Three-dimensional magnetohydrodynamic simulations on the interaction of interplanetary density pulses with the bow shock

Abstract

Three-dimensional magnetohydrodynamic (MHD) simulations are carried out in order to study the interaction of upstream density pulses with the planetary bow shock. In this work, three distinguished types of the density pulse have been simulated: (1) Pure density pulse with no variations in all other variables, (2) density pulse in fast/slow mode-like type, and (3) another pure density pulse with a much stronger peak. For the first case, where the peak density is two times the background value, its interaction with the bow shock results in various MHD waves and a shock in the magnetosheath, including the fast mode wave which evolves into a fast shock, the entropy wave, and the slow mode wave. For the second case, the amplitude of the transmitted density pulse in the magnetosheath is reduced overall as compared to that in the first case. This is due to the generation of the stronger fast mode wave in the magnetosheath, and the effect is more pronounced for the fast mode-like pulse than for the slow mode-like pulse. When the third type pulse is incident with the peak density being five times the background value, the magnetosheath is more strongly compressed, which is followed by an expansion due to the sunward repulsion and then a second compression again. This still results in similar MHD waves and a shock in the magnetosheath, but they are generated in manners well-distinguished from the previous two cases. Based on the results from all three cases, it is suggested that the density amplitude and the properties of its related waves/shock in the magnetosheath can appear quite different depending on the observing spacecraft's position, and thus necessitating a multispacecraft measurement for a reliable monitor. (C) 2002 American Institute of Physics.