GROWTH, SUDDEN ENHANCEMENT, AND RELAXATION OF CURRENT SHEETS IN THE MAGNETOTAIL - 2-DIMENSIONAL SUBSTORM DYNAMICS

A two-dimensional, low-dissipation magnetohydrodynamic simulation is used as a model for magnetospheric substorm dynamics. The simulation begins from a Grad-Shafranov equilibrium of the magnetotail including the Earth's dipole field. This initial configuration is driven by a continuous electric field (of IMF origin) which induces equatorward flows. A thin current sheet develops algebraically in time, spanning Y-points that stretch from the mid-tail region (similar to 30 R(E)) to the near-Earth region (similar to 10 R(E)). In the late growth phase, rapid thinning of the sheet and near-explosive intensification of the current density are observed. The onset of a partial current disruption results from the formation of small islands in the near-Earth region. Numerical results are compared with observations.