Van Allen Probes observations of unusually low frequency whistler mode waves observed in association with moderate magnetic storms: Statistical study.
We show the first evidence for locally excited chorus at frequencies below 0.1fce(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 0.5fceandf/fcedecreases rapidly, often to frequencies well below 0.1fce(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.
School of Physics and Astronomy University of Minnesota, Twin Cities Minneapolis Minnesota USA.
C A
CA
Cattell
School of Physics and Astronomy University of Minnesota, Twin Cities Minneapolis Minnesota USA.
A W
AW
Breneman
School of Physics and Astronomy University of Minnesota, Twin Cities Minneapolis Minnesota USA.
S A
SA
Thaller
School of Physics and Astronomy University of Minnesota, Twin Cities Minneapolis Minnesota USA.
J R
JR
Wygant
Department of Physics and Astronomy University of Iowa Iowa City Iowa USA.
C A
CA
Kletzing
Department of Physics and Astronomy University of Iowa Iowa City Iowa USA.
W S
WS
Kurth
chorus; outer radiation belt
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