We have regular monitored mesospheric winds at 60--85 km for three years with the MU radar (35 ¿N, 136 ¿E), and have found that the variance of wind velocity fluctuations for periods from 5 min to 2 hr shows a semi-annual variation with a significant peak in summer centered in July and irregular enhancements in winter. The zonal momentum flux induced by gravity waves shows eastward and westward maxima in July--August and December--February, respectively. Typical eastward accelerations at the 70 km altitude range from 7 to 13 m/s/day and from -8 to -11 m/s/day in summer and winter, respectively, which agree fairly well with theoretical predictions. ¿ American Geophysical Union 1990