Global MHD simulation of Kronian magnetosphere with solar wind data from Cassini

In a series of simulation studies we have reported that vortices form at Saturn's dawn magnetopause when the IMF was northward. We interpreted these vortices as resulting from the Kelvin Helmholtz (K-H) instability. Recent developments in computer performance and numerical calculation techniques have allowed us to perform global MHD simulations of the magnetosphere with much higher resolution (grid spacing 0.1RS) than was previously possible (0.3RS). These high-resolution simulations have sufficient resolution to model the signature of the field-aligned currents from the K-H vortices in Saturn's auroral ionosphere. We present new simulation results of small patchy regions of upward field-aligned current which may be related to auroral emissions. Recently, patchy aurorae resembling our results have been reported from Cassini observations. As a follow on study we have used Cassini observations of the solar wind upstream of Saturn to drive a global simulation of the Kronian magnetosphere from 2008-02-12/14:00:31 to 2008-02-13/01:59:31. In this period, the Cassini spacecraft was in the solar wind almost directly upstream of the magnetosphere. When an interplanetary shock reached Saturn large vortices formed in the magnetosphere which subsequently propagated tailward. In general the magnetopause position varied dynamically in response to changes in magnetospheric convection. In the polar region, we found a "streaky" configuration of field-aligned currents. It is thought that this field-aligned current configuration results from dayside magnetospheric convection. In this paper we will show simulation results from the entire interval and detailed analysis.