Physical mechanism causing rapid changes in ultrarelativistic electron pitch angle distributions right after a shock arrival: Evaluation of an electron dropout event
Abstract
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 (>1 MeV) 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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Sep 01, 2016
- Source ID
- 10.1002/2016ja022517
Entities
People
- Craig Kletzing
- Daniel N. Baker
- Geoffrey D Reeves
- George G. Hospodarsky
- Harlan Spence
- J. B. Blake
- J. Bortnik
- Jiang Li
- Joseph F. Fennell
- Larry Chen
- Qianli Ma
- R. M. Thorne
- V. Angelopoulos
- Wen Li
- William S. Kurth
- Xiao-Jia Zhang
- Yukitoshi Nishimura
Organizations
- Air Force Office of Scientific Research
- Boston University
- Johns Hopkins University Applied Physics Laboratory
- Los Alamos National Laboratory
- National Aeronautics and Space Administration
- National Science Foundation
- The Aerospace Corporation
- University of California, Los Angeles
- University of Iowa
- University of New Hampshire
- University of Texas at Dallas