Short-period variations of ionospheric drifts at Collm and their connection with the dynamics of the lower and middle atmosphere

Studies of the intensity of horizontal drift velocity perturbations with pe riods 0.7 - 3 hours at the altitudes 80 - 110 km are made from the data of regular low-frequency D1 ionospheric reflection observations at Collm, Germ any (52 degreesN, 15 degreesE) in 1983 - 1999. Seasonal changes of variance s of short-period perturbations of zonal velocity reveal the main maximum i n summer and a smaller maximum in winter near the altitude 80 km and the tw o maxima at equinoxes near and above 100 km. Perturbation variances had the minima in 1985 -- 1987 and in 1996 -- 1998. Numerical modeling shows that IGWs generated in the strato-mesospheric jet stream may have substantial am plitudes at altitudes near and above 100 km and may modify seasonal variati ons of tropospheric IGWs. (C) 2001 Elsevier Science Ltd. All rights reserve d.