  Two mechanisms of anomalous attenuation of probe waves in the experiments of
ionosphere modification are discussed in the paper. The first mechanism is the
well-known conversion of ordinary wave into plasma waves due to scattering from
random irregularities in the upper-hybrid resonance region. The second
mechanism is the multiple scattering. This mechanism is responsible for
anomalous attenuation of extraordinary wave have been observed in several
experiments. Investigation of joint effect of both mechanisms gives additional
possibilities for diagnostics of artificial irregularities.

Plasma Physics