On dipolarization and its relation to the substorm current wedge

The near-earth properties of magnetospheric substorms are investigated using the Hesse and Birn (1991) self-consistent 3D MHD model of magnetotail activity. The simulation shows that an increase of Bz, a decrease of the cross-tail current, and an increase of region-1 field-aligned currents occurs roughly simultaneously, consistent with the empirical picture described by McPherron et al. (1973). It was also found that the region where the cross-tail current is reduced and diverted is located tailward from the dipolarization region. The results indicate that the apparent tailward propagation of the dipolarization effects does not support an earlier suggestion that the underlying process is initiated further earthward.