Simulation of ion velocity distributions in the magnetosheath

Abstract

A two‐dimensional global hybrid simulation is carried out to study the ion velocity distributions in the dayside magnetosheath in the presence of a northward interplanetary magnetic field. In the simulation, the bow shock and the magnetosheath form self‐consistently by the interaction between the solar wind and the geomagnetic field. Downstream of the quasi‐perpendicular shock, the initial isotropic distribution of upstream ions first becomes an oval‐shaped bi‐Maxwellian distribution with the perpendicular temperature T⟂ greater than the parallel temperature T∥. These downstream ions are then found to evolve to a conic‐like or D‐shaped distribution in the high‐latitude magnetosheath prior to the transmission into the magnetosphere. The presence of the D‐shaped distribution is due to the adiabatic ion motion from the subsolar magnetosheath with a high magnetic field strength to high latitudes with a lower field, but not due to magnetic reconnection at the high‐latitude magnetopause.