Ionospheric observations of F region artificial plasma turbulence, modified by powerful X-mode radio waves

We study the influence of additional X-mode heating of the ionospheric plasma on the features of artificial ionospheric turbulence, induced in the ionospheric F region by O-mode waves over the 'Sura' heating facility (Nizhny Novgorod, Russia). The X heating is shown to suppress the generation of HF plasma turbulence resulting from the development of both the parametric decay and thermal parametric instabilities. Typical times of variations in the turbulence intensity change from not more than 0.1 s to approximately 10 s, strongly depending on the heating scheme. Aftereffects of the X heating last up to 30-60 s. We distinguish at least three types of phenomena, according to the observed typical times of the processes, and discuss possible reasons for each of them. (Author)