MU radar-RASS observations were conducted on July 28--31, 1994 at Shigaraki, Japan (35 ¿N, 136 ¿E), to determine the detailed time variations of all three wind components and virtual temperature in the lower troposphere. We discuss their frequency spectra in comparison with a theoretical model of gravity waves. Assuming hydrostatic equilibrium, we also estimated the vertical wind velocity from the time derivative of temperature variations at each altitude. We found that the frequency spectra of the derived vertical wind were more consistent with a gravity wave model than those spectra calculated from direct measurements of the vertical wind. ¿ American Geophysical Union 1996