Electrodynamic coupling in the solar wind-magnetosphere-ionosphere system

This paper presents a brief summary of our recent work based on global MHD simulations of the Solar wind-Magnetosphere-Ionosphere (SMI) system with emphasis on the electrodynamic coupling in the system. The main conclusions obtained are summarized as follows. (1) As a main dynamo of the SMI system, the bow shock contributes to both region 1 Field-Aligned Current (FAC) and cross-tail current. Under strong interplanetary driving conditions and moderate Alfven Mach numbers, the bow shock's contribution may exceed more than fifty percent of the total of either region 1 or cross-tail currents. (2) In terms of more than 100 simulation runs with due southward Interplanetary Magnetic Field (IMF), we have found a combined parameter f = EswPswM − 1/2 A (Esw, Psw ,a ndMA are the solar wind electric field, ram pressure, and Alfven Mach number, respectively): both the ionospheric transpolar potential and the magnetopause reconnection voltage vary linearly with f for small f , but saturate for large f .( 3) The reconnection voltage is approximately fitted by sin 3/2 (θIMF/2), where θIMF is the IMF clock angle. The ionospheric transpolar potential, the voltage along the polar cap boundary, and the electric fields along the merging line however defined they may be, respond differently to θIMF, so it is not justified to take them as substitutes for the reconnection voltage. Keywords Earth's magnetosphere, Ionosphere, Electrodynamic coupling, Numerical simulation