GEWEX Cloud System Study (GCSS)
Background
There are a variety of cloud processes that affect the large-scale behavior of the climate system, but occur on scales too small to be represented explicity in global numerical models used for climate and weather prediction. Scientists develop numerical representations or parameterizations to represent the behavior of these processes. It is generally recognized that inadequate parameterization of clouds is one of the greatest sources of uncertainty in the prediction of weather and climate.
GCSS is developing better parameterizations of cloud systems for climate models by improving understanding of the physical processes at work within the following types of cloud systems: (1) boundary layer, (2) cirrus, (3) polar and (4) precipitating convective. There are GCSS working groups for each of these cloud systems. In addition, there are working groups that cover cloud climate feedbacks, cloud microphysics, and the GCSS-Pacific Cross-Section Intercomparison. Each of these working groups has adopted single-column modeling as a key research strategy, and each is also making use of cloud ensemble models. The CFMIP-GCSS Intercomparison of LES and SCMs is a new study under the cloud feedbacks working group.
The GCSS working groups are performing the following activities:
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Identifing and developing cloud-resolving and mesoscale models appropriate for each cloud system type.
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Specifing blueprints of minimum observational requirements for the development and validation of these models.
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Assembling, for particular cloud types, case-study data sets accessible to the community of (a) matched observations from satellites, surface and aircraft, and (b) mode-derived synthetic data sets.
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Conducting workshops, including model intercomparisions using the above case study data sets.
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Using the data sets to derive a better understanding of the coupled processes within different types of cloud systems and to derive improved parameterization schemes for large-scale models.
- Develop the scientific basis for the parameterization of cloud processes.
- Highlight key issues and encourage other relevant programs to address them.
- Promote the evaluation and intercomparision of parameterization schemes for cloud processes.
Dr. Jon Petch, co-chair
UK Met Office
Exeter, UK
Dr. Chris Bretherton, co-chair
Director, UW Program on Climate Change
Professor, Atmospheric Sciences & Applied Math
University of Washington
Seattle, Washington USA
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