MIDDLE AND UPPER-ATMOSPHERE RADAR OBSERVATIONS OF THE DISPERSION-RELATION FOR IONOSPHERIC GRAVITY-WAVES

By observing the ionospheric F region simultaneously in multiple beams with the middle and upper atmosphere radar, we have been able to trac k the passage of gravity waves and measure their propagation character istics. Here we investigate the dispersion relation for these waves. T his relation varies widely from day to day, even on two successive mag netically extremely quiet days. On average, however, we find that the wave horizontal phase trace speed is about 200 m/s for periods from 60 to 130 min with little variation with solar or magnetic activity. The re is some indication that the speed increases slightly from equinox t o winter.