Impact of Solar Wind Density and Velocity Variations on the Martian Magnetosphere and Ion Escape Process

The dynamic pressure of solar wind, which is determined by both solar wind density and velocity, is a crucial factor influencing the Martian plasma environment. In this study, we employ a multifluid magnetohydrodynamic (MHD) model to investigate the distinct effects of variations in solar wind velocity and density on boundary layers and the ion escape process. The simulation results indicate that, when the solar wind dynamic pressure is held constant, an increase in solar wind density leads to a significant expansion of the bow shock (BS) and a slight contraction of the magnetic pile-up boundary. Under conditions of elevated solar wind density, the electric fields that typically inhibit solar wind penetration weaken, allowing a greater number of solar wind protons to traverse the BS. This results in enhanced energy inputs, leading to increased thermal and magnetic pressures. Consequently, the tailward ion escape flux rises substantially due to the increased planetary ion density associated with the higher solar wind proton density. Furthermore, under these conditions, the magnetic field lines exhibit greater piling-up, with the interplanetary magnetic field penetrating to lower altitudes within the ionosphere, thereby creating additional tailward transport channels for planetary ions. Additionally, as solar wind density increases, the current sheet shifts toward the dawn side, resulting in a more pronounced asymmetry structure.