Wednesday, 12 January 2005: 1:30 PM
The Global Land-Atmosphere Coupling Experiment (GLACE): Model characteristics and comparison
The Global Land-Atmosphere Coupling Experiment (GLACE), a joint project of the GEWEX Global Land Atmosphere System Study (GLASS) and the CLIVAR Working Group on Seasonal-to-Interannual Prediction (WGSIP), provides a unique look at how land surface variables influence atmospheric processes in a number of atmospheric general circulation models (AGCMs). At present, a dozen AGCM groups have completed the same highly-controlled numerical experiments for GLACE, experiments specifically designed to quantify a model's land-atmosphere coupling strength. The general features of the coupling and the extent to which coupling strength varies among the participating GCMs are evaluated in this study. Analysis of the results shows that while the strength of land-atmosphere coupling varies widely across the models, certain commonalities are observed in the geographic pattern of coupling. It is found that the multi-model "hot spots" of coupling are generally located in the transition zones between wet and dry climates, where the evaporation is both sensitive to soil moisture and high enough to have an impact on rainfall. In some ways, this multi-model estimate of hot spots is the best such estimate attainable, given the sparseness of relevant observational data and the difficulties associated with interpreting such data.
The inter-model differences in coupling strength are studied in terms of soil moisture's ability to affect evaporation and evaporation's ability to affect precipitation. We find that coupling strength tends to be highest in a given region for those models with both a high temporal evaporation variance and a strong control of soil moisture on evaporation.