Study on the interaction of interplanetary disturbances with the magnetosheath

Abstract

Three dimensional magnetohydrodynamic (MHD) simulations are carried out in order to study the interaction of various interplanetary disturbances with the planetary bow shock. In this study, 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. In 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, entropy wave, and slow mode wave. In 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. Also, it was found that the generated fast mode wave communicates the effect of the incident density pulses on the magnetopause faster than the speed of the disturbances. When the third type pulse is incident with the peak density being 5 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 results in similar MHD waves and a shock in the mangetosheath, 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 require a multi-spacecraft measurement for a reliable monitor. We have also performed MHD simulations to study the interaction between three well-known MHD wav...