Measured Correlations of Auroral Emissions from Jupiter and Saturn With Solar Wind Variations

An extended set of Hubble Space Telescope (HST) observations of the UV auroral emissions from Jupiter and Saturn has been carried out in three campaigns over Jan.-June 2007. This is by far the most extensive series of remote high resolution imaging of planetary aurora to date, and provides new physical insight into the cause and effect relationships governing the controlling processes for the giant planet auroral emissions. Simultaneous in situ measurements of local solar wind and magnetospheric plasma conditions have been made during two of these campaigns by Cassini at Saturn in Jan. 2007 and by the New Horizons mission approaching Jupiter in Feb. 2007. The UV auroral emission brightness and distributions have also been compared with estimates of the solar wind conditions near each planet extrapolated from near-Earth measurements, which can be verified by comparison with Cassini and New Horizons in situ data. It has been found that there is a good correlation at both planets between total auroral power and solar wind dynamic pressure, at least for the major solar wind disturbances arriving at each planet. At the same time, the nature of the auroral brightenings differs between Jupiter and Saturn, and the source regions of auroral activity are quite different in the two magnetospheres. In this presentation, the HST and solar wind data and the nature of the correlations will be presented. The physical significance of the correlations will be discussed, based on the much denser set of measurements now available.