Relativistic electron pitch‐angle scattering by electromagnetic ion cyclotron waves during geomagnetic storms

During magnetic storms, relativistic electrons execute nearly circular orbits about the Earth and traverse a spatially confined zone within the duskside plasmapause where electromagnetic ion cyclotron (EMIC) waves are preferentially excited. We examine the mechanism of electron pitch‐angle diffusion by gyroresonant interaction with EMIC waves as a cause of relativistic electron precipitation loss from the outer radiation belt. Detailed calculations are carried out of electron cyclotron resonant pitch‐angle diffusion coefficients D αα for EMIC waves in a multi‐ion (H + , He + , O + ) plasma. A simple functional form for D αα is used, based on quasi‐linear theory that is valid for parallel‐propagating,…