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Abstract Semi‐empirical coefficients for electron transport in Alfvénic turbulence are used to drive the global evolution of energetic electron distributions through Earth's outer radiation belt. It is shown how these turbulent fields facilitate radial transport and pitch‐angle scattering that drive losses through the magnetopause, into the plasma sheet, through the plasmapause and to the atmosphere. Butterfly distributions are formed due to pitch‐angle scattering and the combined effect of the loss processes. For the observed spectrum of oscillations, it is estimated that Alfvénic turbulence drives order of magnitude depletions of outer radiation belt electron fluxes at relativistic energies over a period of a few hours. On the other hand, at lower energies, energization in transverse Alfvénic electric fields leads to enhancements of the electron spectrum to provide a source population for subsequent acceleration to higher energies and, in concert with the loss processes, provides exponential spectral form as a function of energy.
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Broadband Kinetic Alfvén Waves and the Pitch Angle Distribution of Relativistic Electrons
Abstract A statistical survey using 3 years of Van Allen Probes data from 2013 to 2015 is conducted to investigate the impact of broadband kinetic Alfvén waves (KAWs) on the pitch angle distributions (PADs) of relativistic electrons. 62 events exhibiting distinct KAW signatures, identified when other wave modes known to generate butterfly distributions were absent, are examined along with the corresponding PADs of electrons. The results reveal a relationship between the spectral energy density of KAWs and PAD of relativistic electrons, with butterfly PAD features becoming more pronounced and showing larger dip‐sizes as the spectral energy density of KAWs increases, particularly for electrons in 0.5–3.4 MeV energy range. At these times the magnetopause sub‐solar stand‐off distance renders magnetopause shadowing an unlikely formation mechanism. This suggests the interaction of relativistic electrons with broadband KAWs could be a significant mechanism, alongside drift‐shell splitting, contributing to the formation of butterfly PADs in the night‐side outer radiation belt of Earth.
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- Award ID(s):
- 2041971
- PAR ID:
- 10600156
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 52
- Issue:
- 10
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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