Influences of IMF B_y Polarity on Dayside Electron Precipitation in Terms of Energy Channels

The B_y component of the interplanetary magnetic field (IMF) has long been suggested to play a crucial role in modulating precipitating electrons that create the dayside aurora. However, the effects of the B_y polarity on dayside precipitating electrons have never been examined in terms of energy channels. The present study statistically analyzes these effects using number fluxes of four energy channels. Our results show that the flux response of the dayside electron precipitation to the B_y polarity is not fixed in different energy channels. We infer that the response in the energy range of 688–1,000 eV is associated with interhemispheric field-aligned currents, while the response in the energy range of 154–224 eV is likely related to the direct entry of magnetosheath electrons via antiparallel reconnection. In addition, local time distributions of precipitating electrons reveal two types of preexisting hemispheric asymmetry regardless of the B_y polarities. The first (second) type, which appears in the 06–12 magnetic local time (MLT) (12–18 MLT) sector, indicates higher (lower) flux in the Southern Hemisphere than in the Northern Hemisphere. All of the present results improve our understanding at the dayside aurora and the IMF B_y effects on it, which would not have been retrieved without the use of individual energy channels.