Properties of the ULF/VLF Signals Generated by the Sura Facility in the Upper Ionosphere

The results of studying the generation of low-frequency radiation in the ionosphere affected by high-power modulated HF radiation of the Sura facility are presented. A large amount of data on characteristics of the ULF/VLF artificial signals observed in the night time, which indicate the manifestation of a new generation mechanism not related to the quasistationary ionospheric current modulation effect, have been obtained for the first time at the mid-latitudes. The results of studying the dependence of the signal value on the beam inclination of the pump wave and the distance to the observation point from the facility are presented. It is shown that the signals can be both right- and left-hand polarized depending on the level of geomagnetic activity. The measured time delay of the ULF signal indicates the location of the source at the F-layer maximum. Interpretation of the observed characteristics of artificial low-frequency signals based on a ponderomotive excitation mechanism of the diamagnetic ring current around the HF radiation beam at a modulation frequency agrees with the main results of the experiment.