Observations of HF signals propagated over high latitude paths

A frequency agile transmitter has been installed within the polar cap at Clyde River, NWT, Canada (70°N, 69°W). Five receiving and data logging systems have been deployed to provide four transauroral paths and one path contained entirely within the polar cap region. Results from two receiving sites at Leicester, UK, and Boston, USA, during a one-month experimental campaign undertaken from 16 January to 10 February 1989, are used to illustrate some of the influences of the auroral oval and mid-latitude trough on HF propagation. The trough controls the time at which signals with frequencies between 18 and 23 MHz are lost in the evening. The auroral oval can give rise to night-time propagation of signals on frequencies much higher than the usual night-time MUF