Bow shock and magnetopause contributions to the magnetospheric current system: Hints from the Cluster observations

Abstract

We perform a statistical study of the surface current at the high-latitude magnetopause (HLMP) and the bow shock under different southward interplanetary magnetic field (IMF) conditions, taking advantage of the crossing events of these discontinuities by the Cluster spacecraft. With an enhancement of southward IMF B_Z, the surface current at HLMP reduces, while increasing at the bow shock. Since the amount of the magnetospheric current increases with the increase of southward IMF B_Z, a synthesis analysis based on the Cluster observations suggests the bow shock and HLMP together contribute to the magnetospheric current system, and the bow shock would become an important current generator when the southward IMF B_Z becoming large. This scenario accords with the previous global magnetohydrodynamic (MHD) simulations.