Evolution and slow decay of an unusual narrow ring of relativistic electrons near L ~ 3.2 following the September 2012 magnetic storm

• Published in: Geophysical research letters Vol. 40; no. 14; pp. 3507 - 3511
• Main Authors: Thorne, R. M., Li, W., Ni, B., Ma, Q., Bortnik, J., Baker, D. N., Spence, H. E., Reeves, G. D., Henderson, M. G., Kletzing, C. A., Kurth, W. S., Hospodarsky, G. B., Turner, D., Angelopoulos, V.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 28.07.2013; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Decay; Decay rate; Earth sciences; Earth, ocean, space; Electrons; Exact sciences and technology; Hiss; Magnetic storms; Outer radiation belt; Particle accelerators; Pitch angle; Plasmasphere; plasmaspheric hiss; Relativism; relativistic electrons; Scattering; Storms; Narrows; New York; United States; depletion; time scales; magnetic storms; Pitch angle; Relativistic electron; North America; Long term; duration; dynamics; instruments; Outer radiation belt; migration; protons; Plasmapause; quantitative analysis; stability; energy
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/grl.50627

A quantitative analysis is performed on the decay of an unusual ring of relativistic electrons between 3 and 3.5 RE, which was observed by the Relativistic Electron Proton Telescope instrument on the Van Allen probes. The ring formed on 3 September 2012 during the main phase of a magnetic storm due to the partial depletion of the outer radiation belt for L > 3.5, and this remnant belt of relativistic electrons persisted at energies above 2 MeV, exhibiting only slow decay, until it was finally destroyed during another magnetic storm on 1 October. This long‐term stability of the relativistic electron ring was associated with the rapid outward migration and maintenance of the plasmapause to distances greater than L = 4. The remnant ring was thus immune from the dynamic process, which caused rapid rebuilding of the outer radiation belt at L > 4, and was only subject to slow decay due to pitch angle scattering by plasmaspheric hiss on timescales exceeding 10–20 days for electron energies above 3 MeV. At lower energies, the decay is much more rapid, consistent with the absence of a long‐duration electron ring at energies below 2 MeV. Key Points Relativistic electrons injected into the plasmasphere have long lifetimes The loss rate is controlled by scattering by whistler‐mode hiss Isolated rings of relativistic electrons form during magnetic storms