DEMETER observations of ionospheric heating by powerful VLF transmitters

Abstract

We report DEMETER spacecraft observations of ionospheric heating produced above powerful VLF transmitters by their intense radiated electromagnetic (EM) signals. We compare the heating effects of signals from the 1 MW NWC transmitter in Australia with those produced by signals from the 885 kW NAA transmitter in Maine. Significant observable effects include perturbations in plasma density and thermal electron temperature, and the production of quasi-electrostatic (QE) VLF plasma wave bands, both over the transmitters, and, in the case of NWC, also in the magnetically conjugate region. In the regions in which the QE wave bands were observed, they were invariably accompanied by a band of ELF turbulence with maximum intensity below 300 Hz. Such turbulence has in the past been associated with the presence of small scale plasma density irregularities. This association suggests that heating effects due to NWC are far-reaching and extend along B(o) into the conjugate hemisphere where they are expressed in part as small scale plasma density fluctuations.