Atmospheric Ionization Caused by EMIC-Wave Driven Energetic Electron Precipitation at Auroral Latitude

Electromagnetic ion cyclotron (EMIC) waves are recognized as one of the primary drivers of energetic electron precipitation (EEP) into the Earth's atmosphere. A problematic discrepancy has remained between the occurrence frequency of waves in magnetic local time (MLT) and the resultant precipitation observed by satellites. This study attempts to characterize the ionization profiles induced by EMIC-wave-driven EEP from ground-based measurements. Our combined observational data sets, comprising imaging riometer, atmospheric radar, and magnetometer data obtained at Syowa Station from 2016 to 2019, enable us to find more than 850 events of EMIC-driven EEP identified through concurrent ionization and EMIC wave activity. The MLT distribution of events peaks in the afternoon sector (13:00–14:00 MLT), consistent with the MLT distributions of waves previously reported. More than 60% of the events exhibit ionization above 60 km altitude caused by sub-MeV EEP, which is attributed to non-resonant scattering by EMIC waves.