THE CLOSURE OF REGION-1 FIELD-ALIGNED CURRENT IN MHD SIMULATION

摘要

We have studied the closure path of Region-1 field-aligned current system in our global MHD simulation and found some interesting results. After leaving the ionosphere on the eveningside the current deviates from the field-aligned direction rather early and bends towards the Sun. After passing through the velocity shear region near the magnetopause, which is a generator region, it climbs up along the magnetopause, being more or less field-aligned. Because of this it again bends sunward. When approaching the noon-midnight meridian plane (Y = 0 plane in GSM coordinates), however, the current becomes more perpendicular to the magnetic field. It passes through the Y = 0 plane at about X = 2 +/- 1, Z = 11 +/- 1. On the morningside the closure path is a mirror reflection of that on the evening side. Thus the closure path seems to reside more on the dayside than perhaps usually thought. We give a simple physical explanation for the dayside bending, which is based on the MHD pressure balance equation. [References: 8]