Radiation belt electron precipitation due to VLF transmitters: Satellite observations
Résumé
In the Earth’s inner magnetosphere, the distribution of
energetic electrons is controlled by pitch-angle scattering by
waves. A category of Whistler waves originates from
powerful ground-based VLF transmitter signals in the
frequency range 10–25 kHz. These transmissions are
observed in space as waves of very narrow bandwidth.
Here we examine the significance of the VLF transmitter
NWC on the inner radiation belt using DEMETER satellite
global observations at low altitudes. We find that
enhancements in the 100–600 keV drift-loss cone
electron fluxes at L values between 1.4 and 1.7 are linked
to NWC operation and to ionospheric absorption. Waves
and particles interact in the vicinity of the magnetic
equatorial plane. Using Demeter passes across the drifting
cloud of electrons caused by the transmitter; we find that
300 times more 200 keV electrons are driven into the
drift-loss cone during NWC transmission periods than
during non-transmission periods. The correlation between
the flux of resonant electrons and the Dst index shows that
the electron source intensity is controlled by magnetic storm
activity.
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