Lidar observations of cirrus clouds at low latitude tropical station, Trivandrum (8°33′n, 77°E):: General characteristics

High altitude cirrus clouds were observed at a low latitude station, Trivandrum using the monostatic high power pulsed Nd: YAG lidar operating at 532 nm during the period from June 1999 to April 2003. During this period, 190 days of observations were made and cirrus clouds were detected in about half of the cases. An analysis of lidar data had shown that the occurrence of such clouds near the tropopause is quite frequent. It is found that the Sub visible clouds and thin clouds together constitute 78% of total cirrus Cloud seasonal occurrences. Optically thick cirrus clouds occur more frequently during the summer monsoon period compared to other seasons. It is observed that in majority of the cases cloud top temperature was between -70 to -80degreesC. Also, the variation of the geometrical depth with optical depth has been studied.