2002 Annual

Thursday, 17 January 2002: 9:45 AM
Tropospheric Temperature Sensitivity from the AMIP II Experiment
Justin Jay Hnilo, LLNL, Livermore, CA; and J. R. Christy
The Atmospheric Model Intercomparison Project (AMIP) offers one the unique opportunity to examine various state of the art General Circulation Models (GCMs) which are all forced with the same boundary conditions. With the success of the AMIP I experiment (7901-8812) a new project was initiated AMIP II, which uses improved boundary conditions as well as integrates over a longer period of time (7901-9603). AMIP I and II offer one the unique opportunity to quantify evolutionary improvements in modeling and our understanding of atmospheric processes as well as, documenting modeled systematic errors. These data are archived and maintained by PCMDI.

Within this work emphasis will be placed on the examination of surface, pressure-level and deep-layer temperatures (e.g., observed and simulated Microwave Sounding Unit Temperatures). Our work addresses measures of sensitivity, coupling and surface-troposphere coherence from both observational estimates (e.g., reanalysis) as well as, atmospheric models. These results will illuminate model improvements and areas of both model and observed uncertainty.

Through the examination of both surface and pressure-level temperatures we are able to quantify a model's ability to represent observed surface to tropospheric coupling/decoupling, decadal trends and measures of temperature coherence. Observational quantities are obtained by using data from the NCEP/NCAR, NCEP/DOE and ERA15 reanalyses. Our results indicate that the AMIP II models and reanalyses data have quite different zonal-mean pressure level temperature trends. The AMIP II models demonstrate a consistent lower tropospheric warming in excess of the surface boundary forcing (SSTs) and this warming is inconsistent throughout the modeled atmospheric column. Measures of surface to troposphere temperature sensitivity for the AMIP II models show more sensitivity than derived by the observational estimates. This means that per degree of skin temperature warming the models have a greater tendency to warm in the troposphere than do the observations. Results show a substantial quantitative difference in the strength of surface/lower-tropospheric temperature coupling between observations and models. Our results highlight the ranges that exist in these measures of sensitivity in both observational estimates and models.

This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

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