Simulation of EMIC wave excitation in a model magnetosphere including structured high‐density plumes

Abstract

The HOTRAY code is used to evaluate the path integrated gain of electromagnetic ion cyclotron (EMIC) waves as a function of frequency in two propagation bands above the O+ and He+ gyrofrequencies. Calculations are performed over a range of L shell (3 < L < 7) assuming a cold H+‐He+‐O+ plasma with an additional bi‐Maxwellian hot ring current proton distribution. The cold plasma model includes a plasmasphere and high‐density storm time plume region containing spatial density fluctuations. The strongest wave gain (>40 dB) is found near the plasmapause, within regions with density structure in the plume, and in the low‐density trough at L ≥ 6.5. As a self‐consistent test on whether EMIC waves play an important role in relativistic electron loss from the radiation belts, the minimum cyclotron resonant electron energy is evaluated as a function of wave frequency and L shell for those EMIC waves that exhibit significant gain. The lowest electron resonant energies (approximately a few MeV) are found in structured plumes. The sensitivities of both the wave gain and electron minimum resonant energy to variation in thermal ion compositions, the energetic proton properties, or plume density structure are also investigated.