Detection on the Intercosmos-24 satellite of VLF and elf waves stimulated in the topside ionosphere by the heating facility Sura

Abstract

Results are presented of a satellite experiment on the detection of VLF and ELF waves excited by irradiation of the night ionosphere F region by the field of a nonmodulated powerful radio wave. The excited VLF and ELF waves have been detected at topside ionosphere altitudes h = 500–1000 km in the frequency bands 7.5 kHz < f < 15 kHz and 8 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 of the ionosphere. The region of wave occurrence has well-defined boundaries. This points to propagation (guiding) of the observed low frequency waves along geomagnetic field lines. Possible generation mechanisms for the low frequency emission observed are discussed. It is shown that longitudinal ELF waves may be excited at altitudes of the topside ionosphere by beams of suprathermal electrons resulting from the action of a high-power radio wave on the ionosphere. These waves have a small group velocity in the direction orthogonal to the magnetic field. Occurrence of ELF oscillations detected onboard of satellite may be caused also by satellite motion in spatially inhomogeneous electrostatic field, connected with artificial irregularities of plasma density and accelerated electron beams. Whistler waves in the VLF band may result from conversion of lower-hybrid oscillations excited in the reflection region of powerful radio wave 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.