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Abstract We investigate the dynamics of relativistic electrons in the Earth's outer radiation belt by analyzing the interplay of several key physical processes: electron losses due to pitch angle scattering from electromagnetic ion cyclotron (EMIC) waves and chorus waves, and electron flux increases from chorus wave‐driven acceleration of 100–300 keV seed electrons injected from the plasma sheet. We examine a weak geomagnetic storm on 17 April 2021, using observations from various spacecraft, including GOES, Van Allen Probes, ERG/ARASE, MMS, ELFIN, and POES. Despite strong EMIC‐ and chorus wave‐driven electron precipitation in the outer radiation belt, trapped 0.1–1.5 MeV electron fluxes actually increased. We use theoretical estimates of electron quasi‐linear diffusion rates by chorus and EMIC waves, based on statistics of their wave power distribution, to examine the role of those waves in the observed relativistic electron flux variations. We find that a significant supply of 100–300 keV electrons by plasma sheet injections together with chorus wave‐driven acceleration can overcome the rate of chorus and EMIC wave‐driven electron losses through pitch angle scattering toward the loss cone, explaining the observed net increase in electron fluxes. Our study emphasizes the importance of simultaneously taking into account resonant wave‐particle interactions and modeled local energy gradients of electron phase space density following injections, to accurately forecast the dynamical evolution of trapped electron fluxes.
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The Combined Influence of Lower Band Chorus and ULF Waves on Radiation Belt Electron Fluxes at Individual L ‐Shells
Abstract We investigate the timing and relative influence of VLF in the chorus frequency range observed by the DEMETER spacecraft and ULF wave activity from ground stations on daily changes in electron flux (0.23 to over 2.9 MeV) observed by the HEO‐3 spacecraft. At eachL‐shell, we use multiple regression to investigate the effects of each wave type and each daily lag independent of the others. We find that reduction and enhancement of electrons occur at different timescales. Chorus power spectral density and ULF wave power are associated with immediate electron decreases on the same day but with flux enhancement 1–2 days later. ULF is nearly always more influential than chorus on both increases and decreases of flux, although chorus is often a significant factor. There was virtually no difference in correlations of ULF Pc3, Pc4, or Pc5 with electron flux. A synergistic interaction between chorus and ULF waves means that enhancement is most effective when both waves are present, pointing to a two‐step process where local acceleration by chorus waves first energizes electrons which are then brought to even higher energies by inward radial diffusion due to ULF waves. However, decreases in flux due to these waves act additively. Chorus and ULF waves combined are most effective at describing changes in electron flux at >1.5 MeV. At lowerL(2–3), correlations between ULF and VLF (likely hiss) with electron flux were low. The most successful models, overL = 4–6, explained up to 47.1% of the variation in the data.
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- PAR ID:
- 10366947
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 126
- Issue:
- 5
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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