A Magnetohydrodynamic Simulation Study of the Dynamic Variations in the Configuration, Convection and Auroral Emissions in Saturn’s Magnetosphere Driven by the Observed Solar Wind

Abstract:

In our previous simulations we have used constant and simple solar wind conditions to understand the basic behavior of the Kronian magnetosphere. In this study we used Cassini observations of the solar wind upstream of Saturn to drive a massively parallel simulation. Using these solar wind data we simulated the Kronian magnetosphere from 2008-02-12/14:00:31 to 2008-02-13/01:59:31. During this interval the Hubble Space Telescope (HST) observed Kronian UV auroral emissions. For these solar wind conditions there are several enhancements of the solar wind dynamic pressure (shocks) and a polarity reversal in the IMF components.

From these simulations we obtained the dynamically changing shape and convection pattern of the Kronian magnetosphere in response to the variations in solar wind dynamic pressure and IMF direction. For instance the magnetopause and bow shock location at the subsolar point changed by 40% during one solar wind pressure increase and 22% during another. After the pressure increases a layered convection pattern formed between the corotation dominated region and the magnetopause. The layers in this convection system interacted with each other, forming large vortices. We calculated the configuration of field aligned currents from the simulation and found layered and patchy distributions in the ionosphere. The pattern of these upward field aligned currents (FACs) in the dawn side ionosphere resembles the configuration of auroral emissions observed by HST well. To confirm the relationship between the layered configuration and upward FACs, we have calculated the footprint of magnetic field lines from the layered convection pattern to the polar region.