Quantifying the top of the tropical tropopause Layer from observations

We have quantified the top of the tropical tropopause layer (TTL) by analyzing the vertical mass flux profiles above 17 km based on the radiative transfer calculations. The observed atmospheric profiles including the temperature, water vapor, and ozone for the input of the radiation calculations were from Southern Hemisphere Additional Ozonesondes (SHADOZ) for 1998-2005. The observed cloud information from International Satellite Cloud Climatology Project (ISCCP) was employed to account for the impact of tropospheric clouds on the radiative heating rate above 17 km. We find that the top of the TTL is located at about 18.7 km (~70 mb). The magnitude of the vertical mass flux decreases with height substantially in the TTL before reaching its top region. The top of the TTL is the bottom of the near constant mass flux region. We have analyzed the CALIPSO lidar cloud observations from June 8, 2006 to February 28, 2007. It is found that almost no clouds occur above 19 km, consistent with the top of the TTL based on vertical mass flux analyses. It is found that the total cloud fractions between 20oS and 20oN are about 0.1% at 18.5 km, 1% at 18.0 km and 10% at 17.0 km, where the clouds with optical depth larger than 0.5 contribute to one tenth of these total cloud fractions. The clouds above 17 km are mainly originated over West Pacific, South America, Central Africa, and South Asia.