Bow shock and magnetopause contributions to the cross-tail currentfrom global MHD simulations

摘要

We performed a series of global MHD simulations to study the closure of the cross-tailcurrent in the magnetotail under different solar wind conditions. The cross-tail current closestotally within the magnetopause, forming the classical 9 structure when IMF is set to bezero. The situation changes for southward IMF cases: part of the cross-tail current passesthrough the magnetosheath and closes across the bow shock, forming an overlapped 9structure of the cross-tail current, when viewed from the Sun. Quantitative analysis showsthat a larger strength of the southward IMF Bz results in a higher percentage of currentclosed through the bow shock. Nearly a constant quantity of the cross-tail current comesfrom the bow shock despite variations in the solar wind speed. An increase in the ionosphericPedersen conductance leads to an increase in the bow shock contribution but a decrease in themagnetopause contribution to the cross-tail current; therefore, the net cross-tail current isalmost independent of the ionospheric conductance. Cross-tail current that closes across thebow shock rather than the magnetopause can be classified as the magnetic reconnectioncurrent, providing energy supply for dissipation needed at the magnetic reconnection regionin the magnetotail.