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Title: Source and seed populations for relativistic electrons: Their roles in radiation belt changes

Strong enhancements of outer Van Allen belt electrons have been shown to have a clear dependence on solar wind speed and on the duration of southward interplanetary magnetic field. However, individual case study analyses also have demonstrated that many geomagnetic storms produce little in the way of outer belt enhancements and, in fact, may produce substantial losses of relativistic electrons. In this study, focused upon a key period in August–September 2014, we use GOES geostationary orbit electron flux data and Van Allen Probes particle and fields data to study the process of radiation belt electron acceleration. One particular interval, 13–22 September, initiated by a short-lived geomagnetic storm and characterized by a long period of primarily northward interplanetary magnetic field (IMF), showed strong depletion of relativistic electrons (including an unprecedented observation of long-lasting depletion at geostationary orbit) while an immediately preceding, and another immediately subsequent, storm showed strong radiation belt enhancement. We demonstrate with these data that two distinct electron populations resulting from magnetospheric substorm activity are crucial elements in the ultimate acceleration of highly relativistic electrons in the outer belt: the source population (tens of keV) that give rise to VLF wave growth and the seed population (hundreds of keV)more » that are, in turn, accelerated through VLF wave interactions to much higher energies. ULF waves may also play a role by either inhibiting or enhancing this process through radial diffusion effects. Furthermore, if any components of the inner magnetospheric accelerator happen to be absent, the relativistic radiation belt enhancement fails to materialize.« less
Authors:
 [1] ;  [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [1] ;  [1] ;  [4] ;  [5] ;  [5] ;  [6] ;  [6] ;  [7] ;  [8] ;  [9]
  1. Univ. of Colorado, Boulder, CO (United States)
  2. NOAA Space Weather Prediction Center, Boulder, CO (United States)
  3. Univ. of Colorado, Boulder, CO (United States); NOAA National Centers for Environmental Information, Boulder, CO (United States)
  4. NASA Goddard Space Flight Center, Greenbelt, MD (United States)
  5. Aerospace Corporation, Los Angeles, CA (United States)
  6. Univ. of California, Los Angeles, CA (United States)
  7. Univ. of Iowa, Iowa City, IA (United States)
  8. Univ. of New Hampshire, Durham, NH (United States)
  9. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
OSTI Identifier:
1236779
Report Number(s):
LA-UR--15-27789
Journal ID: ISSN 2169-9380
Grant/Contract Number:
967399; NAS501072; AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 120; Journal Issue: 9; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES radiation belts; Van Allen Probes; relativistic electrons; VLF waves; ULF waves; substorms