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Title: Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt

Using observations from NASA's Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important—and potentially dominant—source of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for ≥100 keV. After SPELLS events, the slot region reforms due to slow energy-dependentmore » decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Altogether, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an “on/off,” geomagnetic-activity-dependent source from higher radial distances.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [2] ;  [3] ; ORCiD logo [4] ; ORCiD logo [5] ; ORCiD logo [5]
  1. The Aerospace Corp., El Segundo, CA (United States)
  2. Univ. of Colorado, Boulder, CO (United States)
  3. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  4. The Johns Hopkins Univ., Laurel, MD (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-17-20874
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Volume: 122; Journal Issue: 1; 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); USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Heliospheric and Magnetospheric Physics
OSTI Identifier:
1345952

Turner, Drew Lawson, O'Brien, T. P., Fennell, J. F., Claudepierre, S. G., Blake, J. B., Jaynes, A. N., Baker, D. N., Kanekal, S., Gkioulidou, M., Henderson, Michael Gerard, and Reeves, Geoffrey D.. Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt. United States: N. p., Web. doi:10.1002/2016JA023600.
Turner, Drew Lawson, O'Brien, T. P., Fennell, J. F., Claudepierre, S. G., Blake, J. B., Jaynes, A. N., Baker, D. N., Kanekal, S., Gkioulidou, M., Henderson, Michael Gerard, & Reeves, Geoffrey D.. Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt. United States. doi:10.1002/2016JA023600.
Turner, Drew Lawson, O'Brien, T. P., Fennell, J. F., Claudepierre, S. G., Blake, J. B., Jaynes, A. N., Baker, D. N., Kanekal, S., Gkioulidou, M., Henderson, Michael Gerard, and Reeves, Geoffrey D.. 2017. "Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt". United States. doi:10.1002/2016JA023600. https://www.osti.gov/servlets/purl/1345952.
@article{osti_1345952,
title = {Investigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt},
author = {Turner, Drew Lawson and O'Brien, T. P. and Fennell, J. F. and Claudepierre, S. G. and Blake, J. B. and Jaynes, A. N. and Baker, D. N. and Kanekal, S. and Gkioulidou, M. and Henderson, Michael Gerard and Reeves, Geoffrey D.},
abstractNote = {Using observations from NASA's Van Allen Probes, we study the role of sudden particle enhancements at low L shells (SPELLS) as a source of inner radiation belt electrons. SPELLS events are characterized by electron intensity enhancements of approximately an order of magnitude or more in less than 1 day at L < 3. During quiet and average geomagnetic conditions, the phase space density radial distributions for fixed first and second adiabatic invariants are peaked at 2 < L < 3 for electrons ranging in energy from ~50 keV to ~1 MeV, indicating that slow inward radial diffusion is not the dominant source of inner belt electrons under quiet/average conditions. During SPELLS events, the evolution of electron distributions reveals an enhancement of phase space density that can exceed 3 orders of magnitude in the slot region and continues into the inner radiation belt, which is evidence that these events are an important—and potentially dominant—source of inner belt electrons. Electron fluxes from September 2012 through February 2016 reveal that SPELLS occur frequently (~2.5/month at 200 keV), but the number of observed events decreases exponentially with increasing electron energy for ≥100 keV. After SPELLS events, the slot region reforms due to slow energy-dependent decay over several day time scales, consistent with losses due to interactions with plasmaspheric hiss. Altogether, these results indicate that the peaked phase space density distributions in the inner electron radiation belt result from an “on/off,” geomagnetic-activity-dependent source from higher radial distances.},
doi = {10.1002/2016JA023600},
journal = {Journal of Geophysical Research. Space Physics},
number = 1,
volume = 122,
place = {United States},
year = {2017},
month = {1}
}