Solar wind - Magnetosphere - Ionosphere Coupling in the GUMICS-4 Global MHD Simulation

This presentation discusses the magnetosphere - ionosphere coupling dynamics during substorm evolution in a global MHD simulation GUMICS-4. The ionospheric and magnetospheric evolution is followed during observed substorm events that have been run using the actual solar wind and IMF as model initial and boundary conditions. In addition to the standard 5-min resolution output from the simulation, specific periods were rerun in a mode that saves the output every 20 seconds. This allows us to analyze changes in the magnetosphere and ionosphere at intervals corresponding roughly to the Alfven travel time between the ionosphere and high-altitude magnetosphere. We examine the effects of the solar wind dynamic pressure and the orientation of the interplanetary magnetic field on the energy input into the magnetosphere through the magnetopause surface and its dissipation in the ionosphere. In the ionosphere, maps of the Pedersen and Hall conductances, auroral precipitation power, Joule heating, polar cap potential, and field-aligned currents are used in the analysis. In the magnetosphere, the location and shape of the tail current sheet is characterized using physical parameters such as magnetic field, current density, plasma velocity, mass flux, and energy flux in a coordinate system defined by the sheet. The results are used to discuss, in the framework of the MHD simulation, the solar wind driving of magnetospheric activity and the role of near-tail reconnection in the energy dissipation in the ionosphere.