Simulation and comparison of particles entering the plasma sheet under northward and southward IMF conditions

Abstract

Using a newly modified global magnetohydrodynamics (MHD) simulation model and test-particle method, we investigated the mechanism of plasma transfer into the near-tail plasma sheet under different interplanetary magnetic field (IMF) conditions (northward and southward). The results explain some well-known observations and clearly reveal the physical nature of the plasma transfer: particles mainly originate from the solar wind under a northward IMF and from the Earth under a southward IMF. We found solar wind particles transfer into the plasma sheet through dusk and dawn flanks under a northward IMF, and the transfer paths are consistent with merging sites on the magnetopause. When the IMF is southward, the solar-wind plasma transferring into the plasma sheet is mainly from the northern and southern sides. The average energy of the injected ions is much higher when the IMF is southward, which would result in a shorter stay-time in the plasma sheet. The tail terrestrial magnetic field lines are more open in the north-south direction when the IMF is southward, and this pattern makes it easier for terrestrial particles with higher energies to be ejected into the plasma sheet.