Long-term variability of mid-latitude mesosphere-lower thermosphere winds over Collm (51°N, 13°E)

Radar observations of mesosphere/lower thermosphere (MLT) winds at middle latitudes obtained from meteor radar 2004-date and the low-frequency drift method 1979-2008 have been combined to obtain a homogeneous long-term data set of MLT dynamics at 90 km altitude. The data are analyzed to obtain tendencies of prevailing winds during the last three decades. On a seasonal time scale, the zonal winds show positive trends towards more westerly winds throughout the year, while the meridional wind trends are negative in autumn/winter and positive in spring/summer. There is a tendency that the trends of both zonal and meridional summer prevailing winds are changing after 1995. Using a numerical circulation model with realistic ozone and carbon dioxide fields and with tropospheric/lower stratospheric circulation taken from ERA reanalyses, the observed trend changes can be reproduced qualitatively. The MLT wind trends are, according to the model, mainly due to the influence of changes in tropospheric and lower stratospheric dynamics.