First report of sporadic Na layers at Qingdao (36° N, 120° E), China
Abstract. This paper reports, for the first time, observational results of mesopause sporadic Na (Nas) layers by a ground-based lidar at Qingdao (36° N, 120° E), China. Based on ~ 430 h of observational data on 95 nights from December 2007 to June 2012, we have selected a total of 53 Nas layer events. It is found that characteristics of Nas layers over Qingdao have general similarity with those over nearby sites, Wuhan (30° N, 114° E) and Hefei (32° N, 117° E), but not those over the site Hachioji (35° N, 139° E) at nearly the same latitude as Qingdao. At the same time, parameters of sporadic E (Es) layers were recorded by an ionosonde. The fact that Es layer occurrence probabilities of 19, 22, and 18% in time intervals before, during, and after the Nas layers are very close to the average occurrence ratio of the nocturnal Es layer (21%), may reveal a general independence between Nas and Es layers over Qingdao. Only those strong Nas layers above the peak altitude of the main Na layer might have a significant correlation with Es layers. In addition, a total of 11 high-altitude (above 105 km) Nas layer events have been surveyed specially. It is found that these high-altitude Nas layers were usually weak. And they possessed long-duration (> 147 min) and broad-layer width (4.0 km) compared with Nas layers below 105 km (> 96 min and 2.4 km). These characteristics are in accord with observational results at Wuhan. It is suggested that there is little correlation between this kind of Nas layers and Es layers. Finally, the summer topside enhancement phenomenon of Na atoms observed at Qingdao is in accord with several earlier observational results at different sites (18, 30, and 54° N) in the Northern Hemisphere.