Energy Transfer Across the Magnetopause Under Radial IMF Conditions

Abstract

A global MHD model is used to study the energy transfer from solar wind to magnetosphere through magnetopause under radial interplanetary magnetic fields (IMFs). We use the streamline method to determine the smooth surface of the magnetopause by searching the inner boundary of the solar-wind streamline and discuss the roles of magnetic reconnection and viscous interaction under radial IMFs, which we compare with cases of north-south IMFs. We find that (1) the energy transfer across the magnetopause is asymmetric between the northern and southern hemispheres due to different reconnection locations, particularly for electromagnetic energy; (2) for sunward IMF, the most significant area of the net input of mechanical energy occurs on the day side and near-Earth magnetotail, and the electromagnetic energy input in the northern hemisphere is much larger than in the southern hemisphere on the night side; (3) the mechanical and electromagnetic energy-transfer distribution in the northern (southern) hemisphere for earthward IMF is the same as that in the southern (northern) hemisphere for sunward IMF; (4) the electromagnetic energy input for radial IMF is two times larger than for northward IMF, but three times smaller than for southward IMF, the viscous effect is smaller than for northward IMF but comparable to that for southward IMF, the rate of energy transfer is 2.22% for radial IMF, which is lower than 4.95% for southward IMF, but higher than 1.7% for northward IMF; and (5) the Akasofu-type energy-coupling formula, epsilon, is not suitable for the solar-wind events dominated by IMF B ( x ).