Statistics of Quasi-periodic Bursts of Electromagnetic Ion Cyclotron Waves driven by Compressional Ultra-low-frequency Waves

Local and rapid losses of ultra-relativistic electrons in the inner magnetosphere are believed to be due to their resonant interactions with electromagnetic ion cyclotron (EMIC) waves. Such resonant scattering by EMIC waves has been traditionally considered as a controlling process for the dynamics of ultra-relativistic electron fluxes in the Earths radiation belts. EMIC wave generation is mainly associated with injections of plasma sheet energetic ions, which are drifting westward and generate the most intense EMIC waves on the dusk flank. In this work, we consider an alternative mechanism of EMIC wave generation due to local plasma compression that results in ion anisotropy responsible for EMIC excitation. Using THEMIS spacecraft observations of simultaneous EMIC waves and compressional ultra-low-frequency waves, we investigate the statistical properties of such quasi-periodic EMIC emissions. We show spatial distributions of ULF-modulated EMIC waves, statistics of their amplitudes and typical frequencies. We also discuss the associated measurements of ULF-modulated hot ion populations responsible for EMIC wave generation.