The effect of the magnetopause shapes of Jupiter and Saturn on magnetosheath parameters

The solar wind flow past nonaxisymmetric magnetospheres exhibits features which are absent in the case of axisymmetric magnetospheres such as that of Earth. We discuss results obtained by a numerical integration of the dissipationless MHD equations, under simplifying assumptions, and apply them to the two outer planets Jupiter and Saturn, both of whose magnetospheres depart substantially from axisymmetry. We model these magnetospheres as paraboloids with two different radii of curvature at the subsolar point, L0 and L1, where L0 and L1 refer to a magnetopause cut comtaining the rotational axis, and to the rotational equator, respectively (L0 < L1). The degree of flattening is expressed by a parameter q:= L0L1, and, following earlier modelling and data analysis work, we set q = 0.35 for Jupiter and q = 0.64 for Saturn. We find here that the structure and behaviour of physical parameters in the magnetosheath of Saturn is intermediate to that at Earth and at Jupiter. For both planets, the thickness of the magnetosheath and the width and structure of the plasma depletion layer are found to be strong functions of the orientation of the interplanetary magnetic field (IMF). The effect of the IMF on the magnetosheath is strongest (weakest) when the IMF is directed perpendicular (parallel) to the rotational equator. For any intermediate orientation, a smooth rotation of the magnetosheath magnetic field towards the direction of the planetʹs rotational axis is superimposed on the field strength enhancement (and the density reduction) as the respective magnetopauses are approached. For Saturn, we study the dependence of magnetosheath parameters for various IMF orientations at two Alfvén Mach numbers. Throughout, we compare our results to similar calculations of solar wind flow past Earth.