79.2 ◦ E)

Abstract. We studied the characteristics of sporadic sodium layers (SSLs) observed with the sodium (Na) resonance scat-tering lidar at Gadanki (13.5 ◦ N, 79.2 ◦ E). The SSLs were observed on a total of 63 occasions during 464 h of Na lidar observations from January 2005 to February 2006. The ob-servations showed that one SSL event occurred, on average, every 7 h. The most prominent sporadic layer, which formed on 12 February 2005, exhibited a peak density of 60 722 Na atoms/cm3 around 92 km and it was nearly twice the peak density reported from elsewhere using ground-based obser-vations. In general, the SSLs exhibited the following char-acteristics: (1) they developed at heights between 88 and 98 km with an average height around 94 km; (2) maximum den-sity occurred during the early morning hours between 02:00 and 05:00 IST; (3) the ratio of the maximum peak Na den-sity to the average density was normally around 3 to 5 and it exceeded even 10 in some cases; (4) the events lasted from a few minutes to several hours. The formation period of the SSLs was longer compared to the decay period of the SSLs. Most of the SSL events showed downward motions