Solar wind-magnetosphere coupling at Saturn
thesisposted on 10.07.2007, 08:46 by Caitriona M. Jackman
The studies contained within this thesis concern solar wind-magnetosphere coupling at Saturn. The first study uses data from the Cassini mission when it was upstream of Saturn to investigate the large-scale structure of the heliosphere and the interplanetary magnetic field (IMF) at 9 AU. The medium is found to be consistent with that expected during the declining phase of the solar cycle, structured by corotating interaction region (CIR) compressions and rarefactions. An empirical formula for open flux production at Saturn’s magnetopause is presented. Estimates of open flux production associated with a period of strong solar activity indicate that major magnetospheric dynamics were excited by reconnection-mediated solar wind interaction during the interval. The second study begins by examining concurrent IMF and Saturn kilometric radiation (SKR) data together with images from the Hubble Space Telescope from an interval in January of 2004, which show the effect of the arrival at Saturn of a CIR-related compression region. On examination of the IMF data surrounding the Saturn orbit insertion interval, it is suggested that a compression of similar character impinged on the magnetosphere at some point during the fly-through. Observations on the outbound pass show strong bursts of SKR extending to low frequencies, and provide evidence for the first specific link between SKR emission features and in situ dynamics inside Saturn’s magnetosphere. The third study comprises a theoretical model of the flows and currents in Saturn’s polar ionosphere under conditions of strong Dungey-cycle driving. The flow pattern consists of components which are intended to represent plasma sub-corotation in the middle magnetosphere region, and the Vasyliunas- and Dungey-cycles of convection at higher latitudes. The model results indicate a strong dawn-dusk asymmetry in Saturn’s main auroral oval under active Dungey-cycle conditions, and are in good agreement with observations.