Foreshock wave interaction with the magnetopause: Signatures of mode conversion

Abstract

Our previous hybrid simulation (Shi et al., 2013) under a radial interplanetary magnetic field (IMF) and a supercritical solar wind Mach number has shown that foreshock compressional waves originated from the quasi-parallel (Q-parallel to) shock are mode converted to kinetic Alfven waves (KAWs) at the Alfven resonance surface of the subsolar magnetopause. In this paper, three-dimensional global dayside mode conversion is investigated for cases under various solar wind conditions using the global hybrid model. The global patterns and propagations of KAWs are distinguished and presented. Under a near-critical Mach number (M-A = 3), KAW structures due to mode conversion exhibit a feature of broader excitation regions in the magnetopause boundary layer (MPBL) compared to supercritical Mach number (M-A = 5) shocks. For cases with an oblique IMF with supercritical Mach numbers (M-A = 5), the amplitude of magnetosheath compressional waves is larger at the quasi-parallel shock (Q-parallel to) than at the quasi-perpendicular (Q-perpendicular to) shock. Downstream of the Q-parallel to shock, there is a general trend that the perturbations of density (N) and magnetic field (B) change from predominantly in-phase in the magnetosheath to antiphase near the MPBL. While downstream of the Q-perpendicular to shock, an antiphase relation between N and B is dominant throughout the magnetosheath and magnetopause except near the shock transition. The compressional drivers are found to reach an extended region of the magnetopause due to the combined effects of wave propagation in the plasma frame and flow convection, leading to a broad region of mode conversion at the magnetopause. Subsequently, the resulting KAWs can be carried to the regions downstream of the Q-perpendicular to shock owing to the flow convection at the magnetopause. The KAWs propagate poleward along the geomagnetic field lines and meanwhile are carried tailward by the ambient flows, and they are more intense in the downstream of Q-parallel to shocks than downstream of Q-perpendicular to shocks.