Incorporation of neutral cloud coupling in a global multifluid simulation of Saturn's magnetosphere

Saturn's magnetospheric dynamics are driven by two main phenomena: the action of the solar wind acting on its magnetopause, and the effects of corotation and mass-loading in the interior. Corotation is enforced due to field-aligned currents that transmit torque from the ionosphere to the plasma. The creation of new plasma in Saturn's inner magnetosphere and momentum loading processes both result in a breakdown of corotation. The spatial distribution of mass- and momentum-loading thus directly influences where corotation breakdown occurs and how the subsequent azimuthal plasma velocity profile develops, and therefore has a substantial effect on magnetospheric processes such as the Vasyliunas cycle. Saturn's main plasma source is a distributed cloud of neutral OH molecules sourced from Enceladus that occupies a significant portion of the inner magnetosphere. By including a distributed mass source in our global multifluid simulation, we investigate the global dynamics of Saturn's magnetosphere in response to realistic mass- and momentum-loading. The multifluid model enables the incorporation of multiple ion species, and thus allows us to account for the combination of protons and water group ions that populate Saturn's magnetosphere [Kidder et al., 2009]. We use the neutral cloud data of Jurac et al. [2002] to construct an empirical representation of the neutral cloud that we incorporate in our simulation as a source of ions due to photo- and impact ionization, as well as a source of momentum-loading from elastic and charge-exchange collisions. We also apply a realistic, latitudinally-varying ionospheric Pedersen conductivity based on data from Moore et al. [2010] in order to produce accurate magnetosphere-ionosphere coupling via field aligned currents.