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Title: Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event: Drift Shell Splitting on the Dayside

Three mechanisms have been proposed to explain relativistic electron flux depletions (dropouts) in the Earth's outer radiation belt during storm times: adiabatic expansion of electron drift shells due to a decrease in magnetic field strength, magnetopause shadowing and subsequent outward radial diffusion, and precipitation into the atmosphere (driven by EMIC wave scattering). Which mechanism predominates in causing electron dropouts commonly observed in the outer radiation belt is still debatable. In the present study, we evaluate the physical mechanism that may be primarily responsible for causing the sudden change in relativistic electron pitch angle distributions during a dropout event observed by Van Allen Probes during the main phase of the 27 February 2014 storm. During this event, the phase space density of ultrarelativistic (>1MeV) electrons was depleted by more than 1 order of magnitude over the entire radial extent of the outer radiation belt (3 < L* < 5) in less than 6 h after the passage of an interplanetary shock. We model the electron pitch angle distribution under a compressed magnetic field topology based on actual solar wind conditions. Although these ultrarelativistic electrons exhibit highly anisotropic (peaked in 90°), energy-dependent pitch angle distributions, which appear to be associated with themore » typical EMIC wave scattering, comparison of the modeled electron distribution to electron measurements indicates that drift shell splitting is responsible for this rapid change in electron pitch angle distributions. This further indicates that magnetopause loss is the predominant cause of the electron dropout right after the shock arrival.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ; ORCiD logo [3] ;  [3] ;  [3] ;  [3] ;  [5] ;  [6] ; ORCiD logo [7] ;  [8] ;  [9] ;  [9] ;  [9] ;  [10] ;  [10]
  1. Univ. of California, Los Angeles, CA (United States). Dept. of Atmospheric and Oceanic Sciences; Univ. of California, Los Angeles, CA (United States). Dept. of Earth, Planetary, and Space Sciences and Inst. of Geophysics and Space Physics
  2. Univ. of California, Los Angeles, CA (United States). Dept. of Atmospheric and Oceanic Sciences; Boston Univ., MA (United States). Center for Space Physics
  3. Univ. of California, Los Angeles, CA (United States). Dept. of Atmospheric and Oceanic Sciences
  4. Univ. of California, Los Angeles, CA (United States). Dept. of Earth, Planetary, and Space Sciences and Inst. of Geophysics and Space Physics
  5. Univ. of Texas at Dallas, Richardson, TX (United States). Dept. of Physics
  6. Univ. of Colorado, Boulder, CO (United States). Lab. for Atmospheric and Space Research
  7. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States). Space Sciences Division
  8. Univ. of New Hampshire, Durham, NH (United States). Inst. for the Study of Earth, Oceans, and Space
  9. Univ. of Iowa, Iowa City, IA (United States). Dept. of Physics and Astronomy
  10. Aerospace Corporation, Los Angeles, CA (United States)
Publication Date:
Report Number(s):
LA-UR-16-23134
Journal ID: ISSN 2169-9380; TRN: US1703008
Grant/Contract Number:
AC52-06NA25396; 967399; 921647; NAS5-01072; FA9550-15-1-0158; NNX15AI96G; NNX15AF61G; NNX11AR64G; NNX13AI61G; NNX14AI18G; AGS 1405041; 1405054; 1564510
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 9; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
National Aeronautic and Space Administration (NASA); National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Heliospheric and Magnetospheric Physics; dropouts; relativistic electron loss; drift shell splitting; magnetopause shadowing; outer radiation belt; magnetic storm
OSTI Identifier:
1402610