Investigating the source of near‐relativistic and relativistic electrons in Earth's inner radiation belt. Issue 1 (30th January 2017)

• Record Type: Journal Article
• Authors: Turner, D. L.; O'Brien, T. P.; Fennell, J. F.; Claudepierre, S. G.; Blake, J. B.; Jaynes, A. N.; Baker, D. N.; Kanekal, S.; Gkioulidou, M.; Henderson, M. G.; Reeves, G. D.
• Is Part Of: Journal of geophysical research. Volume 122:Issue 1(2017)
• Page Start: 695
• Page End: 710
• Publication Date: 2017-01-30
• Subjects: energetic particle injections -- radiation belts -- relativistic electrons -- inner magnetosphere; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2016JA023600
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: 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. 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. Key Points: Phase space density distributions of tens to hundreds of keV electrons in the inner belt are peaked in L* during quiet and average conditions Sudden flux enhancements during active conditions are the dominant source of hundreds of keV electrons in the inner belt The occurrence of sudden flux enhancements at low L is strongly dependent on energy