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Relativistic radiation belt electron responses to GEM magnetic storms: Comparison of CRRES observations with 3-D VERB simulations

Kim K., Y. Shprits, D. Subbotin, B. Ni, (2012), Relativistic radiation belt electron responses to GEM magnetic storms: Comparison of CRRES observations with 3-D VERB simulations, J. of Geophys. Res. [Space Physics], 117, doi:10.1029/2011JA017460

Abstract

Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in-depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time-dependent 3-D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch angle scattering by plasmaspheric hiss inside the plasmasphere. The 3-D VERB simulations show that during the storm main phase and early recovery phase the estimated plasmapause is located deep in the inner region, indicating that pitch angle scattering by chorus waves can be a dominant loss process in the outer belt. We have also confirmed the important role played by mixed energy-pitch angle diffusion by chorus waves, which tends to reduce the fluxes enhanced by local acceleration, resulting in comparable levels of computed and measured fluxes. However, we cannot reproduce the more pronounced flux dropout near the boundary of our simulations during the main phase, which indicates that non-adiabatic losses may extend toL-shells lower than our simulation boundary. We also provide a detailed description of simulations for each of the GEM storm events.

Authors (sorted by name)

Kim Ni Shprits Subbotin

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

This research was supported by NASA under grants NNX09AF51G, NNX10AQ51G, and NNX10AK996 and by the Lab Fees Research Program. K.‐C. Kim was supported by the Study of Near‐Earth Effects by CME/HSS Project and basic research funding from KASI.

Grants

NNX09AF51G NNX10AK996 NNX10AQ51G

Bibtex

@article{doi:10.1029/2011JA017460,
author = {Kim, Kyung-Chan and Shprits, Yuri and Subbotin, Dmitriy and Ni, Binbin},
title = {Relativistic radiation belt electron responses to GEM magnetic storms: Comparison of CRRES observations with 3-D VERB simulations},
year = {2012},
journal = {Journal of Geophysical Research: Space Physics},
volume = {117},
number = {A8},
pages = {},
keywords = {GEM magnetic storms, storm time relativistic electron, wave-particle interaction},
doi = {10.1029/2011JA017460},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2011JA017460},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JA017460},
abstract = {Understanding the dynamics of relativistic electron acceleration, loss, and transport in the Earth's radiation belt during magnetic storms is a challenging task. The U.S. National Science Foundation's Geospace Environment Modeling (GEM) has identified five magnetic storms for in-depth study that occurred during the second half of the Combined Release and Radiation Effects Satellite (CRRES) mission in the year 1991. In this study, we show the responses of relativistic radiation belt electrons to the magnetic storms by comparing the time-dependent 3-D Versatile Electron Radiation Belt (VERB) simulations with the CRRES MEA 1 MeV electron observations in order to investigate the relative roles of the competing effects of previously proposed scattering mechanisms at different storm phases, as well as to examine the extent to which the simulations can reproduce observations. The major scattering processes in our model are radial transport due to Ultra Low Frequency (ULF) electromagnetic fluctuations, pitch angle and energy diffusion including mixed diffusion by whistler mode chorus waves outside the plasmasphere, and pitch angle scattering by plasmaspheric hiss inside the plasmasphere. The 3-D VERB simulations show that during the storm main phase and early recovery phase the estimated plasmapause is located deep in the inner region, indicating that pitch angle scattering by chorus waves can be a dominant loss process in the outer belt. We have also confirmed the important role played by mixed energy-pitch angle diffusion by chorus waves, which tends to reduce the fluxes enhanced by local acceleration, resulting in comparable levels of computed and measured fluxes. However, we cannot reproduce the more pronounced flux dropout near the boundary of our simulations during the main phase, which indicates that non-adiabatic losses may extend toL-shells lower than our simulation boundary. We also provide a detailed description of simulations for each of the GEM storm events.}
}