Numerical Study on Dynamics and Polarization of the Hot Plasma Torus in the Magnetosphere : Cause of Generation of the Paired Region 1 and Region 2 Field-Aligned Currents

Abstract

To begin with, we postulate that in the magnetosphere, the hot (≥1 keV) plasma particles are primarily distributed in a magnetic shell which is connected to two ovals of diffuse auroras on the northern and southern polar ionospheres. Such hot plasma population is called the hot plasma torus (HPT). To study dynamics and polarization of the HPT in the magnetosphere, we perform the two-dimensional numerical simulations which is capable of treating the electrostatic coupling between the magnetosphere and the ionosphere. The simulation results show that distortion of the HPT occurs due to the solar wind convection when the interplanetary magnetic field (IMF) is southward, so that the polarization of the distorted HPT produces a pair of the region and region 2 field-aligned currents (FACs) which agrees with the observations. It is also shown that the self-distortion of the HPT (positive feedback) is possible; namely, the HPT is further polarized by electric fields arising from the polarized HPT, which leads to intensification of the region 1/region 2 FACs. Notably, in our model the disruption of a tail current is a natural result of the HPT distortion on the nightside, which can explain the observations that the tail current disruption occurs over a wide MLT range and well inside the magnetically closed region.