Lower hybrid resonance spherics

Summary

After a fractional-hop whistler, a trace of limited frequency range with somewhat higher dispersion, markedly growing when approaching the lower cutoff frequency, is frequently observed on spectrograms of broadband VLF measurements made by satellites moving in the outer ionosphere. This phenomenon, which we have called “LHR spheric”, has been studied on VLF measurements made by the Interkosmos-14 satellite in the height range of 500–1700 km. The results show that LHR spherics are created by the same mechanism as LHR whistlers that sometimes appear after ducted whistlers. In this event, it is a part of the electromagnetic energy radiated by a lightning flash which, on passing trough the ionosphere, has been transformed to quasi-electrostatic resonance waves. They reach the satellite in the same way as whistler-mode waves. Transformation of a part of the energy radiated by a lightning flash to electrostatic quasi-resonance waves is possible in the ionosphere due to the scattering of the original whistler wave on small-scale turbulence.