Climatology of the 8-hour tide over Collm (51.3°N, 13°E)

The horizontal winds in the mesosphere and lower thermosphere (MLT) at heights of about 80-100 km have been measured by the SKiYMET meteor radar at Collm, Germany (51.3°N, 13°E). The radar has been operating continuously since July 2004, and the data from December 2004 – December 2009 were used for constructing a climatology of the 8-h tide. The 8-h tide appears to be a regular feature in the MLT. In particular, the amplitude shows a clear seasonal behaviour, with maximum values around the equinoxes, and generally an increase with height. The largest amplitudes occur in autumn, sometimes reaching values above 15 m/s, but they are significantly smaller during summer (~1 m/s). The phase is early in winter and advances to later times in summer. In general, the phase difference between the zonal and meridional components is close to +2 h. The vertical wavelengths are short in summer (~30 km) but significant longer during the rest of the year. The results were compared with observations from locations of different latitudes