Occurrence and impact of off-great circle deflections from the auroral oval during varying geomagnetic conditions

High frequency (HF) radio wave propagation is sensitive to spatial and temporal changes in the ionosphere caused by space weather. Horizontal gradients in ionospheric electron density can deflect radio waves to off-great circle paths, negatively impacting HF radio communications and over-the-horizon radar. One significant source of electron density enhancements at high latitudes is auroral precipitation. During geomagnetic storms, the precipitation of high-energy electrons into the auroral zone ionosphere can create strong horizontal electron density gradients at ~100 km altitude, which are capable of significantly altering radio propagation paths.

In this study, ray tracing simulations are performed through model ionospheres with simulated auroral electron precipitation generated with the Canadian Empirical High Arctic Ionosphere Model (E-CHAIM). The results of these simulations are used to map out expected azimuthal deflections for propagation from two sub-auroral transmission locations (Ottawa and Meanook, Canada) to locations across Northern Canada. It is shown that there is a wide range of deflections possible depending on the intended target location, the strength of geomagnetic activity, and the location of the transmitter relative to the auroral oval. Generally, for moderate geomagnetic activity during local night, radio transmissions directed northeast and northwest experience significant eastward and westward deflections, respectively. However, for very strong geomagnetic activity where the auroral oval expands southward to be overhead above the transmitter, no deflections occur.