Impact of EMIC‐wave driven electron precipitation on the radiation belts and the atmosphere

In recent years there has been a growing body of direct experimental evidence demonstrating electromagnetic ion cyclotron (EMIC) waves driving energetic electron precipitation (EEP) at unexpectedly low, sub‐MeV energies — as low as only a few hundred keV. EMIC wave driven scattering at these energies has important ramifications for our understanding of not only radiation belt electron dynamics, but also the importance of EMIC‐driven EEP to the chemical balance of the Earth’s atmosphere. In this study, we use three experimentally derived EMIC‐driven EEP flux spectra to investigate the impact of this precipitation on trapped radiation belt fluxes. In doing so, we resolve an apparent contradiction with earlier results derived from trapped electron flux populations that suggested EMIC waves only caused significant scattering at ultra‐relativistic energies. We show that strong sub‐MeV EEP measurements are not necessarily mutually exclusive with a strongly relativistic‐only trapped flux response, as the sub‐MEV peak precipitation is comparatively much smaller than the trapped population at those energies. Using a further six EEP spectra, we also demonstrate that EMIC‐driven EEP can generate significant ionisation of the Earth’s atmosphere above 40km, leading to the loss of mesospheric ozone. We find poor correlation between EMIC‐driven EEP fluxes and geomagnetic activity proxies, such that EMIC‐driven EEP is likely to be poorly specified in the forcing factors of modern coupled‐climate models.

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