Long-term changes of midlatitude horizontal mesosphere/lower thermosphere winds over four decades

We analyse 42 years of mesosphere/lower thermosphere (MLT) horizontal winds obtained from a joint analysis of LF D1 lower ionospheric drift measurements from 1979 through 2006 and VHF meteor radar wind observations since 2004 at Collm (52°N, 13°E). Due to limitations of the earlier LF measurements, we restrict ourselves to the analysis of monthly mean winds near 90 km, which represents the height of maximum meteor heights as well as LF reflections in the MLT. We observe mainly positive trends of the zonal prevailing wind throughout the year, while the meridional winds tend to decrease in magnitude in both summer and winter. We compare these results with long-term MF partial reflection radar observations at 81–85 km over Juliusruh (55°N, 13°E) since 1990, and find general qualitative agreement of trends except for summer. The latter can be explained by the different altitudes considered, and by the latitudinal change of the summer mesospheric jet.