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Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms

Thorne R. M., Y. Y. Shprits, N. P. Meredith, R. B. Horne, W. Li, L. R. Lyons, (2007), Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms, J. of Geophys. Res. [Space Physics], 112, doi:10.1029/2006JA012176

Abstract

Energetic electrons (≥50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies but does not explain the rapid appearance of higher-energy electrons (≥150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200–700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot and prevents acceleration to energies higher than ∼700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies ≥1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by electromagnetic ion cyclotron waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi-MeV energies at locations normally associated with the slot.

Authors (sorted by name)

Horne Li Lyons Meredith Shprits Thorne

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was funded in part by NASA grant NNG04GN44G and NSF GEM grants ATM‐0402615 and ATM‐0603191. The authors thank R. Anderson for use of CRRES wave data and S. Liu for assistance with Figure 2.

Grants

ATM‐0402615 ATM‐0603191 NNG04GN44G

Bibtex

@article{doi:10.1029/2006JA012176,
author = {Thorne, R. M. and Shprits, Y. Y. and Meredith, N. P. and Horne, R. B. and Li, W. and Lyons, L. R.},
title = {Refilling of the slot region between the inner and outer electron radiation belts during geomagnetic storms},
journal = {Journal of Geophysical Research: Space Physics},
volume = {112},
year = {2007},
number = {A6},
pages = {},
keywords = {radiation belt slot, wave acceleration},
doi = {10.1029/2006JA012176},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2006JA012176},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2006JA012176},
abstract = {Energetic electrons (≥50 keV) are injected into the slot region (2 < L < 4) between the inner and outer radiation belts during the early recovery phase of geomagnetic storms. Enhanced convection from the plasma sheet can account for the storm-time injection at lower energies but does not explain the rapid appearance of higher-energy electrons (≥150 keV). The effectiveness of either radial diffusion (driven by enhanced ULF waves) or local acceleration (during interactions with enhanced whistler mode chorus emissions), as a potential source for refilling the slot at higher energies, is analyzed for observed conditions during the early recovery phase of the 10 October 1990 storm. We demonstrate that local acceleration, driven by observed chorus emissions, can account for the rapid enhancement in 200–700 keV electrons in the outer slot region near L = 3.3. Radial diffusion is much less effective but may partially contribute to the flux enhancement at lower L. Subsequent outward expansion of the plasmapause during the storm recovery phase effectively terminates local wave acceleration in the slot and prevents acceleration to energies higher than ∼700 keV. A statistical analysis of energetic electron flux enhancements and wave and plasma properties over the entire CRRES mission supports the concept of local wave acceleration as a dominant process for refilling the slot during the main and early recovery phase of storms. For moderate storms, the injection process naturally becomes less effective at energies ≥1 MeV, due to the longer wave acceleration times and additional precipitation loss from scattering by electromagnetic ion cyclotron waves. However, during extreme events when the plasmapause remains compressed for several days, conditions may occur to allow wave acceleration to multi-MeV energies at locations normally associated with the slot.}
}