Geomagnetic Effects in Spatial Distributions of Particle Precipitation in Terms of Particle Energy Channels

This study examines the spatial distributions of precipitation during active and quiet times. Most previous studies commonly classified precipitation into different energy spectral types, but we utilized a classification according to particle energy channels. A general conclusion derived from these distributions suggests that regardless of active and quiet times, low-energy (<1 keV) and high-energy precipitating particles are mostly on the dayside and nightside, respectively. A comparison with past results reveals that the high-energy electron precipitation during quiet times is mostly due to wave scattering and that during active times is mainly produced by quasi-static potential structures (QSPS) and Alfvénic acceleration, while low-energy electron precipitation is mostly caused by QSPS and Alfvénic acceleration regardless of quiet and active times. For both high-energy proton and electron precipitation, the nightside dawn-dusk asymmetry of their distributions during active times is found to be opposite of that during quiet times. We infer that the distribution of high-energy precipitation during quiet times is dominated by the curvature and gradient drifts, while during active times it is mainly due to the physical processes or phenomena related to substorms in the magnetotail. Empirical orthogonal function analysis has been applied in this study to derive where the flux has the maximum enhancement as the geomagnetic activity increases. The results further demonstrate that low-energy and high-energy protons mainly increase in the noon and postmidnight sectors, respectively. The highest enhancements of low-energy and high-energy electrons are in the prenoon and premidnight sectors, respectively.