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

TitleInvestigating the source of near-relativistic and relativistic electrons in Earth's inner radiation belt
Publication TypeJournal Article
Year of Publication2016
AuthorsTurner, DL, O'Brien, TP, Fennell, JF, Claudepierre, SG, Blake, JB, Jaynes, AN, Baker, DN, Kanekal, S, Gkioulidou, M, Henderson, MG, Reeves, GD
JournalJournal of Geophysical Research: Space Physics
Date Published12/2016
Keywords2720 Energetic Particles, trapped; 2730 Magnetosphere: inner; 2774 Radiation belts; 7807 Charged particle motion and acceleration; 7984 Space radiation environment; energetic particle injections; inner magnetosphere; Radiation belts; relativistic electrons; Van Allen Probes
AbstractUsing 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 one 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 three 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 timescales, consistent with losses due to interactions with plasmaspheric hiss. Combined, 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.
Short TitleJ. Geophys. Res. Space Physics

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