A statistical study of sporadic sodium layer observed by Sodium lidar at Hefei (31.8° N, 117.3° E)

Sodium lidar observations of sporadic sodium layers (SSLs) during the past 3 years at a mid-latitude location (Hefei, China, 31.8° N, 117.3° E) are reported in this paper. From 64 SSL events detected in about 900 h of observation, an SSL occurrence rate of 1 event every 14 h at our location was obtained. This result, combined with previous studies, reveals that the SSL occurrence can be relatively frequent at some mid-latitude locations. Statistical analysis of main parameters for the 64 SSL events was performed. By examining the corresponding data from an ionosonde, a considerable correlation was found with a Pearson coefficient of 0.66 between seasonal variations of SSL and those of sporadic E (Es) during nighttime, which was in line with the research by Nagasawa and Abo (1995). From comparison between observations from the University of Science and Technology of China (USTC) lidar and from Wuhan Institute of Physics and Mathematics (WIPM) lidar (Wuhan, China, 31° N, 114° E), the minimum horizontal range for some events was estimated to be over 500 km