Radiation belt electrons undergo frequent acceleration, transport, and loss processes under various physical mechanisms. One of the most prevalent mechanisms is radial diffusion, caused by the resonant interactions between energetic electrons and ULF waves in the Pc4‐5 band. An indication of this resonant interaction is believed to be the appearance of periodic flux oscillations. In this study, we report long‐lasting, drift‐periodic flux oscillations of relativistic and ultrarelativistic electrons with energies up to ∼7.7 MeV in the outer radiation belt, observed by the Van Allen Probes mission. During this March 2017 event, multi‐MeV electron flux oscillations at the electron drift frequency appeared coincidently with enhanced Pc5 ULF wave activity and lasted for over 10 h in the center of the outer belt. The amplitude of such flux oscillations is well correlated with the radial gradient of electron phase space density (PSD), with almost no oscillation observed near the PSD peak. The temporal evolution of the PSD radial profile also suggests the dominant role of radial diffusion in multi‐MeV electron dynamics during this event. By combining these observations, we conclude that these multi‐MeV electron flux oscillations are caused by the resonant interactions between electrons and broadband Pc5 ULF waves and are an indicator of the ongoing radial diffusion process during this event. They contain essential information of radial diffusion and have the potential to be further used to quantify the radial diffusion effects and aid in a better understanding of this prevailing mechanism.
Multi‐MeV electron drift‐periodic flux oscillations observed in Earth's radiation belts indicate radial transport and energization/de‐energization of these radiation belt core populations. Using multi‐year Van Allen Probes observations, a statistical analysis is conducted to understand the characteristics of this phenomenon. The results show that most of these flux oscillations result from resonant interactions with broadband ultralow frequency (ULF) waves and are indicators of ongoing radial diffusion. The occurrence frequency of flux oscillations is higher during high solar wind speed/dynamic pressure and geomagnetically active times; however, a large number of them were still observed under mild to moderate solar wind/geomagnetic conditions. The occurrence frequency is also highest (up to ∼30%) at low L‐shells (
- Award ID(s):
- 2140933
- NSF-PAR ID:
- 10374419
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 7
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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