Gravity wave momentum fluxes in the MLT-Part I: Seasonal variation at Collm (51.3°N, 13.0°E)

By using a method presented by Hocking (2005), wind variances and gravity wave momentum fluxes in the mesosphere and lower thermosphere have been derived from all-sky interferometric meteor radar wind measurements at Collm, Germany (51.3°N, 13.0°E), during 2004 through 2009. We present vertical profiles of long-term mean monthly mean variances and momentum fluxes. Gravity wave variances show a semi-annual oscillation around 90 km altitude, and generally increase with height. An exception are the summer months where the maximum is measured around 88 km and amplitudes are decreasing above that height. A comparison of momentum fluxes and mean background winds emphasizes the coupling between gravity waves and the background circulation. 3-monthly means of wind and wind variance for individual seasons show stronger interannual variability in winter than in summer, and an indication for mesosphere wind filtering of gravity waves being responsible for this variability.