Statistical study of nighttime medium-scale traveling ionospheric disturbances using midlatitude airglow images

[1] We have investigated statistical characteristics of the nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at two stations, Rikubetsu (43.5degreesN, 34.8degreesMLAT) and Shigaraki (34.9degreesN, 25.4degreesMLAT), in Japan for 1998-2000 near the solar maximum period. Most of the observed MSTIDs propagate southwestward in the images. The typical wavelength, velocity, period, and amplitude are 100-300 km, 50-100 m/s, 0.5-1.5 h, and 5-15%, respectively. Seasonal variations in these parameters are not clear. The occurrence rate has a major peak (50-60%) in summer that appears similar to2 months earlier at lower latitudes and a minor peak in winter. Similar occurrence characteristics are obtained from midlatitude spread-F signatures using multipoint ionosonde data in Japan, though the coincidence of the spread-F and the MSTIDs in airglow images is only 10-15%.