Static magnetic field models consistent with nearly isotropic plasma pressure, Geophys

Abstract. Using the empirical magnetospheric magne-tic field models of Tsyganenko and Usmanov (TU), we have determined the self-consistent plasma pressure gra-dients and anisotropies along the midnight meridian in the near-Earth magnetosphere. By "inverting " the mag-netic field, we determine what distributions of an an-isotropic plasma, confined within the specified magnetic field configuration, are consistent with the magnetohy-drostatic equilibrium condition, J x B = X7. P. The TU model, parameterized for different levels of geomag-netic activity by the Kp index, provided the magnetic field values from which J x B was numerically evalu-ated. A best fit solution was found that minimized the average difference between J x B and X7 ß P along an entire flux tube. Unlike previous semi-empirical mod-els, the TU models contain magnetic stresses that can be balanced by a nearly isotropic plasma pressure with a reasonable radial gradient at the equator