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An empirically observed pitch‐angle diffusion eigenmode in the Earth's electron belt near L * = 5.0
Author(s) -
O'Brien T. P.,
Claudepierre S. G.,
Blake J. B.,
Fennell J. F.,
Clemmons J. H.,
Roeder J. L.,
Spence H. E.,
Reeves G. D.,
Baker D. N.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2013gl058713
Subject(s) - physics , hiss , pitch angle , diffusion , exponential decay , electron , normal mode , exponential function , flux (metallurgy) , van allen radiation belt , scattering , computational physics , atomic physics , magnetosphere , optics , nuclear physics , plasma , quantum mechanics , mathematical analysis , geophysics , chemistry , mathematics , organic chemistry , vibration
Using data from NASA's Van Allen Probes, we have identified a synchronized exponential decay of electron flux in the outer zone, near L * = 5.0. Exponential decays strongly indicate the presence of a pure eigenmode of a diffusion operator acting in the synchronized dimension(s). The decay has a time scale of about 4 days with no dependence on pitch angle. While flux at nearby energies and L * is also decaying exponentially, the decay time varies in those dimensions. This suggests the primary decay mechanism is elastic pitch angle scattering, which itself depends on energy and L * . We invert the shape of the observed eigenmode to obtain an approximate shape of the pitch angle diffusion coefficient and show excellent agreement with diffusion by plasmaspheric hiss. Our results suggest that empirically derived eigenmodes provide a powerful diagnostic of the dynamic processes behind exponential decays.