Mars' Dayside Induced Magnetosphere Under Quasi-Radial Interplanetary Magnetic Field—A MHD Model Study

Abstract

The interplanetary magnetic field (IMF) is one of the important external drivers that control the Martian plasma environment. There is some controversy about the characteristics of the Martian plasma environment under radial IMF conditions. Utilizing a three-dimensional magnetohydrodynamic (MHD) model, this study analyzes the impact of IMF cone angle on the electromagnetic field and ion motions in Martian space, and investigates the Martian space environment under radial IMF conditions. Simulation results indicate that the decrease in IMF cone angle weakens the electromagnetic fields. The reduction in magnetic field pile-up leads to a weakened induced magnetosphere. Therefore, solar wind protons experience less deceleration and deflection across the bow shock (BS), which is compressed to lower altitudes. Under radial IMF, though the electric fields that impede the penetration of solar wind particles are weak on the dayside, the BS, the magnetosheath, and the induced magnetosphere structure can still form, and the pile-up of magnetic fields can still be observed. In contrast to previous reports of BS disappearance under radial IMF, our simulations show that a BS and a structured magnetosheath persist even at extremely small cone angles. These results help reconcile conflicting observations and provide constraints for interpreting MAVEN measurements during near-radial IMF intervals.