Isolated Proton Auroras and Pc1/EMIC Waves at Subauroral Latitudes

Isolated proton aurora (IPA) in the subauroral ionosphere is created by energetic proton precipitation through wave-particle interactions with electromagnetic ion cyclotron (EMIC) waves in the conjugate inner magnetosphere. In this study, spatial distribution and occurrence probability of IPAs were statistically investigated as a proxy for regions of EMIC wave occurrence using ground-based imaging data during 2006-2012 at Athabasca, Canada. The 7-year average of the IPA occurrence probability over the total observation interval was estimated to be 0.83%, and a factor of 5 change was found between maximum and minimum years. Local time (between 16 and 06 MLT) distribution shows double peaks at premidnight and at dusk. The occurrence probability increases with Kp, and the MLT location tends to shift duskward. The statistical distribution of IPA size shows a clear peak at a spatial size of 10,000 km2, and latitudinal and longitudinal lengths have peaks at 56 and 340 km, respectively, at the ionospheric altitude. The equatorial projections of IPA source locations and two-dimensional (2D) structures are estimated by magnetic field tracing. These spatial structures are essential to quantitatively estimate the loss rate of energetic particles, contributing to space weather studies.