High supersaturation inside cirrus in well-developed tropical tropopause layer over Indonesia

The relationship between relative humidity and cirrus clouds in the tropical tropopause layer (TTL) is investigated using balloon-borne cryogenic frostpoint hygrometers (CFH) and quasi-collocated measurements of space-borne Cloud- Aerosol Lidar with Orthogonal Polarization (CALIOP) over Biak (1.17°S, 136.06°E) and Kototabang (0.20°S, 100.32°E) both in Indonesia in Januaries 2007 and 2008. At Kototabang, thin layers of high supersaturation, up to ∼160% in relative humidity with respect to ice (RHi), are often observed co-existing with cirrus clouds at altitudes of ∼15-18 km. At Biak, RHi inside cirrus is around 100% or less without large supersaturation layers, and most clouds are limited to altitudes below 16 km. We found that the presence and the degree of supersaturation may strongly depend on the phases of large-scale disturbances such as the MJO rather than geographical difference.