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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

Journal Article · · Journal of Geophysical Research. Space Physics
DOI:https://doi.org/10.1002/2016JA022517· OSTI ID:1402610
 [1];  [2];  [3];  [4];  [3];  [3];  [3];  [3];  [5];  [6];  [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)
+ Show Author Affiliations

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 the 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.

Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
National Aeronautic and Space Administration (NASA); National Science Foundation (NSF); US Air Force Office of Scientific Research (AFOSR)
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1402610
Report Number(s):
LA-UR--16-23134
Journal Information:
Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 9 Vol. 121; ISSN 2169-9380
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (5)

Statistical distribution of EMIC wave spectra: Observations from Van Allen Probes: STATISTICS ON EMIC WAVE SPECTRA journal December 2016
Radiation Belt “Dropouts” and Drift‐Bounce Resonances in Broadband Electromagnetic Waves journal March 2018
Rapid Loss of Radiation Belt Relativistic Electrons by EMIC Waves journal October 2017
Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes journal October 2017
What Fraction of the Outer Radiation Belt Relativistic Electron Flux at L ≈ 3‐4.5 Was Lost to the Atmosphere During the Dropout Event of the St. Patrick's Day Storm of 2015? journal November 2019

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Related Subjects

58 GEOSCIENCES
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Heliospheric and Magnetospheric Physics
drift shell splitting
dropouts
magnetic storm
magnetopause shadowing
outer radiation belt
relativistic electron loss