Electromagnetic Energy Transfer across the Magnetopause

A three-dimensional adaptive magnetohydrodynamic(MHD) model is used to examine the electromagnetic energy flow from the solar wind to the magnetosphere.The magnetopause is determined by finding approximately the inner edge of the void encompassed by the solar wind stream lines,and the magnetopause is divided into nightside and dayside part by polar cusp region.This study found that the magnetopause energy transfer has close relations with solar wind conditions.The magnetopause area also effects energy transfer.For northward IMF,most of the electromagnetic energy flux inflow occurs near the polar cusps on magnetopause;for southward IMF the largest electromagnetic energy input into the magnetosphere occurs at the tail lobe behind the cusps.Under southward IMF conditions,more electromagnetic energy input can be identified as increasing solar wind density while it does not enhance as much for northward IMF.Our results suggest that the mechanisms proposed to electromagnetic energy transfer are mainly due to reconnection.If the electromagnetic energy coupling between the solar wind and the magnetosphere can be interpreted as a proxy for the reconnection efficiency,the efficiency during northward IMF is about 10%~30%of that for southward IMF under the solar wind conditions we considered.