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Key factors determining nightside energetic electron losses driven by whistler-mode waves
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  • Ethan Tsai,
  • Anton V Artemyev,
  • Qianli Ma,
  • Didier Mourenas,
  • Oleksiy Agapitov,
  • Xiao-Jia Zhang,
  • Vassilis Angelopoulos
Ethan Tsai

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Anton V Artemyev
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Qianli Ma
University of California Los Angeles
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Didier Mourenas
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Oleksiy Agapitov
Space Science Laboratory, UC Berkeley
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Xiao-Jia Zhang
The University of Texas at Dallas
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Vassilis Angelopoulos
University of California Los Angeles
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Energetic electron losses by pitch-angle scattering and precipitation to the atmosphere from the radiation belts are controlled, to a great extent, by resonant wave particle interactions with whistler-mode waves. The efficacy of such precipitation is primarily controlled by wave intensity, although its relative importance, compared to other wave and plasma parameters, remains unclear. Precipitation spectra from the low-altitude, polar-orbiting ELFIN mission have previously been demonstrated to be consistent with energetic precipitation modeling derived from empirical models of field-aligned wave power across a wide-swath of local-time sectors. However, such modeling could not explain the intense, relativistic electron precipitation observed on the nightside. Therefore, this study aims to additionally consider the contributions of three modifications – wave obliquity, frequency spectrum, and local plasma density – to explain this discrepancy on the nightside. By incorporating these effects into both test particle simulations and quasi-linear diffusion modeling, we find that realistic implementations of each individual modification result in only slight changes to the electron precipitation spectrum. However, these modifications, when combined, enable more accurate modeling of ELFIN-observed spectra. In particular, a significant reduction in plasma density enables lower frequency waves, oblique, or even quasi-field aligned waves to resonate with near $\sim1$ MeV electrons closer to the equator. We demonstrate that the levels of modification required to accurately reproduce the nightside spectra of whistler-mode wave-driven relativistic electron precipitation match empirical expectations, and should therefore be included in future radiation belt modeling.