An investigation into the fine-scale structure of polar cap aurora using ground-based and spacecraft instrumentation

Abstract

This thesis will investigate the formation and structure of polar cap arcs using groundbased and spacecraft instrumentation. In particular, we present polar cap arc substructure down to unprecedented spatial and temporal scales using the Auroral Structure and Kinetics (ASK) instrument. Events are identified using images from Special Sensor Ultra-violet Spectrographic Imager (SSUSI) instruments on board Defence Meteorological Satellite Program (DMSP) F16-F19. Three studies are presented. First, an event with polar cap arcs occurring on the dawn and duskside of the northern hemisphere on 19 January 2008 was observed by SSUSI instruments on board DMSP F16 and F17. The structure on the duskside occurred over Svalbard and was analysed using a multitude of ground-based instrumentation, including ASK, and was found to be consistent with formation on closed field lines. The arc on the dawnside of the northern hemisphere was found, using in-situ particle data, to be consistent with formation on open field lines. This first study shows that polar cap arcs consistent with different formation mechanisms can occur simultaneously. The second study surveyed SSUSI and corresponding SSJ/5 data to identify and classify polar cap arc events in December 2015. Further examples of arcs occurring on both magnetic field topologies are found as well as examples that are not, at first sight, consistent with either. The occurrence frequency of polar cap arcs is also investigated and they are found to be present in the SSUSI images at least 20% of the time. Finally, two events with polar cap arcs consistent with different magnetic field topologies occurring over Svalbard are analysed using ASK data. The first occurred on 4 February 2016 and is consistent with formation on closed field lines; the second occurred on 15 December 2015 and is consistent with open field lines. The small-scale structure within these arcs is found to be quite different and consistent with their occurrence on different magnetic field toplogies. The ground-based observations are then compared to the spacecraft observations to infer more information about the two formation mechanisms.

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Identifiers

ORCID for Robert Fear: orcid.org/0000-0003-0589-7147

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