Abstract Electromagnetic ion cyclotron (EMIC) waves are recognized as a key driver of relativistic (>1 MeV) electron loss in Earth's magnetosphere. Growing evidence also suggests that EMIC wave can efficiently scatter sub‐MeV electrons, although the precise energy range and the underlying physical mechanisms remain debated. Here, we report a long‐lasting sub‐MeV electron precipitation event measured by the Relativistic Electron and Proton Telescope integrated little experiment‐2 (REPTile‐2) onboard the Colorado Inner Radiation Belt Experiment (CIRBE) CubeSat. We identify H + band EMIC waves as the main driver and find that the lower‐energy cutoff of the precipitating electrons is likely determined by the fractional EMIC frequency relative to the equatorial proton gyrofrequency. These findings underscore the role of H + band EMIC waves in scattering sub‐MeV electrons and provide new insights into the interaction processes between EMIC waves and radiation belt electrons.
Xiang et al. (Mon,) studied this question.