Oblique propagation of HF signals in the polar cap ionosphere

Observations of the effect of polar patches (fast moving regions of strong ionization) on the Doppler and time of flight behavior of HF signals propagating in the polar cap ionosphere are presented. The observed patch-induced characteristics of the HF propagation have successfully been reproduced using a simple model of the movement of the patches, thereby allowing the trajectory and velocity of a patch to be estimated. The increased ionization in the patch allows higher frequencies to reflect than those that would normally be expected. A comparison of the fluctuations in the measured TEC data (a proxy for the presence of patches) with the detection of HF signals has provided some evidence for this relationship.