EMIC-driven electron trapped flux dropouts at sub-MeV, relativistic, and ultrarelativistic energies: results from POES and GPS

Electromagnetic ion cyclotron (EMIC) waves have long been known to be capable of scattering energetic electrons into the loss cone, and thus the Earth's atmosphere. For many years, this was believed to be a strictly relativistic phenomenon, largely restricted to energies of 1-2 MeV and above. In recent years, however, it has been observed experimentally that the interaction between EMIC and electrons can occur at energies as low as 100-200 keV [1,2]. Although several mechanisms to explain this phenomenon have been posited, no theory has as yet emerged as the likely dominant driver of this sub-MeV electron scattering. Despite significant evidence to support EMIC-driven sub-MeV electron scattering in the form of in-situ and ground-based observations of electron precipitation, there has been little evidence to support this from trapped flux studies. In part this is due to a difference in the intent of these studies, with trapped flux studies typically investigating the impact of electron scattering on the total radiation belt electron population, while precipitation studies are more interested in the impact on the Earth's ionosphere and atmosphere [3]. In this presentation, however, we show that using appropriate statistical averaging on a large enough dataset, it is possible to demonstrate significant depletions in global sub-MeV trapped electron fluxes in response to EMIC-driven scattering. Using trapped flux data from the Global Position System (GPS) satellite constellation, we show that EMIC-driven scattering causes significant reductions in trapped fluxes at energies as low as 120 keV. Furthermore, we show that although scattering does occur at sub-MeV energies, EMIC waves preferentially cause substantial depletions of ultra-relativistic electrons from the radiation belts. Using these results, we discuss why the apparent disagreement between trapped and precipitation studies of EMIC-driven electron scattering is actually expected, and does not present any contradiction. This work has been published in Hendry et al. [2021a] and Hendry et al. [2021b] [4,5].

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