Wednesday

This talk will present observations of polar cap arc sub-structure down to unprecedented spatial and temporal scales. Two events containing polar cap arcs occurring over Svalbard are investigated: the first occurred on 4th February 2016 and is consistent with formation on closed field lines; the second occurred on the 15th December 2015 and is consistent with open field lines. These events were identified using global scale images from the Special Sensor Ultra-violet Spectrographic Imager (SSUSI) instruments on board Defence Meteorological Spacecraft Programme (DMSP) spacecraft. Intervals when the arcs passed through the small field of view of the Auroral Structure and Kinetics (ASK) instrument, located on Svalbard, were found using images from a co-located all sky camera. The structure from the two events are compared to each other and to previous ASK observations when it was located in Tromsø, under the auroral oval. The energy and flux of the precipitating particles above these arcs are estimated using the ASK observations in conjunction with the Southampton Ionospheric model. These estimates are compared to in-situ DMSP particle measurements to infer further information about their formation mechanisms. The structure of the polar cap arcs and the energy estimated for each event are found to be consistent with formation on different magnetic field topologies.