Abstract:
:Early observations 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 studies 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 boundary, with the inner edge of the outer radiation zone corresponding to the minimum plasmapause location. Recent observations have revealed unexpected radiation belt morphology, especially at ultrarelativistic kinetic energies (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 data 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.
journal_name
Naturejournal_title
Natureauthors
Baker 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 LJdoi
10.1038/nature13956subject
Has Abstractpub_date
2014-11-27 00:00:00pages
531-4issue
7528eissn
0028-0836issn
1476-4687pii
nature13956journal_volume
515pub_type
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