THE EFFECT OF THE MAGNETOPAUSE SHAPES OF JUPITER AND SATURN ON MAGNETOSHEATH PARAMETERS

The solar wind flow past nonaxisymmetric magnetospheres exhibits featu res which are absent in the case of axisymmetric magnetospheres such a s that of Earth. We discuss results obtained by a numerical integratio n of the dissipationless MHD equations, under simplifying assumptions, and apply them to the two outer planets Jupiter and Saturn, both of w hose magnetospheres depart substantially from axisymmetry. We model th ese magnetospheres as paraboloids with two different radii of curvatur e at the subsolar point, L-0 and L-1, where L-0 and L-1 refer to a mag netopause cut containing the rotational axis, and to the rotational eq uator, respectively (L-0 < L-1). The degree of flattening is expressed by a parameter q := L-0/L-1, and, following earlier modelling and dat a 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 i n 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 stro ng 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 inter mediate orientation, a smooth rotation of the m agnetosheath magnetic field towards the direction of the planet's rota tional axis is superimposed on the field strength enhancement (and the density reduction) as the respective magnetopauses are approached. Fo r Saturn, we study the dependence of magnetosheath parameters for vari ous IMF orientations at two Alfven Mach numbers. Throughout, we compar e our results to similar calculations of solar wind flow past Earth. ( C) 1998 Elsevier Science Ltd. All rights reserved.