous result.
From the results presented here it can be suggested that the effect of the sectorial structure of the IMF appears in the F2-region as a response to changes in geomagnetic activity caused by the changes of the IMF polarity. It is really observable only during nighttime hours since it is obscured by other factors during the daytime. This phenomenon is most pronounced in equinoxial periods at solar maximum. It is effective in both hemispheres in that average nighttime ,fiFZvalues are lower on days with negative IMF polarity in March and April, and higher in September and October thanondayswithpositi~~eIMFpolarity.In therangeof invariant latitudes of 45-66 the magnitude of this difference reaches about 202, and even more in the period under investigation. and it shows an increasing trend with increasing geomagnetic latitude.
REFERENCE BERTHELIEKA. BERTWELIER A.
1975 1976
BURCHJ. L.
1973
D’ANC;ELO N. LASTOVI?KA J. LYON G. F. and BHATANGAR V. P. MANSIJROV S. M., MANSUROV G. S. and M~NSUUO~A
1980 1979
L. G.
I979 1976
CT.r. Acud. Sci., Ser. B 280, J. geophys. Rex 81, 4546. J. geophys. Res. 78, 1047. Can. J. Phys. 58, 693.
195.
J. atmos. terr. Phys. 41, 995. Can. J. Phys. 57, 21X. ‘~nturktika 15, 16.
Effects of IMF polarity J. and RANTA H. J. and RANTA H. RUSSE:L.L C. T. and MCPHEKKON R. L. POTAPOVAN. I. and SHAPIKO B. S. S~HLIXXL K.. ROSE G. and WIUDEL H. U. SHA~IKO B. S. and P~TAP~VA N. 1. SVMX \*Iw I_ OKSMAN OKSMAN
1979 1980 I973 1974 1977 1974 1975
on the F2-region IAGA Bullerin 43, 311. Planet. Space Sci. 28, I I55 J. geophys. Rex 78, 92. Gromagn. Aeron. 14, I 101. ./. utwx [err. Phys. 39, 101. Guomagn. Aeron. 14, 1099. SUIPR Report No. 629, Institute for Plasma Stanford University, Stanford, California.
41
Research,
Institute,
Czechoslovak
Academy
of Sciences, BoEni 11, 141 31 Prague
4, Czechoslovakia
Abstract--On the basis of data from nineteen ionospheric stations in both hemispheres it is shown that the effect ofthesectorial structureoftheIMFappears in the FZ-region asa response to thechanges in geomagnetic activity caused by the changes of the IMF polarity. It is most pronounced in the nighttime,~~FZ in equinoxial periods at solar m~~ximum.
INTRODUCTION The (IMF)
Influence on
of the interplanetary
properties
of
the
INITIAL DATA, METHOD 01; ANALYSIS magnetic
magnetosphere
field
HourlyibF2-values, measured by vertical sounding stations, have been used as initial data; the list of stations is given in Table 1.The selected stations should ideafly cover the largest possible range of latitudes in both hemispheres but in practice the choice was, of course, limited by the stations for which data were available. The geomagnetic latitudes of these stations corresponded to L-values between 1.08 and 4.33. Equinoxial periods for the maxima of the 19th, 20th and 21st solar cycle have been analyzed. Median ,fi~F2values for the individual months were determined separately for days with positive and negative IMF polarity, i.e. away from, and towards the Sun respectively. The polarity ofthe IMF for the individual days of the 19th and 20th cycle was determined after SVALGAAKD (1975) and MANSURW cf al. (1976): only
and
ionosphere has become the object of much research in recent years. The effects of the changes in the IMF polarity on the lower ionosphere and, thereby, on the reflection or absorption of radio waves can be considered as proved (SCHLEGELet ul., 1977; OKSMAN and RANTA, 1979; LASTOVICKA, 1979; OKSMAN and RANTA, 1980). The effects of the IMF sectorial structure on the F2-layer are not very clear since they are expected to be obscured by other influences that are more important for this layer. Most papers, dealing with the IMF influence on the F’?-layer, study the effect of the sector boundary crosstng. For example, D’ANGELO (1980) has studied the dependence of FZ-layer critical frequencies on the state of the IMF from the point of view of electrodynamic coupling between high- and lowlatitude regions, and he also notes a decrease of,foF2 during the first day after crossing the sector boundary, Attention to the inffuence of sector boundary crossing on the total electron content and on F2-layer parameters has also been paid by LYON and BHATANGAK(1979), however, the dependence obtained is less pronounced than that found by D’Angelo. The state of the F2-layer on days with different IMF polarities has been studied by SHAPIROand POTAPOVA (1974) and PWAKWA and SHAPIRO (1974). They pointed out that the effecect of the interplanetary magnetic field during magnetically quiet periods can cause day-to-day fluctuations of the ionospheric parameters and strong changes in nighttime heights of the F2-region. In this paper, the results are given of an investigation on IMF effects on the FZ-layer as obtained by evaluating data from thirteen ionospheric stations in the Northern Hemisphere and six in the Southern Hemisphere.
Table I
37
Station
Geographic latitude longitude
Salechard Jakutsk Juliusruh Lindau Prahonice Wakkanai Simferopol Sofia Ebro Akita Kukubunji Yamagdwa Dalhi
66.58”N 62.05”N 54.63 N 51.65’N 49.99“N 45.4VN 44.83’ N 42.70“N 40.81’.N 39.73’N 35.7@ N 31.20’N 28.63’N
66.67”E 129.67”E 13.38”E 10.13”E 14.55’ E 141.6X”E 34.07’ E 23.3S’.E 0.49’ E I40.13”E 139.48”E 130.65&E 77 I27”E I
Townsville Brisbane Canberra Hobart Christchurch Campbell Island
19.10’5 27.53”s 35.32”s 42.92”s 43.57”s 52.55”s
146.50”E 152.92’E 149.00”E 141.17’E 172.80”E 167.15’E
Invariant latitude
61.28’ 55.13 51.67 4X.86 46.15 36.X2 40.52 37.76 37.05 30.25 25.62’ 19.83 15.19 -26.10 - 35.53 -44.86 - 53.60 -49.80 -59.92’
_
1. 4.33 3.06 2.60 2.31 1.13
1.56 1.71 I.60 1.57 1.34 1.23 I.13
I .0x 1.24 1.51 1.99 2.84 2.40 3.98
L. TRis~ovA
38
data for those days, for which the polarity was identical according to both catalogues, were considered. Data published in Sob Geophysical Data (424-Part I, 38, December 1979) were used for the 21st cycle. The selection process described above naturally decreased the volume of data to be examined, and the question arose whether the results obtained would in thesecircumstances have any physical significance. The IMF influence on foF2 is only a secondary effect and for a simple statistical evaluation based on median values it might well be obscured by other factors. Data from two mid-latitude ionosphere stations, Lindau and Prfihonice, which are near to one another, were chosen for the initial investigation. At both stations, the local time dependence offoF is almost identical. Theinitialassumption was that within agiven time period an ,fijF2-deviation on days with different IMF polarity should have the same sense at both stations. This assumption has really been confirmed for the whole period under consideration. An example of results obtained is shown in Fig. 1where the medians of hourly ji)F2-values are plotted against local time. Almost smooth curves are obtained for nighttime hours, whereas the daytime shows larger differences between both stations. In the latter case, the lack of processed data may become important: a sounder
0
6
12
18
11
Fig. 1. Diurnal variation offoF median values with respect to the IMF polarity vs local time. Northern mid-latitude stations : Lindau A = + polarity, A = - polarity: Prahonice l = + polarity, 0 = - polarity.
failure or local interference at one station can cause a considerable shift of the median value compared with the same value from the other station. Despite this, however, the shift in the median values for days with different IMF polarity always shows the same sense and its magnitude is comparable at both stations. Thus it can be assumed that information obtained by simply determining the ,foF2-medians separately for days with positive and negative IMF polarity is of physical significance and can, therefore, be safely used to investigate the influence of the IMF sectorial structure on the F2-layer. RESULTS
From an analysis of the whole period under investigation it is found that in the daytime practically no consistent features can be found for,foF2-values on days with different IMF polarity. For example, at latitude 50”N (stations Lindau and Pruhonice), the medianfoF2-value in 1969 is always higher for days with negative IMF polarity while in 1957 and 1968 this is valid only for March and October, in 1958 only for September, in 1959 for September and October, in 1970 for October, and no such case occurred in 1979. Certain typical features could be found for nighttime hours when the geomagnetic held is the only permanent factor which, together with local electric fields (E W component), affects the critical F2-layer frequency.
11
Fig. 2a. Median nighttime values offoF
with respect to the IMF polarity vs local time. Northern mid-latitude stations: Lindau A = + polarity, A = - polarity; PrShonice 0 = + polarity, 0 = - polarity.
Effects of IMF polarity
35,
on the F2-region I
2
3
4
. 6. 1 :
:
b..
0
.APR l
.O
.
l
0 0 .
0
”
OCTY o.
b
Fig. 2b. Median nighttime values offoF with respect to the IMF polarity vs local time. Southern mid-latitude station: Hobart 0 = + polarity, 0 = - polarity.
Fig. 3. Values of the representative factor B calculated from definition (1) vs L-parameter: l = data for the year 1958, x = data for the year 1969.
At both northern and southern mid-latitudes, smaller medianfoF2-values were found in March and April for days with negative IMF polarity, whereas in September and October higher values occurred for days with negative polarity. An example of the.foF2 variation with local time is shown in Fig. 2 where results of the analysis of data from Lindau, Prdhonice and Hobart are given for equinoxial periods of the 19th, 20th and 21 st solar cycle maxima. In order to make a comparison of the results from different stations possible, a representative factor
variation of the B-factor as derived from Lindau and Juliusruh (data measured during 1958 in the maximum ofthe 19th solar cycle) and corresponding K-indices for days with negative IMF polarity.
XI”
B=---
-cf-.+
* 100
Cf
was introduced wherej ’ is the medianfoF2-value for days with positive IMF polarity in a given month,fis the same for days with negative polarity. The sum includes hourly values between 22 and 06 hours local time. A positive value of B thus represents higher critical FZ-layer frequencies on days with positive IMF polarity. Values of the B-factor for the individual months are plotted in Fig. 3 vs L-values corresponding to the stations listed in Table 1. It will be seen that the phenomenon shown in Fig. 2 (lower critical frequencies on days with negative IM F polarity in March and April and higher in September and October) is true for practically all the stations studied in this analysis. For the sake ofcompleteness, Fig. 4 shows the annual
DISCUSSION
For the circumstances described above (the use of simple medians, low number of values), the B-factor as defined in the preceding section has to be considered as a rather qualitative index. Nevertheless, the results shown in Figs 2,3,4 suggest some general conclusions. The phenomenon established herein, i.e. that nighttimeSoF on days with negative IMF polarity are lower in March and April and higher in September and October than on days with positive IMP polarity can be considered an objective fact. This is a planetary phenomenon appearing equally in both hemispheres over a considerable range of latitudes, and it is in accordance with investigations of the dependence of geomagnetic field changes on the IMF polarity. It is also in accordance, for example, with Fig. 1 in D’ANGELO’S paper (1980) where average values offoF from Lindau and Dourbes are plotted for 00-03 hours LT for every day of the period 1 April to 31 December 1974. The disagreement with this conclusion for some results (from stations with geographic longitudes
40
Fig. 4. Annual variation of the factor B m 195X and average K-indices l’or days with negative IMF polarity: = Lindau, ---- = Juliusruh (lack of data in May), x = K,, 0 = K-index measured at the Prilhonice station, l = K’( = average K-index calculated for night hours only).
exceeding 130’E) could be expiained by a possible inaccurate coordination of the IMF polarity to individual days since the day polarities as given in the catalogues used, refer to the zero meridian, or by exceptional local magnetic activity in the given region. Taking into account the fact that the average critical F2-layer frequencies decrease on days of enhanced geomagnetic activity (effect of the negative phase of geomagnetic storms), this phenomenon confirms the annual variation of geomagnetic activity with two maxima in the equinoxial periods as well as their distribution according to IMF polarity (R~sstit and M~PHERRON, 1973; BUNCH, 1973; B~~~~~ELI~K,1975). For example, the planetary Am-index shows two maxima in its annual variation at the equinoxial periods, attaining for days with negative IMF polarity (direction towards the Sun) maximum values only in the first half and for days with positive polarity only in the second half of the year. The annual varjation of the aurora1 Ah-index shows one maximum, but two maxima appear at the equinoxial periods when thedays aredividedas to their IMF~~~~~~~~(BEKTwELIER,1976). The annual variation of the B-factor (Fig. 4) is also in qualitative accordance with the annual variation of geomagnetic activity on days with negative IMF polarity as given in the papers referred to above. At the same time the changes in the B-factor reflect the nature of changes in geomagnetic activity on days with negative IMF polarity since, with increasing geomag-
netic activity on these days, 3 increases as a result of the decreasing sum C,f -- in definition (I). Differences in ,ji)F2 on days with different IMF polarity tend to be larger at larger geomagnetic latitudes. For most of the stations investigated here with L > 2, this dilIerence is 1tr-ZSl?;,. The above results refer to the maximum periods of the 19th, 20th and 2lst solar cycles. A similar analysis made for the period of solar minimum (1964) did not yield an unambiguous result.
From the results presented here it can be suggested that the effect of the sectorial structure of the IMF appears in the F2-region as a response to changes in geomagnetic activity caused by the changes of the IMF polarity. It is really observable only during nighttime hours since it is obscured by other factors during the daytime. This phenomenon is most pronounced in equinoxial periods at solar maximum. It is effective in both hemispheres in that average nighttime ,fiFZvalues are lower on days with negative IMF polarity in March and April, and higher in September and October thanondayswithpositi~~eIMFpolarity.In therangeof invariant latitudes of 45-66 the magnitude of this difference reaches about 202, and even more in the period under investigation. and it shows an increasing trend with increasing geomagnetic latitude.
REFERENCE BERTHELIEKA. BERTWELIER A.
1975 1976
BURCHJ. L.
1973
D’ANC;ELO N. LASTOVI?KA J. LYON G. F. and BHATANGAR V. P. MANSIJROV S. M., MANSUROV G. S. and M~NSUUO~A
1980 1979
L. G.
I979 1976
CT.r. Acud. Sci., Ser. B 280, J. geophys. Rex 81, 4546. J. geophys. Res. 78, 1047. Can. J. Phys. 58, 693.
195.
J. atmos. terr. Phys. 41, 995. Can. J. Phys. 57, 21X. ‘~nturktika 15, 16.
Effects of IMF polarity J. and RANTA H. J. and RANTA H. RUSSE:L.L C. T. and MCPHEKKON R. L. POTAPOVAN. I. and SHAPIKO B. S. S~HLIXXL K.. ROSE G. and WIUDEL H. U. SHA~IKO B. S. and P~TAP~VA N. 1. SVMX \*Iw I_ OKSMAN OKSMAN
1979 1980 I973 1974 1977 1974 1975
on the F2-region IAGA Bullerin 43, 311. Planet. Space Sci. 28, I I55 J. geophys. Rex 78, 92. Gromagn. Aeron. 14, I 101. ./. utwx [err. Phys. 39, 101. Guomagn. Aeron. 14, 1099. SUIPR Report No. 629, Institute for Plasma Stanford University, Stanford, California.
41
Research,