Variability and anisotropy of mesospheric wind spectra

The winter mesosphere over Japan was observed with the new MF radars at Wakkanai (45.4 degrees N, 141.7 degrees E) and Yamagawa (31.2 degrees N, 130.6 degrees E). The wind spectra show dominance of different tidal waves at the two sites at the same time. The temporal evolution of the wind spectra is suggestive of resonant nonlinear interactions between planetary waves, tides, and gravity waves. At Wakkanai, the decay of the 24-h and 12-h waves was observed in the spectra of the zonal wind component. It is remarkable that the 12-h wave of the meridional wind component remained strong while the zonal 12-h wave disappeared. Further anisotropies of the meridional and zonal frequency spectra are described, as well as the slopes of the wind power spectra.