The Tropical Tropopause Layer 1960–2100
The representation of the Tropical Tropopause Layer (TTL) in 13 different\nChemistry Climate Models (CCMs) designed to represent the stratosphere\nis analyzed. Simulations for 1960�2005 and 1980�2100 are analyzed.\nSimulations for 1960�2005 are compared to reanalysis model output.\nCCMs are able to reproduce the basic structure of the TTL. There\nis a large (10 K) spread in annual mean tropical cold point tropopause\ntemperatures. CCMs are able to reproduce historical trends in tropopause\npressure obtained from reanalysis products. Simulated historical\ntrends in cold point tropopause temperatures are not consistent across\nmodels or reanalyses. The pressure of both the tropical tropopause\nand the level of main convective outflow appear to have decreased\n(increased altitude) in historical runs as well as in reanalyses.\nDecreasing pressure trends in the tropical tropopause and level of\nmain convective outflow are also seen in the future. Models consistently\npredict decreasing tropopause and convective outflow pressure, by\nseveral hPa/decade. Tropical cold point temperatures are projected\nto increase by 0.09 K/decade. Tropopause anomalies are highly correlated\nwith tropical surface temperature anomalies and with tropopause level\nozone anomalies, less so with stratospheric temperature anomalies.\nSimulated stratospheric water vapor at 90 hPa increases by up to\n0.5�1 ppmv by 2100. The result is consistent with the simulated increase\nin temperature, highlighting the correlation of tropopause temperatures\nwith stratospheric water vapor.