Modelling the Compressibility of Saturn's Magnetosphere

Work presented at this meeting by Pilkington et al. shows observational evidence that Saturn's magnetopause may be significantly affected by variations in the beta parameter of the outer magnetospheric plasma, as well as by variations in solar wind dynamic pressure. In order to model the influence of these two physical parameters on magnetospheric compressibility, we construct magnetostatic models of the dayside magnetosphere of the planet using the UCL Magnetodisc Model in 'Saturn mode'. For different values of hot plasma beta, which span the observed range at Saturn, we construct a model power law expressing the relation between between magnetopause standoff distance and solar wind dynamic pressure (assumed to be equal to total magnetic plus plasma pressure at the model's outer boundary). We comment on the behaviour of the magnetospheric compressibility and scale according to: (1) The response of the magnetopause location to changes in solar wind dynamic pressure at fixed plasma beta; and (2) The response of the system which ensues when plasma beta varies at fixed solar wind dynamic pressure.