Abstract
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<EM> f</EM> = <EM>E</EM><SUB>sw</SUB><EM>P</EM><SUB>sw</SUB><EM>M</EM><SUB>A</SUB><sup>-1/2</sup> (<EM>E</EM><SUB>sw</SUB>, <EM>P</EM><SUB>sw</SUB>, and <EM>M</EM><SUB>A</SUB> 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 <EM>f.</EM> (3) The reconnection voltage is approximately fitted by sin<sup>3/2</sup><EM>θ</EM><SUB>IMF</SUB>/2, where <EM>θ</EM><SUB>IMF</SUB> 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 <EM>θ</EM><SUB>IMF</SUB>, so it is not justified to take them as substitutes for the reconnection voltage.
Highlights
In the Solar Wind-Magnetosphere-Ionosphere (SMI) system, one question of most interest is the energy transfer and the transformation between mechanical and magnetic energies
(2) In terms of more than 100 simulation runs with due southward Interplanetary Magnetic Field (IMF), we have found a combined parameter f = EswPswMA−1/2 (Esw, Psw, and MA 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 sin3/2(θIMF/2), where θIMF is the IMF clock angle
Quantitative analyses of the electric current and electric field based on global MHD simulation data will greatly promote our understanding of the electrodynamic coupling in the Solar Wind-MagnetosphereIonosphere (SMI) system
Summary
In the Solar Wind-Magnetosphere-Ionosphere (SMI) system, one question of most interest is the energy transfer and the transformation between mechanical and magnetic energies. The former involves and the latter entirely belongs to electrodynamic processes. A quantitative investigation of the electric field and current heavily relies on global MHD simulations of the SMI system. Our review contains 3 aspects: the bow shock contributions to the region 1 Field-Aligned Current (FAC) and the crosstail current, the saturation of the ionospheric transpolar potential and the magnetopause reconnection voltage, and the reconnection voltage versus Interplanetary Magnetic Field (IMF) clock angle (the angle between the IMF and the z-axis), covered by the following 3 successive sections in proper order.
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