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Abstract Man‐made very low frequency (VLF) transmitter waves play a critical role in energetic electron scattering and precipitation from the inner radiation belt, a type of which is called wisp precipitation. Wisps exhibit dispersive energy‐versus‐Lspectra due to the evolution of electron cyclotron resonance conditions with near‐monochromatic VLF transmitter waves. Here, we report on such observations of inner belt wisp precipitation events with full pitch angle resolution in the energy range of 50 to ∼500 keV as measured by Electron Loss and Fields Investigation (ELFIN) atL < ∼2 between March 2021 and April 2022. Statistical observations (82 events) reveal occasional (18 events) wisp precipitation events with local bounce‐loss‐cone electron flux enhancements, which provide new information compared with flux enhancements measured in previous studies only in the drift loss cone. Based on magnetic field and plasmaspheric density models, quasilinear theory, and detailed pitch angle distributions of wisps from ELFIN, we have estimated the wisp electron bounce‐averaged pitch angle diffusion coefficients to be of the order of 10−4to 10−2 s−1. These are several orders of magnitude larger than the diffusion rates calculated from models using global statistical averages of VLF transmitter wave power. When using our estimated diffusion coefficients to deduce the associated local transmitter wave amplitudes near the equator, based on quasilinear calculations from a transmitter‐induced electron diffusion model, we find these wave amplitudes to be >1 mV/m. Although probable overestimates, such inferred wave amplitudes exceed the theoretical threshold amplitude for nonlinear interactions, strongly suggesting that it is necessary to include nonlinear effects for an accurate evaluation of energetic electron scattering by transmitter waves.
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Electron Lifetimes and Diffusion Rates Inferred From ELFIN Measurements at Low Altitude: First Results
Abstract In the radiation belts, energetic and relativistic electron precipitation into the atmosphere is expected to be mainly controlled over the long term by quasilinear pitch‐angle scattering by whistler‐mode and electromagnetic ion cyclotron waves. Accordingly, statistical electron lifetimes have been derived from quasilinear diffusion theory on the basis of multi‐year wave statistics. However, the full consistency of such statistical quasilinear models of electron lifetimes with both measured electron lifetimes, spectra of trapped and precipitated electron fluxes, and wave‐driven diffusion rates inferred from electron flux measurements, has not yet been verified in detail. In the present study, we use data from Electron Loss and Fields Investigation (ELFIN) mission CubeSats, launched in September 2018 in low Earth orbit, to carry out such comparisons between quasi‐linear diffusion theory and observed electron flux variations. We show that statistical theoretical lifetime models are in reasonable agreement with electron pitch‐angle diffusion rates inferred from the precipitated to trapped 100 keV electron flux ratio measured by ELFIN after correction for atmospheric backscatter, as well as with timescales of trapped electron flux decay independently measured over several days by ELFIN. The present results demonstrate for the first time a broad consistency between timescales of trapped electron flux decay, the pitch‐angle distribution of precipitated electrons, and quasilinear models of wave‐driven electron loss, showing the reliability of such statistical electron lifetime models parameterized by geomagnetic activity for evaluating electron precipitation into the atmosphere during not too disturbed periods.
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- PAR ID:
- 10375567
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 126
- Issue:
- 11
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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