Climatology of mesopause region nocturnal temperature, zonal wind, sodium density, and GW momentum flux observed by sodium lidar over Hefei, China (32°N, 117°E)

The University of Science and Technology of China narrowband sodium temperature/wind lidar, located in Hefei, China (32°N, 117°E), has made routine nighttime measurements since January 2012. 154 nights ( 1400 hours) of vertical profiles of temperature, sodium density, and zonal wind, and 83 nights ( 800 hours) of vertical flux of gravity wave (GW) zonal momentum in the mesopause region (80-105 km) have been obtained during the period from 2012 to 2016. In temperature, it is most likely that the diurnal tide dominates below 100 km in spring, while the semidiurnal tide dominates above 100 km throughout the year. A clear semiannual variation in temperature is revealed near 90 km, in phase with the tropical mesospheric semiannual oscillation (MSAO). The variability of sodium density is positively correlated with temperature below 95 km, suggesting that in addition to dynamics, the chemistry also plays an important role in the formation of sodium atoms. The seasonal variability of sodium density observed by both lidar and satellite generally agrees well with a whole atmosphere model simulation using an updated meteoric input function which includes different cosmic dust sources. In zonal wind, the diurnal tide dominates in both spring and fall, while semidiurnal tide dominates in winter. The observed semiannual variation in zonal wind near 90 km is out-of-phase with that in temperature, consistent with the tropical MSAO. The lidar observations generally agree with satellite and meteor radar observations as well as model simulations at similar latitude. The 50-70% of zonal momentum flux is induced by short-period (10 min - 2 hr) GWs. The large zonal momentum flux in summer and winter due to short-period GWs are clearly anti-correlated with eastward zonal wind maxima below 90 km, suggesting the filtering of short-period GWs by the SAO wind.