Magnetospheric Current Sheets and Boundary Layers

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The proposed work represents continuation of an ongoing research program concerned with some of the physical processes and structures that occur in thin electrical current sheets and plasma boundary layers in the Earth's magnetosphere, with special emphasis on the magnetopause. This current sheet forms the outer boundary of the magnetosphere and separates it from the rapidly streaming solar wind. The proposed research is concerned with five related problem areas: o Construction, from spacecraft data, of magnetic field "transects" describing the draping of magnetic field inside or outside the magnetopause over elongated bulges moving in a transverse sense along that layer. The result will be a robust and thoroughly bench-marked data analysis tool that can be used by other researchers. Applications include, not just traveling bulges and waves on the magnetopause, but other moving current filaments, e.g., in the low latitude boundary layer or in the geomagnetic tail. o Construction of similar transects describing mesoscale magnetic structures, such as tearing mode islands, in the magnetopause itself. Again, the goal is to develop and test a robust data analysis tool that is expected to be of utility and importance for study of two-dimensional structures in the magnetopause. o Theoretical study of weakly nonlinear wave pulses propagating on the magnetopause and their relation to observed bulges moving along that year. o Theoretical study of strong nonlinearities in steady, two- dimensional, field-aligned MHD flows, including transitions between elliptic and hyperbolic states. Search for, and analysis of, illustrative events in spacecraft data. o Theoretical study of MHD flow in two-dimensional reconnection layers. In each area, the research will start with analytical and associated numerical work, including, where appropriate, the generation of synthetic spacecraft data for bench marking of the data analysis techniques; this phase will be followed by identificaion of sample events and by testing of the new techniques on spacecraft data, initially from AMPTE/IRM, but later in the project, from the CLUSTER mission.