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Radial gradients of phase space density in the inner electron radiation

Kim K., Y. Shprits, (2012), Radial gradients of phase space density in the inner electron radiation, J. of Geophys. Res. [Space Physics], 117, doi:10.1029/2012JA018211

Abstract

While the outer radiation belt (3.5 L 8.0) is highly variable with respect to geomagnetic activity, the inner radiation belt (1.2 L 2.0) is relatively stable. Less attention has been paid to the inner electron belt in recent years. It has been generally accepted that the equilibrium structure of radiation belt electrons is explained by the slow inward radial diffusion from a source in the outer belt and losses by Coulomb collision and wave-particle interaction. In this study, we examine this well accepted theory using the radial profiles of the phase space density (PSD), inferred from in situ measurements made by three different satellites: S3–3, CRRES, and POLAR. Our results show that electron PSD in the inner electron belt has a clear prominent local peak and negative radial gradient in the outer portion of the inner zone, i.e., decreasing PSD with increasingL-value. A likely explanation for the peaks in PSD is acceleration due to energy diffusion produced by lightning-generated and anthropogenic whistlers. These results indicate that either additional local acceleration mechanism is responsible for the formation of the inner electron belt or inner electron belt is formed by sporadic injections of electrons into the inner zone. The currently well accepted model of slow diffusion and losses will be further examined by the upcoming Radiation Belt Storm Probes (RBSP) mission.

Authors (sorted by name)

Kim Shprits

Journal / Conference

Journal Of Geophysical Research (Space Physics)

Acknowledgments

Authors would like to thanks Joe Fennell and Paul O'Brian for useful discussions. We are grateful to Reiner Friedel who provided the POLAR/CEPPAD data. This research was supported by NASA under grants NNX09AF51G 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. We would also like to thank Bob Weigel and Bob Johnston for providing data.

Grants

NNX09AF51G NNX10AK996

Bibtex

@article{doi:10.1029/2012JA018211,
author = {Kim, Kyung-Chan and Shprits, Yuri},
title = {Radial gradients of phase space density in the inner electron radiation},
journal = {Journal of Geophysical Research: Space Physics},
volume = {117},
year = {2012},
number = {A12},
pages = {},
keywords = {inner electron radiation belt},
doi = {10.1029/2012JA018211},
url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2012JA018211},
eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012JA018211},
abstract = {While the outer radiation belt (3.5   L   8.0) is highly variable with respect to geomagnetic activity, the inner radiation belt (1.2   L  2.0) is relatively stable. Less attention has been paid to the inner electron belt in recent years. It has been generally accepted that the equilibrium structure of radiation belt electrons is explained by the slow inward radial diffusion from a source in the outer belt and losses by Coulomb collision and wave-particle interaction. In this study, we examine this well accepted theory using the radial profiles of the phase space density (PSD), inferred from in situ measurements made by three different satellites: S3–3, CRRES, and POLAR. Our results show that electron PSD in the inner electron belt has a clear prominent local peak and negative radial gradient in the outer portion of the inner zone, i.e., decreasing PSD with increasingL-value. A likely explanation for the peaks in PSD is acceleration due to energy diffusion produced by lightning-generated and anthropogenic whistlers. These results indicate that either additional local acceleration mechanism is responsible for the formation of the inner electron belt or inner electron belt is formed by sporadic injections of electrons into the inner zone. The currently well accepted model of slow diffusion and losses will be further examined by the upcoming Radiation Belt Storm Probes (RBSP) mission.}
}