Study on average characteristics of upper boundary of sodium layer in Yanqing, Beijing

In this paper, data from the sodium fluorescence lidar of Yanqing, Beijing (116. 0 degrees E, 40. 5 degrees N) for the night of November 2018-December 2019 were analysed at resolution of 1 km and 1 hour. The range of heights that can be reached at the upper boundary of the sodium layer, its corresponding seasonal variability, and nighttime evolution were obtained: the probabilities that the top sodium layer in Yanqing can reach 110 km, 120 km and 130 km are 99. 94%, 84. 46% and 40. 34%, respectively, leading to the conclusion that the top sodium layer can reach 120 km in most cases, breaking the traditional view that the top sodium layer is at 105 km (or 110 km); the seasonal pattern of the upper boundary is highest in May-June and lowest in February-March; the density of the top sodium layer increases during the second half of the night. We compare the correlations of sporadic sodium layer, temperature and meteor injection with the upper boundary altitude range and conclude that sporadic sodium layer contributes significantly to the expansion of the upper boundary of the sodium layer, followed by temperature and meteor injection. Moreover, the increased meteor injection in the latter half of the night correlates with the increased density of the top sodium layer at this time. The study of the ability to increase the top sodium layer to 120 km may provide a theoretical basis for extending the detection height of the wind temperature.