Summer mesospheric observations using the MU radar at Shigaraki, Japan show that radar echoes could be detected before sunrise under some circumstances. The pre-sunrise radar echoes observed at heights above 80 km are weak but clearly occur in a layer. Strong radar echoes observed after sunrise at similar heights show an unusual broadening of the spectral width in the echo power. This indicates the presence of strong atmospheric turbulence. In addition, frequency spectra for the vertical wind fluctuations show an enhancement of the spectral power density in a wide range of periods shorter than the local Brunt-V¿is¿l¿ one. This is consistent with the occurrence of strong turbulence layer in the upper mesosphere though not immediately identified with the turbulence activity. Thus the presence of strong turbulence layer might yield us a possibility of detecting radar echoes before sunrise. ¿ 1998 American Geophysical Union