ULF Wave Modulation of Energetic Electron Precipitation Caused by the Self‐Limiting of Space Radiation: May 2024 Superstorm Observations

Abstract The May 2024 geomagnetic superstorm provided the opportunity to explore how strong wave‐particle interactions affect energetic electron precipitation under intense driving. Using coordinated measurements from a balloon‐borne Timepix‐based X‐ray detector, ground‐based riometers and magnetometers, and Arase satellite observations, we identified quasi‐periodic bursts of energetic electron precipitation coincident with Pc5 ultra low frequency (ULF) wave oscillations. Arase satellite data revealed energy‐dispersed trapped energetic electron flux modulations in the “seed” energy range, indicating that trapped electron flux was likely modulated by ULF waves. This letter reveals that these flux enhancements surpassed the Kennel‐Petschek (K‐P) limit, creating intense chorus waves and driving periodic electron precipitation. Drift‐dispersion analysis traced these modulations back to a source in the post‐noon magnetospheric sector, matching balloon and ground‐based measurements. Here, we propose a novel indirect ULF wave‐driven mechanism for modulated energetic electron precipitation, whereby periodic modulations of “seed” electron fluxes enhance electron losses.