A feature of Earth's storm‐time magnetosphere outside the plasmapause is the occurrence of broad‐spectrum Alfvénic fluctuations. In this letter observations from the Van Allen Probes are compared with 3‐D fluid‐kinetic simulations of an evolving convective flow channel to investigate the mechanisms generating the observed spectrum. It is shown how narrow channels of fast convection are unstable to the Kelvin‐Helmholtz instability which on closed field‐lines initiates a cascade to small scales. Sustained driving of the flow combined with reflection from the topside ionosphere leads to the generation of an intensified spectrum of electromagnetic structures having similar spectral and morphological characteristics to those observed. This process couples enhanced magnetospheric convection to kinetic scale electromagnetic fluctuations that drive particle transport, scattering and energization through the outer radiation belt and ring current during geomagnetic storms.
- Award ID(s):
- 2013433
- NSF-PAR ID:
- 10335041
- Date Published:
- Journal Name:
- Frontiers in Astronomy and Space Sciences
- Volume:
- 8
- ISSN:
- 2296-987X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Using 5‐year of measurements from Van Allen Probes, we present a survey of the statistical dependence of the Earth's outer radiation belt electron flux dropouts during geomagnetic storms on electron energy and various driving parameters including interplanetary magnetic field Bz, PSW, SYM‐H, and AE. By systematically investigating the dropouts over energies of 1 keV–10 MeV at L‐shells spanning 4.0–6.5, we find that the dropouts are naturally divided into three regions. The dropouts show much higher occurrence rates at energies below ∼100 keV and above ∼1 MeV compared to much smaller occurrence rate at intermediate energies around hundreds of keV. The flux decays more dramatically at energies above ∼1 MeV compared to the energies below ∼100 keV. The flux dropouts of electrons below ∼100 keV strongly depend on magnetic local time (MLT), which demonstrate high occurrence rates on the nightside (18–06 MLT), with the highest occurrence rate associated with northward Bz, strong PSWand SYM‐H, and weak AE conditions. The strongest flux decay of these dropouts is found on the nightside, which strongly depends on PSWand SYM‐H. However, there is no clear MLT dependence of the occurrence rate of relativistic electron flux dropouts above ∼1 MeV, but the flux decay of these dropouts is more significant on the dayside, with stronger decay associated with southward IMF Bz, strong PSW, SYM‐H, and AE conditions. Our statistical results are crucial for understanding of the fundamental physical mechanisms that control the outer belt electron dynamics and developing future potential radiation belt forecasting capability.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fspas.2021.728531
