An impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts

TitleAn impenetrable barrier to ultrarelativistic electrons in the Van Allen radiation belts
Publication TypeJournal Article
Year of Publication2014
AuthorsBaker, DN, Jaynes, AN, Hoxie, VC, Thorne, RM, Foster, JC, Li, X, Fennell, JF, Wygant, JR, Kanekal, SG, Erickson, PJ, Kurth, W, Li, W, Ma, Q, Schiller, Q, Blum, L, Malaspina, DM, Gerrard, A, Lanzerotti, LJ
JournalNature
Volume515
Issue7528
Pagination531 - 534
Date Published11/2014
ISSN0028-0836
KeywordsMagnetospheric physics; ultrarelativistic electrons; Van Allen Belts; Van Allen Probes
AbstractEarly observations1, 2 indicated that the Earth’s Van Allen radiation belts could be separated into an inner zone dominated by high-energy protons and an outer zone dominated by high-energy electrons. Subsequent studies3, 4 showed that electrons of moderate energy (less than about one megaelectronvolt) often populate both zones, with a deep ‘slot’ region largely devoid of particles between them. There is a region of dense cold plasma around the Earth known as the plasmasphere, the outer boundary of which is called the plasmapause. The two-belt radiation structure was explained as arising from strong electron interactions with plasmaspheric hiss just inside the plasmapause boundary5, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location6. Recent observations have revealed unexpected radiation belt morphology7, 8, especially at ultrarelativistic kinetic energies9, 10 (more than five megaelectronvolts). Here we analyse an extended data set that reveals an exceedingly sharp inner boundary for the ultrarelativistic electrons. Additional, concurrently measured data11 reveal that this barrier to inward electron radial transport does not arise because of a physical boundary within the Earth’s intrinsic magnetic field, and that inward radial diffusion is unlikely to be inhibited by scattering by electromagnetic transmitter wave fields. Rather, we suggest that exceptionally slow natural inward radial diffusion combined with weak, but persistent, wave–particle pitch angle scattering deep inside the Earth’s plasmasphere can combine to create an almost impenetrable barrier through which the most energetic Van Allen belt electrons cannot migrate.
URLhttp://www.nature.com/doifinder/10.1038/nature13956
DOI10.1038/nature13956
Short TitleNature


Page Last Modified: August 11, 2015