Dynamics of field-aligned currents in two hemispheres during a magnetospheric storm from magnetogram inversion technique data

Abstract

We continue to study the physical processes occurring during the August 17, 2001 magnetospheric storm by analyzing the dynamics of the intensity of field-aligned currents (FACs) in Iijima—Potemra Region 1 in the polar ionospheres of the two hemispheres, using the modernized magnetogram inversion technique. The results obtained on the dynamics of two types of FAC asymmetry (dawn-dusk and interhemispheric), as well as the previously obtained regularities in the behavior of Hall currents and the polar cap boundaries depending on the large azimuthal component of the interplanetary magnetic field (IMF), observed during the storm, and the seasonal behavior of the conductivity are consistent with the open magnetosphere model and with satellite observations of auroras in two hemispheres. We have shown that the weakening of the asymmetry of two types in the FAC distribution during substorms in the storm under study occurs almost completely in the winter hemisphere and is much weaker in the summer one. We associate this phenomenon with the predominance of the effect of long-term exposure to the azimuthal IMF component in the sunlit polar ionosphere of the summer hemisphere over the substorm symmetrization effect of the night magnetosphere. A symmetrization effect of the polar cap and FACs, created by the solar wind pressure pulse at the end of the storm, is observed. We propose a qualitative explanation of this effect.

Universal Time variations in the magnetosphere

“…It is possible to devise many scenarios and causes for these relationships between the FACs but identifying definitively the causes is almost certainly going to require the use of a global MHD model of the coupled magnetosphere-ionosphere system with an eccentric dipole field model. Of relevance here are the findings of Mishin et al (2021) who analysed FACs derived from magnetogram inversion techniques and of Coxon et al (2016) from AMPERE results. These authors shown that R1 FAC intensities in the summer hemisphere exceed those in the winter hemisphere, indicating a conductivity effect that also induces a UT variation; Coxon et al (2016) find an almost sinusoidal diurnal dependence of total FAC intensities in one hemisphere (R1 and R2 and dawn and dusk) whereas we see more complex semi-diurnal variations when we divide the data by R1 or R2 regions and by dawn or dusk.…”

“…Coxon et al (2016) also conclude that the total FAC current intensities are set by a combination of the magnetic flux throughput in the ECPC model and the polar conductivities. Mishin et al (2021) report the sense of the inequality between FAC intensities in the dawn and dusk sectors was also shown to be different in the Northern and Southern Hemispheres which Mishin et al (2021) attribute to an IMF [B Y ] GSEQ effect. This dawn-dusk asymmetry decreased with increasing substorm activity and almost completely disappeared in the winter hemisphere.…”