Characterization of Artificial, Small-Scale, Ionospheric Irregularities in the High-Latitude F Region Induced by High-Power, High-Frequency Radio Waves of Extraordinary Polarization

Abstract

The results of experimental studies of characteristics of artificial, small-scale, ionospheric irregularities in the high-latitude ionospheric F region caused by the controlled injection of high-power, high-frequency (HF) radio waves of extraordinary polarization (X mode) are presented. The experiments were carried out at the HF European Scientific Association (EISCAT)/Heating complex (Tromsø, northern Norway (69.6° N, 19.2° E)) in a wide range of heating frequencies (4–8 MHz) with an effective radiation power of 100 to 700 MW. It is shown that the generation of irregularities upon X heating occurs in the regular F region of the ionosphere under quiet magnetic conditions at heating frequencies both lower and higher than the critical frequency of the F2 layer. The rise and relaxation times of the irregularities, as well as the threshold powers of their excitation are determined. It is ascertained that the characteristics of irregularities upon X heating strongly depend on the heating frequency, the relationship between the heating frequency and the critical frequency of the F2 layer, and the conditions preceding the start of the heating cycle (“cold” start in the first X-heating cycle or subsequent X-heating cycles). The characteristics of irregularities upon exposure of the high-latitude ionospheric F region to high-power long radio waves of extraordinary (X mode) and ordinary (O mode) polarization are compared.