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Van Allen Probes observations of unusually low frequency whistler mode waves observed in association with moderate magnetic storms: Statistical study
Author(s) -
Cattell C. A.,
Breneman A. W.,
Thaller S. A.,
Wygant J. R.,
Kletzing C. A.
Publication year - 2015
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 - 10.1002/2015gl065565
Subject(s) - chorus , van allen radiation belt , van allen probes , equator , physics , plasmasphere , geomagnetic storm , magnetosphere , geophysics , amplitude , poynting vector , very low frequency , atmospheric sciences , earth's magnetic field , computational physics , latitude , magnetic field , astronomy , nuclear physics , optics , plasma , art , literature , quantum mechanics
We show the first evidence for locally excited chorus at frequencies below 0.1 f ce (electron cyclotron frequency) in the outer radiation belt. A statistical study of chorus during geomagnetic storms observed by the Van Allen Probes found that frequencies are often dramatically lower than expected. The frequency at peak power suddenly stops tracking the equatorial 0.5 f ce and f / f ce decreases rapidly, often to frequencies well below 0.1 f ce (in situ and mapped to equator). These very low frequency waves are observed both when the satellites are close to the equatorial plane and at higher magnetic latitudes. Poynting flux is consistent with generation at the equator. Wave amplitudes can be up to 20 to 40 mV/m and 2 to 4 nT. We conclude that conditions during moderate to large storms can excite unusually low frequency chorus, which is resonant with more energetic electrons than typical chorus, with critical implications for understanding radiation belt evolution.