AXISYMMETRICAL MODELING OF COMETARY MASS LOADING ON AN ADAPTIVELY REFINED GRID - MHD RESULTS

The first results of an axisymmetric MHD model of the interaction of a n expanding cometary atmosphere with the solar wind are presented. The model assumes that far upstream the plasma flow lines are parallel to the magnetic field vector. The effects of mass loading and ion-neutra l friction are taken into account by the governing equations, which ar e solved on an adaptively refined unstructured grid using a MUSCL-type numerical technique. The combination of the adaptive refinement with the MUSCL-scheme allows the entire cometary atmosphere to be modeled, while stiff resolving both the shock and the near nucleus of the comet . The main findings are the following: (1) A shock is formed approxima te to 0.45 Mkm upstream of the comet (its location is controlled by th e sonic and Alfvenic Mach numbers of the ambient solar wind flow and b y the cometary mass addition rate). (2) A contact surface is formed ap proximate to 5,600 km upstream of the nucleus separating an outward ex panding cometary ionosphere from the nearly stagnating solar wind flow . The location of the contact surface is controlled by the upstream fl ow conditions, the mass loading rate and the ion-neutral drag. The con tact surface is also the boundary of the diamagnetic cavity. (3) A clo sed inner shock terminates the supersonic expansion of the cometary io nosphere. This inner shock is closer to the nucleus on dayside than on the nightside.