On the solar cycle dependence of winds and planetary waves as seen from mid-latitude D1 LF mesopause region wind measurements*

At the Collm Observatory of the University of Leipzig LF D1 low-frequency total re ̄ection nighttime wind measurements have been carried out continuously for more than two decades. Using a multiple regression analysis to derive prevailing winds, tides and the quasi-2-day wave from the half-hourly mean values of the horizontal wind components, monthly mean values of mesopause wind parameters are obtained that can be analysed with respect to long-term trends and in ̄uences of solar variability. The response of the prevailing wind to the 11-year solar cycle di€ers throughout the year. While in winter no signi®cant correlation between the zonal prevailing wind and solar activity is found, in spring and summer a negative correlation between the TWC can be seen from the measurements. This is connected with stronger vertical gradients of the zonal prevailing wind during solar maximum than during solar minimum. Since the amplitude of the quasi-2-day wave is dependent on the zonal mean wind vertical gradient, this is connected with a positive correlation between solar activity and quasitwo-day wave activity.