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Abstract Electromagnetic ion cyclotron (EMIC) waves are known to be efficient for precipitating >1 MeV electrons from the magnetosphere into the upper atmosphere. Despite considerable evidence showing that EMIC‐driven electron precipitation can extend down to sub‐MeV energies, the precise physical mechanism driving sub‐MeV electron precipitation remains an active area of investigation. In this study, we present an electron precipitation event observed by ELFIN CubeSats on 11 January 2022, exclusively at sub‐MeV energy atL ∼ 8–10.5, where trapped MeV electrons were nearly absent. The THEMIS satellites observed conjugate H‐band and He‐band EMIC waves and hiss waves in plasmaspheric plumes near the magnetic equator. Quasi‐linear diffusion results demonstrate that the observed He‐band EMIC waves, with a high ratio of plasma to electron cyclotron frequency, can drive electron precipitation down to ∼400 keV. Our findings suggest that exclusive sub‐MeV precipitation (without concurrent MeV precipitation) can be associated with EMIC waves, especially in the plume region at highLshells.
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Parallel Acceleration of Suprathermal Electrons Caused by Whistler‐Mode Hiss Waves
Abstract Suprathermal electrons (~0.1–10 keV) in the inner magnetosphere are usually observed in a 90°‐peaked pitch angle distribution, formed due to the conservation of the first and second adiabatic invariants as they are transported from the plasma sheet. We report a peculiar field‐aligned suprathermal electron (FASE) distribution measured by Van Allen Probes, where parallel fluxes are 1 order of magnitude higher than perpendicular fluxes. Those FASEs are found to be closely correlated with large‐amplitude hiss waves and are observed around the Landau resonant energies. We demonstrate, using quasilinear diffusion simulations, that hiss waves can rapidly accelerate suprathermal electrons through Landau resonance and create the observed FASE population. The proposed mechanism potentially has broad implications for suprathermal electron dynamics as well as whistler mode waves in the Earth's magnetosphere and has been demonstrated in the Jovian magnetosphere.
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- PAR ID:
- 10375303
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 46
- Issue:
- 22
- ISSN:
- 0094-8276
- Page Range / eLocation ID:
- p. 12675-12684
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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