Kelvin-Helmholtz Instability at the Dawn Flank of Saturn's Magnetopause

Crossings of Saturn's magnetopause made by the Cassini spacecraft between 12 and 17 March 2006 are analysed. Magnetic field and plasma data are used to identify excursions into the magnetosheath bounded by crossings of the magnetopause current layer. During most of this period Cassini's trajectory was approximately parallel to the magnetopause boundary given by a model of the surface. Minimum variance analysis (MVA) of the magnetic field vector measurements is used to determine the normal to the boundary for each crossing of the current layer. The normals corresponding to the crossings made on 12, 13 and 17 March oscillate about the normal predicted by the surface model. This suggests the presence of regular boundary waves with a direction of propagation found to be close to parallel to Saturn's rotational equator, and not coincident with the expected solar wind flow direction in the local magnetosheath. Based on this propagation direction and the magnetospheric and magnetosheath magnetic fields we propose that these waves were generated by the Kelvin-Helmholtz instability. In addition we discuss the possibility that on 15 and 16 March nonlinear Kelvin-Helmholtz waves produced a strongly perturbed magnetopause boundary that may have led to local magnetic reconnection.