3D resistive MHD computations of magnetospheric physics

Abstract

Numerical modeling of magnetospheres involves a number of aspects of magnetospheric physics, which may roughly be divided into global, local and microscopic dynamics. Global dynamics should include the interaction of the magnetosphere with the stellar wind plasma and of different parts of the magnetosphere with each other. By local dynamics we address the physics of a certain part of the magnetosphere with a reduced number of length and time scales. Examples are the plasma and energy transport at the magnetopause or in the magnetotail. Important transport coefficients for global and local processes are determined by the microscopic plasma dynamics. Clearly a selfconsistent modelling including all of these aspects is far beyond today's computer facilities. Even the rather different length and time scales in modeling one of the mentioned aspects of magnetospheric physics requires careful consideration.In this paper we will concentrate on the local dynamics of the magnetopause with special emphasis on the formation of flux transfer events (FTE'). FTE's seem to contribute a significant if not the dominant part of the plasma and energy transport from the solar wind into the earth's magnetosphere. We will summarize the conditions for modeling these phenomena due to different length scales, plasma parameters and relevant instabilities. The results of a three-dimensional resistive MHD code will be presented, which has been developed for this application. This code offers the option of using the Lax-Wendroff or the leapfrog integration scheme, where large efficiency has been achieved by a high degree of vectorization and the use of a nonuniform grid for three Cartesian directions.The results obtained by this MHD code recover typical observational features of FTE's, e.g. the bipolar signature of the magnetic field component normal to the magnetopause. Some conclusions concerning the observations of FTE's will be drawn. Furthermore we will compare these results with theoretical considerations.