Abstract
A model is presented in which the plasma sheet is not confined by a closed magneticfield configuration. Instead, the plasma-sheet particles continually leak down the tail along open field lines; the loss rate is controlled by particle scattering with magnetic-field irregularities and waves, and the length of the plasma sheet is determined by loss of plasma-sheet particles to the neutral sheet. The escaping particles are replaced by continuous injection of magnetosheath plasma entering the magnetosphere through the demarcation lines on the dayside magnetopause. According to the model, plasma-sheet particle fluxes at the lunar distance in the tail should normally be less than fluxes observed at the Vela orbital distance by a factor of two or more. The substorm onset in this model is the result of a depletion of the near-Earth plasma sheet owing to enhanced downstream escape. Thus the plasma-sheet ‘drop-out’ observed at the Vela distance should be accompanied by a temporary enhancement of plasma-sheet flux at the lunar distance. Rapid magnetic merging then proceeds in the near-Earth neutral sheet by a simple ‘vacuum merging’ process until the merging is slowed by the reappearance of the plasma sheet near the peak of the substorm.
Published Version
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