First report of sporadic K layers and comparison with sporadic Na layers at Beijing, China (40.6°N, 116.2°E)

摘要

A double-laser beam lidar was successfully developed to simultaneously measure K and Na layers at Beijing (40.6°N, 116.2°E) in 2010. Statistical analysis of the parameters of sporadic K (K_s) and sporadic Na (Nas) layers was performed over 2 years of lidar data, and different characteristics of them were found. The average K_s occurrence (2.9%) was lower than that of Nas (5.9%); the Nas occurrence had a maximum (19.3%) in May–June months and a minimum (1.6%) in January–February months, while the K_s occurrence had a maximum (4.9%) in January–February months and a minimum (1.0%) in September–October months; most Ks peaks tended to occur around 93 km, which was ~2 km lower than that of Nas (~95 km); the Ks peak density was often at least 1 order of magnitude lower than that of Nas; notably, two K_s with high peak densities (>1000 cm~(-3)) were observed, which were much higher than K density (15–300 cm~(-3)) reported before. The ascending time of Ks was often longer than its descending time, but an opposite trend occurred for Nas. During the 152 cases of joint observation for the K and Na layers, 21% (32/152) were cases in which Ks and Nas events simultaneously occurred, while 79% (120/152) were cases in which only one layer (K or Na) exhibited a strong K_s or Nas.