Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating smallscale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GWspectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.

We analyse 43 years of mesosphere/lower thermosphere (MLT) horizontal winds obtained from a joint analysis of low frequency (LF) spaced receiver lower ionospheric drift measurements from 1979 through 2006 and very high frequency (VHF) meteor radar wind observations since 2004 at Collm (51°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 activity as well as LF reflections in the MLT. In the 1980s and 1990s, 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 also analyse interannual variability, in particular with respect to a possible signature of NAO and ENSO. These signals, however, are relatively weak and not stable throughout the time of observations. / Wir analysieren 43 Jahre Messungen horizontaler Winde in der Mesosphäre/unteren Thermosphäre (MLT) über Collm (51°N, 13°E), die aus einer gemeinsamen Analyse von Langwellen (LF) -Driftmessungen in der unteren Ionosphäre von 1979 bis 2006 und VHF-Meteorradar-Windbeobachtungen seit 2004 gewonnen wurden. Aufgrund der Einschränkungen der früheren LF-Messungen beschränken wir uns auf die Analyse der mittleren monatlichen Windgeschwindigkeiten bei 90 km, welches die Höhe maximaler Meteorraten sowie die mittleren nächtlichen LF-Reflexionshöhen in der MLT darstellt. In den 1980er und 1990er Jahren beobachten wir das ganze Jahr über hauptsächlich positive Trends des zonalen mittleren Windes, während die Stärke des meridionalen Windes sowohl im Sommer als auch im Winter tendenziell abnimmt. Wir analysieren auch die Variabilität von Jahr zu Jahr, insbesondere im Hinblick auf eine mögliche Signatur von NAO und ENSO. Diese Signale sind jedoch relativ schwach und nicht über die gesamte Beobachtungszeit stabil nachweisbar.

Implementing a nonlinear gravity wave (GW) parameterization into a mechanistic middle and upper atmosphere model, which extends to the lower thermosphere (160 km), we study the response of the atmosphere in terms of the circulation patterns, temperature distribution, and migrating terdiurnal solar tide activity to the upward propagating small scale internal GWs originating in the lower atmosphere. We perform three test simulations for the Northern Hemisphere winter conditions in order to assess the effects of variations in the initial GW spectrum on the climatology and tidal patterns of the mesosphere and lower thermosphere. We find that the overall strength of the source level momentum flux has a relatively small impact on the zonal mean climatology. The tails of the GW source level spectrum, however, are crucial for the lower thermosphere climatology. With respect to the terdiurnal tide, we find a strong dependence of tidal amplitude on the induced GW drag, generally being larger when GW drag is increased.