Lidar observation campaigns on diurnal variations of the sodium layer in Beijing and Wuhan, China

Based on observations from daytime lidars in eastern China, diurnal cycles of the sodium layer over Wuhan (30.5°N, 114.6°E) and Beijing (40.5°N, 116°E) are investigated. Diurnal variations of Na density, root mean square (RMS) layer width, and centroid height of the sodium layer are analyzed. Results reveal that the large diurnal cycles of the sodium layer are controlled mainly by 24-hr oscillations at the two observation sites. The diurnal variation of the sodium layer over Wuhan was modulated mainly by tidal perturbations during the lidar observation campaign. Conversely, the diurnal variation over Beijing was controlled principally by photoionization and photochemistry effects during another campaign, and there was little evidence of direct tidal perturbations. These comparisons suggest that the diurnal variation of the sodium layer perhaps has obvious regional characteristics across China. The variation can be either controlled mainly by tidal perturbations or by photoionization and photochemistry effects in different seasons.