The dynamics of Saturn's main aurorae

Bader, Alexander and Badman, Sarah and Cowley, S. W. H. and Yao, Zhonghua and Ray, Licia C and Kinrade, Joe and Bunce, E. J. and Provan, G. and Bradley, T. J. and Tao, Chihiro and Hunt, G. J. and Pryor, W. (2019) The dynamics of Saturn's main aurorae. Geophysical Research Letters, 46 (17-18). pp. 10283-10294. ISSN 0094-8276

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Abstract

Saturn's main aurorae are thought to be generated by plasma flow shears associated with a gradient in angular plasma velocity in the outer magnetosphere. Dungey cycle convection across the polar cap, in combination with rotational flow, may maximize (minimize) this flow shear at dawn (dusk) under strong solar wind driving. Using imagery from Cassini's Ultraviolet Imaging Spectrograph, we surprisingly find no related asymmetry in auroral power but demonstrate that the previously observed “dawn arc” is a signature of quasiperiodic auroral plasma injections commencing near dawn, which seem to be transient signatures of magnetotail reconnection and not part of the static main aurorae. We conclude that direct Dungey cycle driving in Saturn's magnetosphere is small compared to internal driving under usual conditions. Saturn's large‐scale auroral dynamics hence seem predominantly controlled by internal plasma loading, with plasma release in the magnetotail being triggered both internally through planetary period oscillation effects and externally through solar wind compressions.