The role of the redistribution of tropical upper tropospheric humidity in the formation of tropical cirrus is studied using three years (June 2006 to December 2008) of observations with the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) as well as the Microwave Limb Sounder (MLS) onboard the Aura satellite. The National Centers for Environmental Prediction and Atmospheric Research reanalysis data are also used. Results show that the redistribution of upper tropospheric humidity from a highly convective zone to the Indian peninsular region leads to the formation of the tropical cirrus. Advection of upper layer humidity is caused by the tropical easterly jet (TEJ) associated with the Asian summer monsoon (ASM). Thus the present analysis brings out, for the first time, the role of the TEJ in the redistribution of upper tropospheric humidity and consequently in the formation of tropical cirrus. As little observational evidence exists in support of the generative mechanisms of the cirrus, the present results can be useful in quantifying the formation process of these clouds, which have implications for Earth's radiation budget and improving global climate models.
