The temperature measurements taken at Kühlungsborn (54°N, 12°E) with two different lidars yield data sets covering the whole altitude range between the troposphere and the lower thermosphere (1-105 km). Measurements from more than 230 nights were collected (2002-2006). Apart from some gaps due to adverse weather conditions in winter, the measurements were well distributed throughout the year. Comprehensive information on the seasonal variation of temperatures and of the gravity wave activity was extracted from this data set.
The seasonal variation of lidar temperatures matches other data sets, as well. The largest differences occur in winter because of stratospheric warmings accompanied by mesospheric cooling. The results of a harmonic fit represent the original data very well without greater inhomogeneities. In the analyses of gravity wave activity the dominating vertical wavelengths do not show any seasonal variation. In contrast to this, the temperature fluctuations experience a clear annual cycle with a maximum in winter. The most significant winter-summer difference exists at about 60 km where the temperature fluctuations in winter are more than twice as large as they are in summer. Further investigations have shown that, apart from the different wave filtering by winds, the density and temperature background and the wave damping also play an important role in creating the seasonal variation of gravity wave activity.
The superposition of the waves and the significance of background variables were investigated by means of a linear gravity wave simulation. It was found that only few wave modes dominate the wave structures, but these structures are generated by some hundred waves. The importance of the background (density, temperature, wind) concerning the winter-summer ratio of temperature fluctuations and the wave propagation were confirmed by the simulation. Here however, the source plays a minor role for this ratio.