Lidar observations of high altitude cirrus clouds near the tropical tropopause

The physical properties of high altitude cirrus occurring near the tropical tropopause are studied at the tropical station Gadanki (13.5°N, 79.2°E) using a monostatic lidar. This study indicates that the altitude region 14–16 km is more favourable for the formation of cirrus. The cloud depth varies from 0.4 to 4 km. Clouds with optical depth less than 0.03 (subvisual cirrus) is found to occur quite frequently at this tropical region. They introduce significant depolarisation for backscatter radiation indicating the presence of non-spherical ice crystals. Formation and persistence of these clouds is found to be closely associated with the strength of tropospheric turbulence, estimated from vertical wind data obtained from MST radar.