Diurnal and semidiurnal tide in the upper middle atmosphere during the ®rst year of simultaneous MF radar observations in northern and southern Japan (45°N and 31°N)

The climatology of mean wind, diurnal and semidiurnal tide during the ®rst year (1996±1997) of simultaneous wind observations at Wakkanai (45.4°N, 141.7°E) and Yamagawa (31.2°N, 130.6°E) is presented. The locations of the radars allow us to describe the latitudinal dependence of the tides. Tidal amplitude and phase pro®les are compared with those of the global scale wave model (GSWM). While the observed amplitude pro®les of the diurnal tide agree well with the GSWM values, the observed phase pro®les often indicate longer vertical wavelengths than the GSWM phase pro®les. In contrast to the GSWM simulation, the observations show a strong bimodal structure of the diurnal tide, with the phase advancing about 6 hours from summer to winter.