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Abstract Electron losses from the outer radiation belt are typically attributed to resonant electron scattering by whistler‐mode waves. Although the quasi‐linear diffusive regime of such scattering is well understood, the observed waves are often quite intense and in the nonlinear regime of resonant wave‐particle interaction. Such nonlinear resonant interactions are still being actively studied due to their potential for driving fast precipitation. However, direct observations of nonlinear resonance of whistler‐mode waves with electron distributions are scarce. Here, we present evidence for such resonance with high‐resolution electron energy and pitch angle spectra acquired at low‐altitudes by the dual Electron Losses and Fields INvestgation (ELFIN) CubeSats combined with conjugate measurements of equatorial plasma parameters, wave properties, and electron energy spectra by the Time History of Events and Macroscale Interactions during Substorms and Magnetospheric MultiScale missions. ELFIN has obtained numerous conjunction events exhibiting whistler wave driven precipitation; in this study, we present two such events which epitomize signatures of nonlinear resonant scattering. A test particle simulation of electron interactions with intense whistler‐mode waves prescribed at the equator is employed to directly compare modeled precipitation spectra with ELFIN observations. We show that the observed precipitating spectra match expectations to within observational uncertainties of wave amplitude for reasonable assumptions of wave power distribution along the magnetic field line. These results indicate the importance of nonlinear resonant effects when describing intense precipitation patterns of energetic electrons and open the possibility of remotely investigating equatorial wave properties using just properties of precipitation energy and pitch angle spectra.
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This content will become publicly available on April 18, 2026
Whistler Mode Wave‐Driven Electron Scattering Properties From ELFIN Measurements of the Precipitation Ratio
Abstract Whistler‐mode chorus and hiss waves play an important role in Earth's radiation belt electron dynamics. Direct measurements of whistler wave‐driven electron precipitation and the resultant pitch angle distribution were previously limited by the insufficient resolution of low Earth orbit satellites. In this study, we use recent measurements from the Electron Losses and Fields INvestigation CubeSats, which provide energy‐ and pitch angle‐resolved electron distributions to statistically evaluate electron scattering properties driven by whistler waves. Our survey indicates that events with increasing precipitating‐to‐trapped flux ratios (evaluated at 63 keV unless otherwise specified) correlate with increasing trapped flux at energies up to ∼750 keV. Weak precipitation events (precipitation ratio <0.2) are evenly distributed, while stronger precipitation events tend to be concentrated atL > 5 over midnight‐to‐noon local times during disturbed geomagnetic conditions. These results are crucial for characterizing the whistler‐mode wave driven electron scattering properties and evaluating its impact on the ionosphere.
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- PAR ID:
- 10593998
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 130
- Issue:
- 4
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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