Lidar observations of cirrus cloud near the tropical tropopause: general features

General features of high-altitude cirrus clouds observed below the tropical tropopause are studied using lidar at Gadanki (13.5°N, 79.2°E). These clouds occur quite frequently over this tropical region. Thin clouds with optical depth <0.3 are found to occur more frequently than dense clouds with optical depth >0.3. The preferred altitude of these clouds is between 14 and 16 km, with a vertical extent ranging from 0.4 to 4 km. The backscattered lidar signal from the thin cirrus clouds exhibits significant depolarisation, indicating the presence of randomly oriented nonspherical ice crystals in abundance.