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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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Chorus and Hiss Scales in the Inner Magnetosphere: Statistics From High‐Resolution Filter Bank (FBK) Van Allen Proves Multi‐Point Measurements
Abstract The spatial scales of whistler‐mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave‐particle interactions affecting the dynamics of the radiation belts. We use multi‐point wave measurements by two Van Allen Probes in 2013–2019 covering all MLTs atL = 2–6 to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time‐domain correlation technique to the spacecraft approaches closer than 1,000 km, which happened every 70 days in 2012–2018 and every 35 days in 2018–2019. The correlation of chorus wave power dynamics using is found to remain significant up to inter‐spacecraft separations of 400–750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly shows the reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at largerL > 6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (atL < 6) than at higher L‐shells.
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- Award ID(s):
- 1914670
- PAR ID:
- 10369958
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 126
- Issue:
- 7
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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