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  • 1
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    Inner Zone and Slot Electron Radial Diffusion Revisited (2016)
    Wiley
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    Publication Date: 2016-07-05
    Description: Using recent data from NASA's Van Allen Probes, we estimate the quiet-time radial diffusion coefficients for electrons in the inner radiation belt ( L  〈 3) with energies from ~50-750 keV. The observations are consistent with dynamics dominated by pitch angle scattering and radial diffusion. We use a coordinate system in which these two modes of diffusion are separable. Then we integrate phase space density over pitch angle to obtain a “bundle content” that is invariant to pitch angle scattering, except for atmospheric loss. We estimate the effective radial diffusion coefficient from the temporal and radial variation of the bundle content. We show that our diffusion coefficients agree well with previously determined values obtained in the 1960s and 1970s, and follow the form one expects for radial diffusion caused by exponentially decaying impulses in the large-scale electrostatic potential
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    A non-storm time enhancement of relativistic electrons in the outer radiation belt (2013)
    Wiley
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    Publication Date: 2013-12-03
    Description: ABSTRACT [1]  Despite the lack of a geomagnetic storm (based on the Dst index), relativistic electron fluxes were enhanced over 2.5 orders of magnitude in the outer radiation belt in 13 hours on January 13-14, 2013. The unusual enhancement was observed by MagEIS, onboard the Van Allen Probes; REPTile, onboard the Colorado Student Space Weather Experiment (CSSWE); and SST, onboard THEMIS. Analyses of MagEIS phase space density (PSD) profiles show a positive outward radial gradient from 4 〈 L 〈 5.5. However, THEMIS observations show a peak in PSD outside of the Van Allen Probes’ apogee, which suggest a very interesting scenario: wave-particle interactions causing a PSD peak at ~ L* = 5.5 from where the electrons are then rapidly transported radially inward. This letter demonstrates, for the first time in detail, that geomagnetic storms are not necessary for causing dramatic enhancements in the outer radiation belt.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Diffusive transport of several hundred keV electrons in the Earth's slot region (2017)
    Wiley
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    Publication Date: 2017-10-01
    Description: We investigate the gradual diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward diffusion and decay of ~200-600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10-day non-disturbed period following the storm, the peak of electron fluxes gradually moved from L ~2.7 to L ~2.4, and the flux levels decreased by a factor of ~2-4 depending on the electron energy. We simulated the radial intrusion and decay of electrons using a 3-dimentional diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100-200 keV, the electrons experience fast transport across the slot region due to the dominance of radial diffusion; at energies of 200-600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of radial diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E 〉 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp ‘top-hat' shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between radial diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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