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

Abstract

We performed a series of global MHD simulations to study the closure of the cross-tail current in the magnetotail under different solar wind conditions. The cross-tail current closes totally within the magnetopause, forming the classical θ structure when IMF is set to be zero. The situation changes for southward IMF cases: part of the cross-tail current passes through the magnetosheath and closes across the bow shock, forming an overlapped θ structure of the cross-tail current, when viewed from the Sun. Quantitative analysis shows that a larger strength of the southward IMF BZ results in a higher percentage of current closed through the bow shock. Nearly a constant quantity of the cross-tail current comes from the bow shock despite variations in the solar wind speed. An increase in the ionospheric Pedersen conductance leads to an increase in the bow shock contribution but a decrease in the magnetopause contribution to the cross-tail current; therefore, the net cross-tail current is almost independent of the ionospheric conductance. Cross-tail current that closes across the bow shock rather than the magnetopause can be classified as the magnetic reconnection current, providing energy supply for dissipation needed at the magnetic reconnection region in the magnetotail. Copyright 2009 by the American Geophysical Union.