Peculiarities of interannual changes in the mean wind and gravity wave characteristics in the mesosphere over Shigaraki, Japan

Results are presented of month by month measurements of the mean wind and i ntensity and momentum fluxes of internal gravity waves (IGWs) with the Midd le and Upper atmosphere radar (MU radar) at the altitudes 65 - 80 km at Shi garaki, Japan (35 degrees N: 136 degrees E) in 1986 - 1997. The mean zonal wind is east ward in winter and westward in summer, but the amplitude of th ese annual variations is different in different years, having a minimum in 1992 - 1994. The mean meridional wind shows substantial quasi-bi-annual var iations. IGW intensities and momentum fluxes had a maximum in 1991 - 1994. Some possible reasons for such interannual changes are discussed.