The influence of external solar-wind drivers on the physical characteristics of the Martian bow shock

Abstract

The Martian bow shock represents the main interface between the upstream interplanetary space and the downstream planetary obstacle, where the solar-wind plasma and the frozen-in interplanetary magnetic field (IMF) begin to be perturbed. However, the physical characteristics of the Martian bow shock layer and the influence of the external solar wind drivers on them remain unclear. By employing a three-dimensional Hall magneto-hydrodynamic (MHD) model, this study aims to reveal the physical characteristics of the Martian bow-shock layer extracted from the maximum radially inward gradient of the solar-wind velocity (V_{S W), including the magnetic field, current density, electric fields, and the energy transfer between the fields and solar wind protons, as well as the influence of the VS W and the IMF on these features. Simulation results indicate that the IMF has initiated the processes of piling-up, draping, bending, and slipping at the Martian bow shock, inducing an associate current to flow from the +ZMS E pole to the −ZMS E pole along the bow-shock layer, with the strongest being located at the subsolar position. Furthermore, the total electric field at the Martian bow shock is constituted by the motional electric field (EM) with the +ZMS E direction around the ±ZMS E flanks and the outward ambipolar (EA) and Hall (EH) electric fields around the lower solar zenith angles; through these, the solar wind transfers its kinetic energy to the electromagnetic fields. A higher VS W gives rise to an enhanced magnetic field, current density, and electric fields at the Martian bow shock, thereby leading to an increase in the corresponding energy-transfer rates. A greater magnitude of the IMF cross-flow component tends to result in an intensified magnetic field, current densities, EM, and EH; while it causes a decreased EA and associated energy-transfer rate at the bow shock layer. If the Parker spiral angle of the IMF is not restricted to 90°, a portion of the quasi-parallel bow-shock layer will be formed, within which the magnitudes of the magnetic field, current density, EH, and the corresponding energy-transfer rate through EH are all lower than those of the quasi-perpendicular bow-shock layer. The results of this study provide valuable insights into the physical properties at the bow-shock layer that emerge during the Mars-solar-wind interactions.}