Global MHD simulations of the interaction between Saturn's magnetosphere and the solar wind (Invited)

At Saturn, both the external (the solar wind) and the internal (the planet’s rotation and internal plasma source) conditions play an important role in affecting the global structure and dynamics of the magnetosphere. We have used 3D global MHD simulations to investigate the global configuration and dynamics of Saturn’s mass-loaded magnetosphere under different solar wind conditions. Our present model (BATSRUS) adopts a high-resolution, non-uniform spherical grid, which is crucial for capturing fine structures of the large-scale magnetospheric currents responsible for the coupling between the magnetosphere and the ionosphere. In order to examine the effects of the solar wind driving on dynamics of Saturn’s magnetosphere, we have used an idealized solar wind input with features typical of those of Corotating Interaction Regions (CIRs) seen at Saturn’s orbit. Our simulation results indicate that periodic large-scale plasmoid formation occurs in Saturn’s magnetotail, independent of the IMF conditions. However, the periodicity of plasmoid formation in the tail appears to be strongly affected by the upstream solar wind conditions. In this talk, we will compare the global magnetospheric configuration under different solar wind dynamic pressure and IMF conditions. In particular, we will discuss the interplay between the so-called “Vasyliunas-cycle” and “Dungey-cycle” in controlling the global plasma convection in Saturn’s magnetosphere. We will also show the ionospheric response to the solar wind driving, such as changes in the field-aligned currents and convection pattern, and discuss their relationship with dynamics in the magnetosphere.