Phenomena in the High-Latitude F Region of the Ionosphere under the Effect of Powerful HF Radio Waves at Frequencies above the Critical One of the F 2 Layer

In this paper, we present the results of experimental studies of phenomena in the high-latitude upper ( F -region) ionosphere caused by the impact of high-power HF radio waves of ordinary (O-mode) polarization at heating frequencies f H that significantly exceed the critical frequency of the F 2 layer ( f H – fоF 2 = 0.9–1.1 MHz). The results are based on experimental data obtained at the EISCAT/Heating HF heating facility in Tromsø, northern Norway (69.6° N, 19.2° E). In the experiments, a high-power HF radio wave of the O-polarization range was emitted in the direction of the magnetic zenith with a maximum effective radiation power of 350–550 MW. It was found for the first time that under conditions when a powerful HF radio wave of the O-polarization was not reflected from the ionosphere, ducts of increased electron density Ne are formed, and small-scale artificial ionospheric inhomogeneities and narrow-band (within a ±1-kHz band relative to the heating frequency) artificial radio emission of the ionosphere that are recorded at a distance of ~1200 km from the heating facility are generated. The characteristics of small-scale artificial ionospheric irregularities and the spectral structure of artificial radio emission of the ionosphere with alternative O/X heating to the magnetic zenith at frequencies significantly exceeding the critical frequency of the F 2 layer are compared. It was established that, in general, their behavior has the same character, but the evolution of the development of the considered phenomena during O and X heating is different.