Properties of quasi-periodical emission of electromagnetic ion cyclotron waves

Energetic electron scattering by electromagnetic ion cyclotron (EMIC) waves is one of the most effective mechanisms of electrons losses in the inner magnetosphere. Such resonant scattering has been traditionally considered as a controlling process for the dynamics of relativistic electron fluxes in the Earth’s radiation belts. EMIC wave generation is mainly associated with the ring current ion population injected from the plasma sheet. These ions 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 by strong ultra-low-frequency (ULF) waves that modulate a quasi-periodical ion anisotropy responsible for EMIC excitation. Using THEMIS spacecraft observations of simultaneous EMIC waves and compressional ULF waves, we investigate the statistical properties of such quasi-periodic EMIC emission. 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.