Rapid scattering of radiation belt electrons by storm-time EMIC waves

A storm main phase can produce a rapid depletion of electron fluxes in the Earth's outer radiation belt and the pitch-angle scattering by the electromagnetic ion cyclotron (EMIC) waves is one mechanism that might account for the electron losses. To efficiently scatter the bulk of the electron population, below 1-2 MeV, the EMIC waves would need to have significant power very near a heavy ion gyrofrequency. We present a wave event at the storm main phase and carefully examine the wave spectrum to identify the energy range of electrons scattered by the waves. The EMIC waves exhibit power right below the He+ gyrofrequency and we estimate that they can interact with electrons having energies as low as 400 keV producing rapid scattering at almost all pitch-angle values on the time scales of seconds. Our statistical analysis suggests that this event is not an exception; the majority of EMIC waves can scatter electrons with energies under 2 MeV. Our results show that EMIC waves can be one of the dominant radiation belt loss mechanisms during the storm main phase. Citation: Ukhorskiy, A. Y., Y. Y. Shprits, B. J. Anderson, K. Takahashi, and R. M. Thorne (2010), Rapid scattering of radiation belt electrons by storm-time EMIC waves, Geophys. Res. Lett., 37, L09101, doi: 10.1029/2010GL042906.