Dependence of Characteristics of SURA Induced Artificial ULF/VLF Signals on Geomagnetic Activity

Abstract

A comprehensive study of artificial ionospheric signal generation in the ULF/VLF bands at SURA facility in Russia was conducted during the past 4 years. We investigated the influence of geomagnetic activity on the characteristics of artificial low-frequency signals under the background of increasing solar activity. No correlation of artificial ULF signals with variations of Earth’s magnetic field was observed for weak geomagnetic disturbances \((Kp \le 3)\) while the VLF signals increased in the growth phase of the geomagnetic perturbation. In case of strong magnetic storm \((Kp \ge 5+)\) a tendency of the amplitude of the ULF/VLF signals decrease with increasing magnetic disturbance was observed. Sometimes, the modulation of artificial ULF signals with a period of 15–30 s was detected in the decay phase of magnetic storms. During storm time, a change in the polarization of artificial VLF emissions was detected. The right polarization becomes predominant. Interpretation of observed peculiarities of artificial VLF signals is given in the context of the physical mechanism of ionospheric current drive by RF pumping.