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:

Xiang, Zheng  ^[1];

• Search DOE PAGES for author "Xiang, Zheng"
• Search DOE PAGES for ORCID "0000-0002-4899-7917"

Tu, Weichao  ^[2];

• Search DOE PAGES for author "Tu, Weichao"
• Search DOE PAGES for ORCID "0000-0003-4547-3269"

Li, Xinlin  ^[3];

• Search DOE PAGES for author "Li, Xinlin"
• Search DOE PAGES for ORCID "0000-0002-1683-3192"

Ni, Binbin  ^[4];

• Search DOE PAGES for author "Ni, Binbin"
• Search DOE PAGES for ORCID "0000-0001-6644-0728"

Morley, Steven Karl  ^[5];

• Search DOE PAGES for author "Morley, Steven Karl"
• Search DOE PAGES for ORCID "0000-0001-8520-0199"

Baker, D. N.  ^[3]

• Search DOE PAGES for author "Baker, D. N."
• Search DOE PAGES for ORCID "0000-0001-5909-0926"

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+ Show Author Affiliations

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:

Wed Aug 30 00:00:00 EDT 2017

Research Org.:

Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

USDOE Laboratory Directed Research and Development (LDRD) Program; National Science Foundation (NSF); National Aeronautics and Space Administration (NASA); National Natural Science Foundation of China (NSFC)

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:

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