Plasma Pressure Profile in Ring Current Region

The equilibrium equation in the field line coordinate system is derived in the ring current region where the Tsyganenko and Usmanov (TU) model of magnetic field is adopted. A generalized Euler difference method for solving two-dimensional equilibrium equations is developed. The numerical result show that a nearly isotropic plasma pressure profile exists in the ring current region. On the equator, with increasing L, the plasma pressure attend to more isotropic. Most of the results are in good agreement with observations.