Atmospheric Chemistry and Physics, vol. 9, issue 5 (2009) pp. 1621-1637
The representation of the Tropical Tropopause Layer (TTL) in 13 different
Chemistry Climate Models (CCMs) designed to represent the stratosphere
is analyzed. Simulations for 1960�2005 and 1980�2100 are analyzed.
Simulations for 1960�2005 are compared to reanalysis model output.
CCMs are able to reproduce the basic structure of the TTL. There
is a large (10 K) spread in annual mean tropical cold point tropopause
temperatures. CCMs are able to reproduce historical trends in tropopause
pressure obtained from reanalysis products. Simulated historical
trends in cold point tropopause temperatures are not consistent across
models or reanalyses. The pressure of both the tropical tropopause
and the level of main convective outflow appear to have decreased
(increased altitude) in historical runs as well as in reanalyses.
Decreasing pressure trends in the tropical tropopause and level of
main convective outflow are also seen in the future. Models consistently
predict decreasing tropopause and convective outflow pressure, by
several hPa/decade. Tropical cold point temperatures are projected
to increase by 0.09 K/decade. Tropopause anomalies are highly correlated
with tropical surface temperature anomalies and with tropopause level
ozone anomalies, less so with stratospheric temperature anomalies.
Simulated stratospheric water vapor at 90 hPa increases by up to
0.5�1 ppmv by 2100. The result is consistent with the simulated increase
in temperature, highlighting the correlation of tropopause temperatures
with stratospheric water vapor.
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