Identifying the top of the tropical tropopause layer from vertical mass flux analysis and CALIPSO lidar cloud observations

We identify the top of the tropical tropopause layer (TTL) by analyzing the vertical mass flux profile based on radiative transfer calculations employing observed atmospheric profiles and cloud information. We find that the top of the TTL is located at similar to 18.7 km ( 70 mb). We have analyzed the CALIPSO lidar cloud observations from June 2006 to February 2007, which indicates that almost no clouds occur above 19 km, consistent with the top of TTL based on vertical mass flux analyses. The total cloud fractions between 20 degrees S and 20 degrees N are about 0.05% at 18.5 km, 0.5% at 18.0 km and 5% at 17.0 km, where the clouds with optical depth larger than 0.5 contribute up to one tenth of these total cloud fractions. The clouds above 17 km mainly originate over the West Pacific, South America, Central Africa, and South Asia.