Anomalous absorption effects produced by high power radio waves in the high latitude ionosphere

High power HF radio waves can produce plasma instabilities in the ionosphere which induce major changes in the propagation characteristics of other HF signal propagating through the disturbed region. Experiments to investigate some of these disturbance effects were undertaken using the Max Planck Institut fur Aeronomie, Lindau heating facility at Tromso, Norway. Particular attention is given to the anomalous absorption effects discovered and to the induced phase changes observed in the diagnostic signals. The observations are interpreted in terms of the plasma instabilities generated and are of interest in assessing the performance of HF communication systems when disturbances of this nature are produced in the ionosphere.