Comparative study of interannual changes of the mean winds and gravity wave activity in the middle atmosphere over Japan, Central Europe and Canada

Abstract

Results are presented of measurements of the mean wind and its variances attributed to the intensity of internal gravity waves (IGWs) with the MU radar at Shigaraki, Japan, from 1986 to 1999, with the low-frequency ionospheric drift method Dl at Collm, Germany and with the medium frequency (MF) radar at Saskatoon, Canada, between 1983 and 1999 at altitudes 65–80, 80–110 and 60– 100 km , respectively. The amplitudes of eastward–westward seasonal variations of the mean zonal wind in the mesosphere and lower thermosphere are different in different years. The mean wind and IGW intensities show substantial seasonal, quasi-biennial and interannual variations, which may be different at different altitudes. The measurements show differences in the interannual changes, IGW intensities at different locations. Comparison of interannual changes of the wind and drift velocity variances reveal substantial differences between Saskatoon and Collm and Shigaraki. Such differences in seasonal and interannual changes in the wind perturbation variances may be attributed to the changes in the strengths of IGW sources in the atmosphere at different altitudes and locations and with the conditions of wave propagation in the lower, middle and upper atmosphere. Among the possible reasons for these changes could be solar activity, the eruption of the Pinatubo volcano in June 1991 and, probably, interannual changes of the temperature of oceans in tropics (El Ninö events) on the circulation of the middle and upper atmosphere.