Nighttime and Seasonal variations of the Sodium Layer Measured by Lidar at Different Latitudes in China

AbstractThis study is based on long‐term observations of the sodium layer by lidars at Beijing (40.47°N, 115.97°E), Hefei (31.87°N, 117.23°E) and Hainan (19.99°N, 110.34°E), which are part of the Meridian Project of China. The purpose is to reveal characteristics of nighttime and seasonal variations of the background sodium layer over China along 120°E. The observations from three lidar stations on Dec. 17, 2010 show that, the nighttime variations of the sodium layer are not correlated to each other. The fitted long‐term variations with annual plus semiannual changes reveal that the column abundance of the sodium layer over Beijing and Hefei varied annually, while that over Hainan changed semiannually. The seasonal variations of centroid heights and RMS widths of the sodium layer present apparent semiannual variation tendency, excluding the long‐term change of RMS width for Hainan. Statistics illustrate that the seasonal variations of column density of background sodium layer is correlated with the change of temperature near the mesopause. It has the maximum in winter and minimum in summer, respectively. With the growth of the latitude, the column abundance increases and the annual variation tendency becomes more obvious. There is no clear latitude dependence on the centroid height of the sodium layer, and it changes semiannually with seasons at three locations. The RMS width of the sodium layer is the largest at Beijing (middle and upper latitude) and the least at Hefei (middle latitude) in every month of one year, and it is the medium at Hainan (lower latitude).