This paper concerns the interaction between small-scale artificial ionospheric inhomogeneities and large-scale natural MHD waves (geomagnetic pulsations). The inhomogeneities were produced at F region altitudes by powerful HF radiation from the Sura heating facility in Russia. Diagnostics were provided by resonant scattering of decametric radio waves emitted by several broadcast and dedicated transmitters. The scattered waves were received at the UTR-2 radio telescope in Ukraine with a multichannel coherent receiver equipped with highly directional phased antenna arrays. This instrument allowed us to investigate spatial and temporal variations in intensity and frequency of the signals scattered by the inhomogeneities with the scale size of l≃10 m. Previous investigations have shown the existence of quasi-sinusoidal variations in the signal frequency associated with the E¿B plasma drift due to the MHD wave. In this study, we investigate similar periodicities in the signal intensity, which in some cases were observed simultaneously with the frequency variations. However, unlike the frequency variations, the intensity oscillations appeared to be considerably nonuniform within the pumped region of the ionosphere with a horizontal scale size of L≃100 km. We discuss different explanations for the detected effect and suggest that its most probable cause is a transformation of the MHD wave energy into the energy of the inhomogeneities. ¿ 2000 American Geophysical Union