Clear-air echoes were observed in Nagoya with two radars of 3.2cm in wavelength. Most of echoes were dot echoes. The target of dot echoes are inferred to be insects on the basis of their backscattering cross sections and the time variation of received signals of each echo. Diurnal variations of the number of dot echoes were carefully studied. And it was suggested that the number and spatial distribution of dot echoes have close relation to growth and break down of the mixing layer. Horizontal speeds of dot echoes were also examined, and they were not always indicating wind speeds in light wind condition.
There also appeared another type of clear-air echoes which seemed to be attributed to refractive index fluctuations in the atmosphere. They were observed as wavelike echoes associated with internal gravity waves. The value of Cn2 estimated on the basis of the intensity of the echoes would be as high as 10-12cm-2/3. This value implies the possibility of the existence of intense turbulence in stable stratification which can be detected even by the radar of 3.2cm in wavelength.