G. A. Kotova

Analytical model of the near-Earth magnetopause according to the data of the Prognoz and Interball satellite data

Based on the magnetopause observations near the Earth by the Prognoz/Interball satellites in 1972–2000, the empirical model of this boundary has been proposed, and the magnetopause behavior at different parameters of the oncoming solar wind has been studied. For the first time, it has been detected that the Earth’s magnetopause is compressed by ∼5% in the direction perpendicular to the plane including the vectors of the solar wind velocity and IMF. At the same time, any dependence of the subsolar magnetopause position on the IMF Bz component has not been revealed in the Progrnoz/Interball data. The proposed magnetopause model can be used to model the position and shape of the near-Earth bow shock.

Dynamics of the plasmasphere and plasmapause under the action of geomagnetic storms

Number density and temperature of cold H+ ion fluxes in the plasmasphere measured by the Auroral probe/Alpha 3 experiment during two geomagnetic storms are analyzed. It was found that after the onset of geomagnetic storms the plasmapause both on the night and day sides starts moving toward the Earth almost simultaneously. The delay of the beginning of plasmapause movement on the day side relative to the night side is at least much less than the corotation time of magnetic tube with cold plasma from the night sector into the day sector of the plasmasphere. It was found that the number density of cold plasma inside the daytime plasmasphere could significantly change, either decrease or increase, during moderate geomagnetic storms. Now we cannot definitely determine the reason for these variations, but we assume they are caused by variations of parameters (e.g., nmaxF2,hmaxF2) in the underlying ionosphere initiated by geomagnetic storms.

Dynamics of Temperature and Density of Cold Protons of the Earth's Plasmasphere Measured by the Auroral Probe/Alpha-3 Experiment Data during Geomagnetic Disturbances

We present the results of temperature and density measurement of plasmaspheric protons under quiet and disturbed conditions in the night and dayside sectors of the plasmasphere obtained with the Auroral Probe/Alpha-3 instrument during September 1996 and January 1997. According to the experimental data, the proton temperature in the night sector of the plasmasphere depends on the level of geomagnetic disturbance: it is found that at night hours the values of temperatures inside the plasmasphere at 2.4 < L < 3.5 decreased considerably after the commencement of a geomagnetic storm. The temperature decrease, as a rule, was accompanied by the formation of a flat plateau on the density distribution n(L) at 2.4 < L < 3.5. The above experimental facts (decreasing proton temperature and formation of a flat part on the n(L) distribution) allow us to conclude that the decrease in the proton temperature in the night sector of the plasmasphere connected with magnetic disturbances is caused by the filling of field tubes (depleted after the commencement of the storm) with colder ionospheric plasma. The proton temperature in the dayside sector of the plasmasphere virtually does not depend on the level of the geomagnetic disturbance.

Restoration of the proton density distribution in the Earth’s plasmasphere from measurements along the INTERBALL-1 satellite orbit

Based on experimental data obtained in 1995–2000 on board the INTERBALL-1 spacecraft using the ALPHA-3 instrument, a semi-empirical two-dimensional model of the Earth plasmasphere is developed, which allows for the plasma distribution in the entire meridional plane to be restored from the temperature and proton density measurements along the satellite orbit. The model has also been tested using the data of the IMAGE spacecraft. The model uses theoretical expressions (Lemaire and Schere, 1974) that describe the plasma distribution in the plasmasphere for the cases of thermal equilibrium and collisionless initial partial filling of plasmaspheric shells; therefore, the parameters of the constructed model have a clear physical meaning and make it possible, in particular, to estimate the degree of plasmasphere filling.

Position variations of the polarization jet and injection boundary of energetic ions during substorms

The comparison of selected cases of polarization jet observation at ground stations and measurements of energetic ions at the AMPTE/CCE satellite shows that these phenomena occur simultaneously and on the same L shells. Polarization jet observations at DMSP satellites make it possible to statistically determine the dependence of its equatorial boundary position on the AE-index value. It is also shown that, in the case of isolated magnetic disturbances, the position of the inner boundary of injection of energetic ions measured at the AMPTE/CCE satellite depends on the AE index. It was found that the dependences of both boundaries on the AE index match over a wide range of AE variations. This is evidence that the equatorial boundary polarization jet band and the inner boundary of the injection of energetic ions are physically interconnected and are formed on the same L shells during substorms.

Study of notches in the Earth’s plasmasphere based on data of the MAGION-5 satellite

Depleted narrow (localized in longitude) regions (field tubes) in the plasmasphere, recently discovered in He+ radiation measurements on the IMAGE spacecraft, were first directly observed by the Magion-5 satellite. The low-density regions (notches) occupy <∼ 10–30° in longitude and extend from L ∼ 2–3 to the plasmasphere boundary in neighboring plasmasphere regions with larger densities. The Magion-5 data give evidence that in the low-density regions temperature is enhanced as compared to the neighboring denser plasmasphere regions. Formation of notches in the plasmasphere is, apparently, associated with AE intensification during weak magnetic storms, while strong magnetic storms usually result in the overall reduction of plasmasphere dimensions. However, even a strong magnetic storm on April 6–7, 2000 (max Kp = 9-and min Dst ∼ −290 nT), but accompanied by an isolated AE impulse, resulted in a density decrease only in the longitudinally limited post-midnight sector of the plasmasphere.

Use of the physically based modeling to choose an adequate method for determining the plasmapause position

From the data on the cold plasma measurements onboard the INTERBALL-1 spacecraft (1995–2000), the plasmapause positions determined from the most frequently used formal criterion—a fivefold or higher decrease in plasma density with an increase in the L-shell by 0.5—and visually from the measured energy spectra of thermal protons have been analyzed and compared. The difference in the results of the both empiric techniques makes it possible to estimate the thickness of the boundary layer of the plasmasphere. The model of the Earth’s plasmasphere developed earlier by the authors (Verigin et al., 2012; Kotova et al., 2015) based on the theoretical expressions makes it possible to reconstruct the plasma distribution throughout the plasmasphere from the measurements along a single pass of the orbiter and to find the plasmapause position defined as the last closed stream line. Comparison of the plasmapause position obtained with empirical techniques to the position of this boundary calculated with physically based models of the plasma distribution in the plasmasphere has shown that the modeled position of the plasmapause approximately coincides with that determined from the formal criterion described above.

Observations of large-scale plasma convection in the magnetosphere with respect to the geomagnetic activity level

The data of the ionospheric observations (the daily f plots) at the Yakutsk meridional chain of ionosondes (Yakutsk–Zhigansk–Batagai–Tixie Bay) with sharp decreases (breaks) in the critical frequency of the regular ionospheric F2 layer (foF2) are considered. The data for 1968–1983 were analyzed, and the statistics of the foF2 break observations, which indicate that these breaks are mainly registered in equinoctial months and in afternoon and evening hours under moderately disturbed geomagnetic conditions, are presented. Calculations performed using the prognostic model of the high-latitude ionosphere indicate that the critical frequency break position coincides with the equatorial boundary of large-scale plasma convection in the dusk MLT sector.

Longitudinal dependence of the H + concentration distribution in the plasmasphere according to INTERBALL-1 satellite data

The paper has presented a study of the dependence of the H+ ions concentration in the plasmasphere on geographic longitude. A vast database of measurements of the cold plasma density by the Alpha-3 instrument on board the INTERBALL-1 satellite has been used for the study. Based on these measurements, a dependence of the H+ ions concentration in the filled magnetic flux tube in the plasmasphere in the equatorial plane under quiet geomagnetic conditions has been obtained as a function of geographic longitude. Studies have been performed for two seasons, summer and winter. It has been shown that, during the summer in the near-midnight sector, the minimum in the H+ concentration falls within geographic longitudes of 270°–315°. The ratio of the concentration of H+ ions at various longitudes could reach a factor of three. During the winter, in the near-noon sector, the maximum of the H+ ions concentration falls within longitudes of 180°–225°, whereas the concentration ratio could reach a factor of 2.2.

Vertical plasma drift velocities in the polarization jet observation by ground Doppler measurements and driftmeters on DMSP satellites

Vertical and horizontal plasma drifts are investigated during the polarization jet (PJ) detection in the F2 ionospheric layer based on the Doppler measurements at the Yakutsk meridian chain of subauroral ionospheric stations. It is shown that the velocities of vertical and horizontal drifts are significantly higher than the background motion during PJ observation periods. The ionospheric plasma motion direction changes from upward to downward on the polar edge of the main ionospheric trough. Doppler measurements on the DPS-4 ionosondes are compared with the simultaneous measurements of the plasma drift on the DMSP satellites during their passage near the Yakutsk meridian. The two kinds of measurements are in good agreement with each other. During the magnetic storm of June 23, 2005, by measurements of the DMSP satellites, the velocities of upward plasma flows were 1.0–1.4 km/s at a satellite altitude of 850 km. In the ionospheric F region, this speed corresponds to 150 m/s. According to satellite measurements, the westward drift velocity reached 2.5 km/s. The development of the polarization jet in the ionosphere was accompanied by a tenfold decrease in the electron density in 15–30 min.