Observed and Simulated Structure of the Tropical Tropopause Layer and processes that maintain the TTL

The structure and variability of the Tropical Tropopause Layer (TTL) are analyzed in detail in multiple global coupled chemistry climate models, and compared to recent observations from field campaigns, radiosondes and satellites. The relationships between water vapor, clouds, ozone and the thermal structure of the TTL are examined in models and observations. The results indicate that the thermal structure of the TTL is well reproduced by global models. Variability of the TTL is also reproduced by global models at the scales they can resolve. The models broadly reproduce observed relationships between clouds and the thermal structure, and clouds and the trace gas structure (ozone and water vapor). Model deficiencies regarding clouds and small scale structure are discussed. The results and diagnostics in the simulations allow us to make conclusions regarding the role of transport, radiation and convection in regulating the variability and mean structure of the TTL.