Journal of Geophysical Research: Space Physics

Computer simulation of inner magnetospheric dynamics for the magnetic storm of July 29, 1977

Authors

  • R. A. Wolf,

  • M. Harel,

  • R. W. Spiro,

  • G.-H. Voigt,

  • P. H. Reiff,

  • C.-K. Chen


Abstract

We present preliminary results of applying the Rice convection model to the early main phase of the magnetic storm of July 29, 1977. The computer model self-consistently computes electric fields and currents, as well as plasma distributions and velocities, in the inner-magnetosphere/ionosphere system. In the equatorial plane, the region modeled includes geocentric distances less than about the magnetopause standoff distance. Particle loss, parallel electric fields, and neutral winds are neglected. On the basis of solar wind parameters and the AL index as input, the model predicts the injection of plasma-sheet plasma to form a substantial storm time ring current. The total strength of the model-predicted ring current agrees accurately with the observed Dst index. Comparison of the model results with electric fields and Birkeland currents measured by S3-3 shows qualitative agreement but interesting quantitative discrepancies. During this event, region 1 currents, which in standard convection theory would connect to the outer magnetosphere, are observed as low as 60° invariant latitude at dawn and dusk. We examine the possibility that the magnetic field might be so highly inflated that 60° field lines extend to the outer magnetosphere. In the model, distortion of the inner edge of the plasma sheet by the magnetospheric compression associated with the sudden commencement temporarily disturbs the normal Birkeland-current pattern. The normal tendency for the plasma sheet's inner edge to shield low L values from the convection electric field is also temporarily disrupted. Normal Birkeland currents and shielding reassert themselves after about an hour. Time-integrated Joule heating in the model ionosphere over the first 5.5 hours of the storm main phase is about half the increase in model ring-current energy.

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