ON DIPOLARIZATION AND ITS RELATION TO THE SUBSTORM CURRENT WEDGE

Within the framework of our three-dimensional self-consistent MHD model of magnetotail activity we investigate near-Earth properties of magnetospheric substorms. Particular emphasis is on the generation mechanism and the three-dimensional aspects of the B(z) increase which is commonly called magnetic field dipolarization, and its spatial and temporal relation to the field-aligned currents of the substorm current wedge and the current reduction and diversion. We find that the dipolarization can be understood as the flux pileup due to the slowing down of the fast earthward flows carrying reconnected flux from the reconnection region. The gradients of B(z) at the dawn and dusk flanks of the dipolarization region contribute to the region 1 field-aligned current system of the substorm current wedge. The major contribution, however, is found to be associated with the shear between the y and x components of the magnetic field. We also find that the region where the cross-tail current is reduced ("disrupted") and diverted is located tailward from the dipolarization region. Our results indicate that the apparent tailward propagation of dipolarization effects does not support the conclusion that the underlying process is initiated further earthward.