To provide a common framework for evaluating the strengths and weaknesses of regional climate models and their component procedures through systematic, comparative simulations.

Physically based modeling for the purpose of understanding regional climate, climate change, and climate variability is rapidly increasing in sophistication and usage. Application of a variety of models to a wide range of problems within and beyond the developed countries suggests that interest in this technique will likely continue to grow. These applications go beyond simply modeling the local weather for extended periods and aim at simulating the regional, coupled system of land, atmosphere, ocean, cryosphere and biosphere processes. Accordingly, diagnosis of these models typically includes monthly or longer period statistics of means, variances and extremes of targeted fields. These models have been and will continue to be focal points for both theoretical and applied research.

A useful approach for improving regional climate simulations is the comparison of simulations produced by different models with each other as well as with available observations. Strengths and weaknesses of model structures, numerics and parameterizations can be assessed side-by-side. The utility of model intercomparisons is greatly enhanced if the models operate under the same external constraints, such as dynamic and radiative input across model boundaries. To this end, participants in the Project to Intercompare Regional Climate Simulations (PIRCS) will perform a common set of simulations with regional climate models and produce a common output set, both designed to highlight strengths and weaknesses of individual models and of this general approach to simulating regional climate.

This intercomparison activity continues under the auspices of Iowa State University. PIRCS will seek involvement of scientists from a wide range of countries. PIRCS will promote this involvement by establishing straightforward access for interested researchers to model output and verification data sets generated for the project by its participants. In addition, PIRCS will facilitate the development of collaborations between modeling groups and researchers in developing countries who wish greater involvement in regional climate modeling.

PIRCS will also seek to coordinate its activities with related international programs occurring under the auspices of the World Meteorological Organization's Working Group on Numerical Experimentation, the Global Energy and Water Cycles Experiment (GEWEX), and the U.N. Food and Agriculture Organization. Specific programs include the Comparison of Mesoscale Prediction and Research Experiments (COMPARE), the Atmospheric Model Intercomparison Experiment (AMIP), the Project for Intercomparison of Land-surface Parameterization Schemes (PILPS), and the GEWEX Numerical Experimentation Panel (GNEP). The baseline of experience in these and other groups will facilitate productive evolution of PIRCS. Through this coordination, PIRCS will become a focal point for research and discussion revolving around regional climate simulation.

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