Long-term trends and year-to-year variability of mid-latitude mesosphere/lower thermosphere winds

Tendencies of mesosphere/lower thermosphere winds are investigated using updated multi-year ground-based data obtained at three mid-latitude stations located at Collm (Germany), Obninsk (Russia) and Saskatoon (Canada). For the first time for the mesosphere/lower thermosphere winds we consider in this study a family of trends, which includes both broken and straight-lines, to check a possible change of the wind tendencies during 1964–2004. General peculiarities of year-to-year wind variations are considered for annual mean, winter and summer prevailing winds and semidiurnal tides. Our results suppose a change in rates/directions of wind tendencies during the time interval 1964–2004. In particular, the annual mean zonal (eastward) wind decreases until the 1980s, but after that does not have a significant trend; similarly, the annual mean meridional (northward) wind increases until the 1990s and then does not have a significant trend. The behaviour of the summer prevailing wind both for the meridional and zonal components differ from that of annual winds, so that they increase after the trend's break. Rather large rates of decrease of tidal amplitudes (1.1–1.4 m/s/year) in the earlier years of measurements become smaller (about 6 times) in the beginning of the 1970s.