Radiation belt electron precipitation due to VLF transmitters: Satellite observations

Abstract

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. Copyright 2008 by the American Geophysical Union.