Variations of tidal waves in the Mesosphere and Lower Thermosphere over China region

Wind observations by Meteor radars from the year of 2009 to 2018 are utilized to knowledge the climatological characteristics at Mohe (53.1N), Beijing (40.3N), Wuhan (30.5N), Kunming (25.6N) and Sanya (18N). The tidal components with the period of 24h (diurnal), 12h (semidiurnal) are derived by the decomposition of observations using harmonic fitting method. The results show that the magnitude of diurnal tidal amplitude in the zonal and meridional winds increases with decreasing latitude, especially for the meridional wind. Annual and semi-annual changes dominate the main features. However, large difference of annual and semi-annual changes between the zonal and meridional could be seen clearly. Moreover, the diurnal tidal amplitude in the zonal wind at Mohe shows opposite changes above 90km and below 88 km, which is that the amplitude displays large value below 88km during February and March, while small value is prevailing above 90km during this time. When the diurnal amplitude above 90km is large accompanying with small value below 88 km. For the semidiurnal tide, the annual variation is clearly found for the zonal and meridional winds in their amplitudes at all stations. Meanwhile, the magnitude of semidiurnal tidal amplitude decreases with decreasing latitude, and that of meridional amplitude is larger than that of zonal amplitude. At all stations, the zonal diurnal tidal amplitude at Wuhan is largest above 88km in Spring and 94 km in Summer, that at Kunming is largest below 92 km in autumn and winter. The meridional diurnal amplitude at Sanya is biggest above 88 km in four seasons, and that at Kunming is biggest below 86 km in four seasons. For all seasons, the amplitudes in the zonal and meridional winds at Mohe are smallest. For the zonal wind, semidiurnal tidal amplitude at Beijing is largest at 82 – 94 km in Spring, 82 – 96 km in Summer, above 92 km in Autumn. Meantime, the semidiurnal tidal amplitude at Mohe is larger above 94 km and below 82 in Spring, above 96 km and 82 km in Summer, below 90 km in Autumn and at all heights in Winter. Simultaneously, the semidiurnal tidal amplitude at Sanya is smallest in Spring, Summer, Autumn and above 98 km in Winter. However, the variation of meridional semidiurnal tidal amplitude becomes complicated.