The Dynamics of Saturn's Ultraviolet Aurorae

Bader, Alexander and Badman, Sarah and Ray, Licia (2020) The Dynamics of Saturn's Ultraviolet Aurorae. PhD thesis, Lancaster University.

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Abstract

Saturn’s aurorae are highly dynamic, controlled from within Saturn’s magnetosphere and by its interaction with the solar wind. This thesis investigates ultraviolet observations of these auroral emissions and corresponding in situ measurements of fields and particles, both mostly obtained by the Cassini mission, in order to separate different components of the aurorae and determine their origin. The brightest emissions are found to be generated by recurring magnetotail reconnection, the occurrence of which is controlled by solar wind conditions and the phasing of Saturn’s planetary period oscillation systems of rotating magnetic field perturbations and electric currents. The auroral signature resembles a series of bright patches emerging near local midnight and subcorotating with the planet’s rotation. Underlying these is a steady auroral band which may be driven by flow shears in the outer magnetosphere and is modulated in intensity and location by the rotating planetary period oscillation systems, accompanied by a dim equatorward outer emission which is suggested to be related to wave scattering of electrons in the inner ring current. Observations further show various small-scale transients such as short-lived ∼ 1 h quasiperiodic flashes possibly indicative of magnetodisc reconnection occurring predominantly near dusk, or numerous fine arcs only visible in the highest resolution imagery obtained by Cassini which may be related to interchange injection events. The relation between the source of auroral particles in the magnetosphere and the auroral emissions they generate upon impacting the atmosphere was investigated, with in situ measurements close above the aurorae revealing the presence of energetic field-aligned ion beams and conics as well as complex wave-particle interactions which may be responsible for their energization. While this thesis uncovers much unknown detail on the workings of Saturn’s aurorae, many questions remain to be answered in future research.