Features of spread-F at Grand Bahama, a temperate latitude station

The spread-F echoes on the vertical incidence ionograms at a temperate latitude station outside the equatorial F-region anomaly belt are shown to start with additional p'-f traces near the penetration frequencies due to off-vertical echoes. With time, these additional p'-f traces increase in intensity and in number, and extend to lower frequencies giving rise to range type of spread-F. The temperate latitude spread-F is suggested to arise mostly from the reflection of radio waves from the ripples and undulations in the iso-ionic surfaces in the ionosphere rather than from the scattering of radio waves from plasma instabilities. These characteristics are thus very different from the development of spread-F at equatorial stations