Problems with Modeling Plasmasphere Refilling After Geomagnetic Storms

Abstract:

During geomagnetic storms, the plasma in the outer plasmasphere is depleted as the plasma drifts away from the Earth across magnetic field (B) lines due to storm-time electric fields. After the storm, the plasmasphere refills due to an upward flow of plasma from the ionosphere that is initially supersonic (H⁺). The current numerical models of plasmasphere refilling are typically based on a numerical solution of the ion (H⁺, O⁺, He⁺) and electron continuity, momentum, and energy equations. The equations are solved along closed magnetic field lines that connect conjugate ionospheres, with allowance for cross-B plasma drift during storms. Both diffusion and hydrodynamic approximations have been adopted. The diffusion approximation neglects the nonlinear initial term in the momentum equations, so this approximation is not rigorously valid for early refilling times (~ day). At high altitudes, the plasma becomes collisionless and there are different temperatures parallel and perpendicular to B (not included in current models). Also, single-stream and multi-stream (separate ion streams from the conjugate ionospheres) formulations have been adopted, and the refilling features are different. These and other problems with the current plasmasphere refilling models will be discussed.