Observations of the direction of arrival of HF signals propagated over high latitude and mid latitude paths

Direction of arrival measurements have been made at two locations in Canada. One is a mid-latitude site observing an East-West path approximately tangential to the auroral oval. The other is a very high latitude site close to the geomagnetic pole at which signals propagating over two paths, one short path contained entirely within the polar cap and a second trans-auroral oval path on a similar true bearing were observed. Measurements at the mid-latitude site indicated that large bearing errors of up to about -90° are observed during periods of enhanced geomagnetic activity. When large northerly bearing errors are observed at the mid-latitude site, large bearing errors are observed at the high latitude site for signals reflected from the polar cap ionosphere. A feature of these high latitude measurements is a large (±50°) quasi-periodic swing in the direction of arrival. These are attributed to reflection from patches of over-dense plasma