Growth, sudden enhancement, and relaxation of current sheets in the magnetotail: Two‐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 (∼30 R_E) to the near‐Earth region (∼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.