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Title: Understanding the mechanisms of radiation belt dropouts observed by Van Allen Probes

Abstract

To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of radiation belt electrons, three distinct radiation belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and the μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Here, our findings suggest that these radiation belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* < 4, while EMIC waves can efficiently scatter electrons at L* > 4. Compared to the magnetopause standoff position, it is more reliable to use LCDSmore » to evaluate the impact of magnetopause shadowing. Finally, the evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer radiation belt.« less

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [3]
  1. Wuhan Univ. (China). School of Electronic Information, Dept. of Space Physics; West Virginia Univ., Morgantown, WV (United States). Dept. of Physics and Astronomy
  2. West Virginia Univ., Morgantown, WV (United States). Dept. of Physics and Astronomy
  3. Univ. of Colorado, Boulder, CO (United States). Lab. for Atmospheric and Space Physics
  4. Wuhan Univ. (China). School of Electronic Information, Dept. of Space Physics
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF); National Aeronautic and Space Administration (NASA); National Natural Science Foundation of China (NNSFC)
OSTI Identifier:
1394980
Alternate Identifier(s):
OSTI ID: 1396068
Report Number(s):
LA-UR-17-24736
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396; AGS-1613081; NNX15AW06G; 41674163; 41474141; 41204120
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 122; Journal Issue: 10; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Heliospheric and Magnetospheric Physics; radiation belt dropout; last closed drift shell; EMIC wave; magnetopause shadowing; phase space density

Citation Formats

Xiang, Zheng, Tu, Weichao, Li, Xinlin, Ni, Binbin, Morley, Steven Karl, and Baker, D. N.. Understanding the mechanisms of radiation belt dropouts observed by Van Allen Probes. United States: N. p., 2017. Web. doi:10.1002/2017JA024487.
Xiang, Zheng, Tu, Weichao, Li, Xinlin, Ni, Binbin, Morley, Steven Karl, & Baker, D. N.. Understanding the mechanisms of radiation belt dropouts observed by Van Allen Probes. United States. doi:10.1002/2017JA024487.
Xiang, Zheng, Tu, Weichao, Li, Xinlin, Ni, Binbin, Morley, Steven Karl, and Baker, D. N.. Wed . "Understanding the mechanisms of radiation belt dropouts observed by Van Allen Probes". United States. doi:10.1002/2017JA024487.
@article{osti_1394980,
title = {Understanding the mechanisms of radiation belt dropouts observed by Van Allen Probes},
author = {Xiang, Zheng and Tu, Weichao and Li, Xinlin and Ni, Binbin and Morley, Steven Karl and Baker, D. N.},
abstractNote = {To achieve a better understanding of the dominant loss mechanisms for the rapid dropouts of radiation belt electrons, three distinct radiation belt dropout events observed by Van Allen Probes are comprehensively investigated. For each event, observations of the pitch angle distribution of electron fluxes and electromagnetic ion cyclotron (EMIC) waves are analyzed to determine the effects of atmospheric precipitation loss due to pitch angle scattering induced by EMIC waves. Last closed drift shells (LCDS) and magnetopause standoff position are obtained to evaluate the effects of magnetopause shadowing loss. Evolution of electron phase space density (PSD) versus L* profiles and the μ and K (first and second adiabatic invariants) dependence of the electron PSD drops are calculated to further analyze the dominant loss mechanisms at different L*. Here, our findings suggest that these radiation belt dropouts can be classified into distinct classes in terms of dominant loss mechanisms: magnetopause shadowing dominant, EMIC wave scattering dominant, and combination of both mechanisms. Different from previous understanding, our results show that magnetopause shadowing can deplete electrons at L* < 4, while EMIC waves can efficiently scatter electrons at L* > 4. Compared to the magnetopause standoff position, it is more reliable to use LCDS to evaluate the impact of magnetopause shadowing. Finally, the evolution of electron PSD versus L* profile and the μ, K dependence of electron PSD drops can provide critical and credible clues regarding the mechanisms responsible for electron losses at different L* over the outer radiation belt.},
doi = {10.1002/2017JA024487},
journal = {Journal of Geophysical Research. Space Physics},
number = 10,
volume = 122,
place = {United States},
year = {Wed Aug 30 00:00:00 EDT 2017},
month = {Wed Aug 30 00:00:00 EDT 2017}
}

Journal Article:
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