Structure of the flank magnetopause for horizontal IMF: INTERBALL 1 observations

A case study is presented of a flank duskside magnetopause crossing by the INTERBALL 1 spacecraft during an interval of duskward horizontal interplane tary magnetic field. There is strong evidence that reconnection takes place in the flank magnetopause, where the draped sheath field has a large shear relative to the magnetospheric field. In our case the satellite was on the duskside above the equator. The assumed reconnection site is on the dusksi de of the northern flank slightly sunward at higher latitudes with respect to the satellite. The observations show energetic particles streaming along the field in the magnetosheath from the reconnection site, as expected. Th e deHoffman-Teller frame analysis shows that propagation of the magnetopaus e perturbations originates from the derived reconnection site. Observations are, in general, consistent with reconnection models that are based on the one-dimensional assumption. However, there is some significant deviation f rom the model prediction. We attribute the deviation to the presence of she ared plasma flow. The magnetopause in this case could not be described as a simple one-dimensional rotational discontinuity.