HF RADAR OBSERVATIONS OF DECAYING ARTIFICIAL FIELD-ALIGNED IRREGULARITIES

Bistatic HF radar scatter from magnetic field-aligned irregularities c reated by the Sura heater near Nizhny Novgorod, Russia, has been detec ted and analyzed at the UTR 2 decametric radio telescope near Kharkov, Ukraine. The decay phase of the irregularities exhibits two decay tim e constants in general. The shorter time constant, which is only somet imes seen, is consistent with classical diffusive dissipation theory f or small-scale, field-aligned waves. The longer time constant, which i s almost always present, is much too long to be accounted for by diffu sion. It is more likely associated with the decay of large- and interm ediate-scale plasma turbulence. Three-wave nonlinear interaction with turbulent modes is shown to be capable of generating the field-aligned irregularities.