A Hydrodynamic Model for Plasmasphere Refilling Following Geomagnetic Storms

The refilling of the plasmasphere following a geomagnetic storm remains one of the longstanding problems involving ionosphere-magnetosphere coupling. Both diffusion and hydrodynamic approximations have been adopted for the modeling and solution of this problem. The diffusion approximation neglects the nonlinear inertial term in the momentum equation and so this approximation is not rigorously valid immediately after a storm. The principle focus of this work is the formulation and development of a hydrodynamic refilling model (that includes the nonlinear inertial term) using the fluxcorrected transport method, a numerical method that is extremely well suited to handling nonlinear problems with shocks and discontinuities. In a previous study, this model has been validated against exact analytical benchmark problems and in this study, the model is used to describe plasmasphere refilling. The plasma transport equations are solved along 1-dimensional closed magnetic field lines that connect conjugate ionospheres and the model currently includes three ions (H+, O+, He+) and two neutral (O, H) species. In this study, each ion species under consideration has been modeled as two separate streams emanating from the conjugate hemispheres and the model correctly predicts supersonic ion speeds and the presence of high levels of helium during the early hours of refilling. The ultimate objective of this research is the development of a 3-dimensional model for the plasmasphere refilling problem, and with additional development, the same methodology can be applied to the study of other complex space plasma coupling problems in closed flux tube geometries