Interaction between artificial ionospheric irregularities and natural MHD waves

This paper concerns the interaction between small-scale artificial ionosphe ric inhomogeneities and large-scale natural MHD waves (geomagnetic pulsatio ns). The inhomogeneities were produced at F region altitudes by powerful HF radiation from the Sura heating facility ill Russia, Diagnostics were prov ided by resonant scattering of decametric radio waves emitted by several br oadcast and dedicated transmitters. The scattered waves were received at th e UTR-2 radio telescope in Ukraine with a multichannel coherent receiver eq uipped with highly directional phased antenna arrays, This instrument allow ed us to investigate spatial and temporal variations in intensity and frequ ency of the signals scattered by the inhomogeneities with the scale size of l similar to 1.0 m. Previous investigations have shown the existence of qu asi-sinusoidal variations in the signal frequency associated with the E x B plasma drift due to the MHD wave. In this study, we investigate similar pe riodicities in the signal intensity, which in some cases were observed simu ltaneously with the frequency variations. However, unlike the frequency var iations, the intensity oscillations appeared to be considerably nonuniform within the pumped region of the ionosphere with a horizontal scale size of L similar or equal to 100 km. We discuss different explanations for the det ected effect; and suggest that its most probable cause is a transformation of the MHD wave energy into the energy of the inhomogeneities.