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Abstract Electron precipitation by chorus whistler‐mode waves generated by the same electron population is expected to play an important role in the dynamics of the outer radiation belt, potentially setting a hard upper limit on trapped energetic electron fluxes. Here, we statistically analyze the relationship between equatorial electron fluxes and the power of mid‐latitude cyclotron‐resonant chorus waves precipitating these electrons, both inferred from ELFIN low‐altitude energy and pitch‐angle resolved electron flux measurements in 2020–2022. We provide clear evidence of a flux limitation coinciding with an exponential increase of precipitation. We statistically demonstrate that the actual inferred resonant wave power gains are well correlated with theoretical linear gains, as in the classical Kennel‐Petschek model, for moderately high linear gains and high fluxes. However, we also find a finite occurrence of very high fluxes, corresponding to resonant waves of moderate average amplitude, implying a softer, more dynamical upper limit than traditionally envisioned.
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Superfast precipitation of energetic electrons in the radiation belts of the Earth
Abstract Energetic electron precipitation from Earth’s outer radiation belt heats the upper atmosphere and alters its chemical properties. The precipitating flux intensity, typically modelled using inputs from high-altitude, equatorial spacecraft, dictates the radiation belt’s energy contribution to the atmosphere and the strength of space-atmosphere coupling. The classical quasi-linear theory of electron precipitation through moderately fast diffusive interactions with plasma waves predicts that precipitating electron fluxes cannot exceed fluxes of electrons trapped in the radiation belt, setting an apparent upper limit for electron precipitation. Here we show from low-altitude satellite observations, that ~100 keV electron precipitation rates often exceed this apparent upper limit. We demonstrate that such superfast precipitation is caused by nonlinear electron interactions with intense plasma waves, which have not been previously incorporated in radiation belt models. The high occurrence rate of superfast precipitation suggests that it is important for modelling both radiation belt fluxes and space-atmosphere coupling.
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- PAR ID:
- 10348620
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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In the Earth's radiation belts, an upper limit on the electron flux is expected to be imposed by the Kennel-Petschek mechanism, through the generation of exponentially more intense whistler-mode waves as the trapped flux increases above this upper limit, leading to fast electron pitch-angle diffusion and precipitation into the atmosphere. Here, we examine a different upper limit, corresponding to a dynamical equilibrium in the presence of energetic electron injections and both pitch-angle and energy diffusion by whistler-mode chorus waves. We first show that during sustained injections, the electron flux energy spectrum tends toward a steady-state attractor resulting from combined chorus wave-driven energy and pitch-angle diffusion. We derive simple analytical expressions for this steady-state energy spectrum in a wide parameter range, in agreement with simulations. Approximate analytical expressions for the corresponding equilibrium upper limit on the electron flux are provided as a function of the strength of energetic electron injections from the plasma sheet. The analytical steady-state energy spectrum is also compared with maximum electron fluxes measured in the outer radiation belt during several geomagnetic storms with strong injections, showing a good agreement at 100–600 keV.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s41467-022-29291-8
