Observations of Doppler spread, time-of-flight and direction of arrival of HF radio signals on a path affected by the mid-latitude trough

Measurements of the time-of-flight and direction of arrival are presented for an HF radio signal on a subauroral path between Sweden and the UK. During the day, the signal usually arrives from the great circle path (GCP) direction. However, at night, especially during winter and equinoctial months, the signal often arrives at azimuths displaced from GCP. To the north, signals are probably scattered from irregularities in the trough wall.