Energy Flow in the Region 2 Field‐Aligned Current Region Under Quasi‐steady Convection

Abstract

We investigated energy flow in the inner magnetosphere on the basis of the results obtained by a global magnetohydrodynamic simulation. When the magnetosphere is exposed to a southward interplanetary magnetic field, the magnetosphere undergoes quasi-steady convection. Downward (earthward) Poynting flux is found in the polar cap, which is consistent with previous observations. However, Poynting flux appears to be upward (antiearthward) in the equatorward region of the auroral oval. The Region 2 field-aligned current (FAC) is embedded in the upward Poynting flux region. The upward Poynting flux is closely associated with space charge deposited by the ionospheric Hall current under inhomogeneous ionospheric conductivity. The space charge gives rise to shear flow of plasma, which is transmitted upward to the magnetosphere. The shear flow generates additional Region 2 FAC, at least, in the low-altitude magnetosphere. Spatial distribution of the Region 2 FAC appears to depend on altitude, suggesting the significant influence of the ionosphere in the Region 2 FAC region. We traced integral curves of Poynting flux (S curves) backward from a magnetic field line in the Region 2 FAC region and found that the S curves originate either in the solar wind and in the earthward-most boundary of the simulation. These simulation results suggest that the ionosphere participates in the generation of the Region 2 FAC, and the ionosphere is a mediator to feed energy to the inner magnetosphere under the quasi-steady convection.