Effect of storm-time plasma pressure on the magnetic field in the inner magnetosphere

We investigate the effect of plasma pressure on the magnetic field in the near-Earth magnetosphere (2 to 6.5 R-E) during the major magnetic storm of October 21 - 25, 2001. For this we obtain a time series of snapshots'', in each of which the magnetic forces are equilibrated by plasma pressure gradient forces. Each snapshot is computed using our 3-D equilibrium code, which is fed anisotropic pressure in the equatorial plane from a kinetic ring current model. As computational boundaries we use magnetic flux surfaces obtained from the T89 empirical model [Tsyganenko, 1989], parameterized by the appropriate K-p. We analyze the computed magnetic fields and electric currents at each stage of the storm. Our findings include significant (similar to10) plasma beta and large field depressions near Earth at the storm peak. The results clearly show the necessity of a magnetically self-consistent treatment of plasma transport in storm modeling.