During the summers of 1992 and 1994, experiments were conducted in Germany (52 ¿N) to investigate the region of the summer mesopause in connection with mesospheric summer echoes (MSE). MSE form in layers and are associated with dramatically enhanced radar scattering cross sections. Furthermore, since the summer mesopause is characterized by very low temperatures, it has been proposed that MSE layers are related to the presence of subvisible ice particles. Parallel measurements were made using the Sounding System (SOUSY) VHF radar and Rayleigh lidar. Radar observations showing MSE signatures are presented together with accompanying temperature profiles obtained from the lidar data. Generally, the ambient temperatures in the summer mesosphere at midlatitudes are above that required to create ice crystals. However, the presence of waves can reduce the temperature. Our observations show this to be the case. In particular, during one of the MSE events, two long-period inertia gravity waves were observed. These waves had estimated local periods of 6 and 8 hours with accompanying vertical wavelengths of 10 and 15 km, respectively. We find a good correlation between the locations of the calculated temperature minima and the observed MSE layers. Furthermore, the temperature minima were generally below the saturation temperature for water vapor, lending support to the supposition that the backscatter is connected with the presence of ice particles. ¿ 1997 American Geophysical Union