Wide band attenuation of radio waves caused by powerful HF waves: Saturation and dependence on ionospheric variability

The phenomenon of wide band attenuation, i.e., anomalous absorption of an HF wave in the F region subjected to modification by a powerful HF wave, has been measured using the Tromsø heating facility. Two types of results were found. In a quiet F region situation, the attenuation amounted to approximately 15 dB and did not change when the effective radiated heating power was lowered from 160 to 20 MW. In a variable F region, indicated by a high fading rate of the diagnostic wave, the absorption was considerably less than 15 dB and showed a strong dependence on the heating power. An explanation for both types of results is offered by extending a recent theory of Das and Fejer.