| dc.description.abstract | We investigate how the location, size, and intensity of the auroral oval is affected by the combination of a strong dawn/dusk component of the interplanetary magnetic field (IMF By) during northward IMF and the tilt of the Earth’s magnetic dipole axis. Under sunlit conditions, aurora observations are contaminated by a strong dayglow signal. The extent to which this contamination influences the estimates of the average sunlit auroral intensities is currently unknown, motivating us to develop a new separation technique, where we fit a convoluted distribution to the data and extract the best fitting parameters. We applied the separation method to data obtained by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) onboard the Defense Meteorological Satellite Program’s (DMSP) F16-19 satellites. Dayglow modelling has significant uncer-tainties, which increase with increasing amounts of sunlight. We demonstrate to what extent this can influence quantitative estimates of the average auroral intensities. By applying our separation method to SSUSI observations made during stable and strong IMF By conditions over many years, the auroral component is isolated, and estimates of auroral intensities during sunlit conditions are improved. The separation method produced 30–40% higher auroral intensities than common statistical methods such as the mean. Statistics of the auroral component show a clear and substantial (∼500 km) dawn-dusk shift in the polar cap location depending on the sign of IMF By during local summer in the Northern Hemisphere for strong IMF By conditions. However, this shift is absent during local winter. We propose that the cause of this seasonally dependent shift in the polar cap location is likely to be related to seasonal differences in lobe reconnection rates. To our knowledge, this seasonal dependence has not been previously reported. In addition, by investigating the performance of our separation method, we suggest that previous methods have underestimated the statistical auroral intensities during sunlit conditions. | |
