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PCMDI > WCRP CMIP3 Model Output > Diagnostic Subprojects Printer Friendly Version
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  • Cordero, E. C. and P. M. de F. Forster, 2006: Stratospheric variability and trends in models used for the IPCC AR4. Atmos. Chem. and Phys., 6, 5369–5380.

Atmosphere and ocean general circulation model
(AOGCM) experiments for the Intergovernmental Panel on
Climate Change Fourth Assessment Report (AR4) are analyzed
to better understand model variability and assess the
importance of various forcing mechanisms on stratospheric
trends during the 20th century. While models represent the
climatology of the stratosphere reasonably well in comparison
with NCEP reanalysis, there are biases and large variability
among models. In general, AOGCMs are cooler than
NCEP throughout the stratosphere, with the largest differences
in the tropics. Around half the AOGCMs have a top
level beneath 2 hPa and show a significant cold bias in
their upper levels (10 hPa) compared to NCEP, suggesting
that these models may have compromised simulations near
10 hPa due to a low model top or insufficient stratospheric
levels. In the lower stratosphere (50 hPa), the temperature
variability associated with large volcanic eruptions is absent
in about half of the models, and in the models that do include
volcanic aerosols, half of those significantly overestimate the
observed warming. There is general agreement on the vertical
structure of temperature trends over the last few decades,
differences between models are explained by the inclusion
of different forcing mechanisms, such as stratospheric ozone
depletion and volcanic aerosols. However, even when human
and natural forcing agents are included in the simulations,
significant differences remain between observations
and model trends, particularly in the upper tropical troposphere
(200 hPa–100 hPa), where, since 1979, models show
a warming trend and the observations a cooling trend.

Full Article: http://www.atmos-chem-phys.net/6/5369/2006/

Last Updated: 2007-05-29

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