LARGE HF BEARING ERRORS FOR PROPAGATION PATHS CONTAINED WITHIN THE POLAR-CAP

Large electron-density gradients in the polar-cap ionosphere, associat ed with the convection of patches of overdense plasma and the presence of high-latitude auroral arcs, produce tilted reflecting surfaces whi ch result in HF signals propagating over paths well displaced from the great circle. Measurements have been made at a very high-latitude rec eiving site of signals propagated over paths contained within the pola r cap. Systematic swings in the bearing of the received signal of up t o +/-100 degrees from the great circle path were recorded and their ch aracteristics related to the directional components of the interplanet ary magnetic field and the level of geomagnetic activity, as these geo magnetic parameters play an important role in determining the state of the high-latitude ionosphere.