Kelvin-Helmholtz instability at Saturn's magnetopause: Cassini ion data analysis

Abstract

On 13 December 2004 Cassini, on approach to Saturn from the dawn flank, crossed the magnetopause multiple times. During these events the plasma spectrometer had a good field of view of both the magnetospheric and magnetosheath plasmas that often flow in nearly opposite directions (compared with more typical orientations that only allow one regime to be sampled). This fortunate viewing permitted ion plasma parameters to be measured, particularly flow speeds in both regions near simultaneously for the first time, facilitating detailed investigation of the multiple boundaries crossings. This allowed different plasma regions to be identified via analysis of thermal ion data (plasma velocity, densities and temperatures of protons and water group ions) and a search for Kelvin-Helmholtz instabilities to be undertaken. This interval had previously been studied by Masters et al. (2010), who identified a single Kelvin-Helmholtz vortex, however their study lacked ion plasma parameters and a measured flow speed. The new processed ion data set presented here supports their identification and identifies a second vortex ∼3 h earlier, highlighting the value of ion plasma parameters to such studies.