Cassini observations of the Interplanetary Medium Upstream of Saturn and their relation to the Hubble Space Telescope aurora data

Abstract

We present Cassini magnetometer and plasma data for the January 2004 ‘solar wind campaign’ in which the particles and fields instruments monitored the solar wind and interplanetary magnetic field, while the Hubble Space Telescope (HST) simultaneously observed the UV aurora in Saturn’s southern ionosphere. Clear structuring is evident in the data which is associated with the highly developed nature of corotating interaction regions (CIRs) at this distance. The interplanetary medium during January consisted of four distinct types of behaviour. We see a ‘major’ compression region at the start of the interval followed by a rarefaction region, a ‘minor’ compression region, an ‘intermediate’ rarefaction region, and another major compression region at the end of the month. The highly dynamic nature of Saturn’s aurora revealed by the HST observations appears to relate directly to the concurrent solar wind activity measured by Cassini. Collectively these data provide a unique insight into the solar wind driving of Saturn’s magnetosphere and consequent auroral response.