IONOSPHERIC HEATING BY VLF TRANSMITTERS

A series of experiments was carried out in 1983-1985 to investigate precipitation of radiation belt electrons by Omega Australia onto the great circle path from the 22.3 kHz NWC transmitter (North West Cape, Australia) to Dunedin, New Zealand. These were similar in concept to the experiment described by INAN [(1990), Geophys. Res. Lett. 17, 729] using the NAU transmitter to induce electron precipitation onto the great circle path from the 24.0 kHz NAA transmitter (Maine) to Palmer Station (PA), Antarctica. Unlike the perturbations received by Inan which indicated only heating effects by the NAU transmitter, our observations showed both a delayed modulation expected of electron precipitation effects and the prompt modulation expected of heating effects. However, we were able to duplicate (and explain) the prompt modulation effect using a local signal generated in our laboratory which thereby throws doubt on the validity of this effect in both experiments.