Appearance of VLF and ELF-noises in topside ionosphere under the action of high power radio wave from data of satellite intercosmos-24

Abstract

Results of a satellite experiment are presented on detection of VLF and ELF-waves excited by irradiation of the night ionosphere F-region by the field of a nonmodulated high-power radio wave. The excited VLF and ELF-waves have been detected at the topside ionosphere heights h=500–1000 km in the frequency bands 8 kHz<f<1.5 kHz and 10 Hz<f<1.5 kHz at distances less than 50–100 km from the centre of the magnetic force tube passing through the heated spot in the ionosphere. The region of wave appearance has well-defined boundaries. This points to propagation (guiding) of the observed low frequency waves along geomagnetic field lines. Possible mechanisms of observed low frequency emission generation are discussed. It is shown that longitudinal ELF-waves may be excited at the heights of topside ionosphere by beams of suprathermal electrons resulting from the action of high-power radio wave on the ionosphere. These waves have a small group velocity in the direction orthogonal to the magnetic field. Whistler waves in the VLF-band may result from conversion of lower-hybrid oscillations excited by the high-power wave into the whistler mode due to scattering by artificial small-scale field-aligned irregularities. The whistlers generated can propagate to the satellite along artificial ducts formed within the disturbed magnetic force tube.