Studies of Saturn's ultraviolet auroras using the Hubble space telescope

• Main Author: Meredith, Calum James
• Other Authors: Cowley, Stanley ; Stallard, Thomas
• Published: University of Leicester 2015
• Subjects: 522
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.697416

In this thesis we study Saturn’s ultraviolet dayside auroras mainly using images from the Hubble Space Telescope. We investigate a variety of different types of auroral emission observed in the database of images compiled between 1997 and 2013. In equinoctial data from 2009 two different types of features are investigated. In the dawn sector patches of emission are observed that are found to lack direct conjugacy between the two hemispheres and instead are displaced in local time. A production mechanism related to ULF waves is suggested, plausibly driven by drift-bounce resonance. Dusk transient auroral emission is also observed and found to be strictly non-conjugate. A suggested explanation is that the transient patches are related to newly-opened flux tubes where the hemispheric symmetry is broken via the interplanetary magnetic field Y component. A further study uses data from the Cassini spacecraft during passages through the solar wind in conjunction with Hubble Space Telescope images from 2011 and 2012 in order to investigate how changes in the Interplanetary Magnetic Field strength affect the auroral emission at Saturn. It is found that during intervals of positive interplanetary magnetic field the auroral emission in the dusk sector is enhanced as opposed to cases of negative field strength where there is little emission observed in the dusk sector. This supports earlier interpretations that this emission is due to low latitude dayside reconnection and open flux production. The final study in this thesis uses the entire dataset of Hubble Space Telescope images to investigate auroral storm events. There are 12 such events found in the database with statistics showing that storms are present ~12% of the time. We deduce from the statistics and observations that storms are likely to last ~16 hours or ~1.5 Saturn rotations.