Attenuation of scintillation of discrete cosmic sources in the case of non-resonance HF heating of the upper ionosphere

As is known [1], imaging HF riometers represent receiving radio systems consisting of a multi-beam phased array and output radiometer. Systems of the kind are intended for monitoring space-and-time distribution of cosmic radio noise absorption in the lower ionosphere. Today there is a chain of such instruments over the world. Most of these operate at 38.2 MHz. In our earlier studies [2-5] we used these facilities to investigate inhomogeneous structure of the ionospheric F-region by the scintillation technique. Four most powerful discrete cosmic HF sources in the Northern sky, namely, Cassiopeia A, Cygnus A, Taurus A and Virgin A, have been selected as sources of the probe signal.