Observations of VLF transmitter‐induced depletions of inner zone electrons

Abstract

Precipitation spikes of electrons, in which the energy spread of the peak is narrow (less than 50 keV) and the peak energy is a strong function of the location in L, have been observed in the region 1.5 < L < 2.0 and have been ascribed to interactions between waves from high power VLF transmitters on the ground and the precipitated electrons [Vampola and Kuck, 1978; Imhof et al., 1981]. On numerous occasions when these spikes were observed at low altitude by instrumentation on the S3‐2 satellite, a significant depletion of electrons at the same energies was observed high on the field line. These depletions indicate that the loss rate of electrons due to VLF transmitters is significant and usually exceeds the rate at which radial diffusion is refilling those field lines. Electrons with energies between 36 keV and 317 keV in the region 1.9 < L < 1.6 were observed to have lifetimes limited to a few days by interactions with waves from VLF transmitters. Thus the outer edge of the inner zone is defined by this wave‐particle process.