as a “loosely unified” system, in that neither the coupled model development nor the metrics used to assess it currently feed back into changes in the GFS weather-forecast model. A 30-year coupled reanalysis at 50 km horizontal resolution, CFSR, has been performed using CFSv2 (Saha et al., 2010); this is a major additional contribution to climate data that takes advantage of a coupled climate-capable modeling system with cutting-edge assimilation capabilities, and which should help engage the outside community in the CFS effort.

Finding 11.4: Three lessons stand out from examining existing unified modeling systems:

•  a unified model can be world leading for both weather and climate simulation;

•  successful climate and weather modeling groups that share a unified or near-unified model require a strong supportive management and adequate dedicated resources that can bridge between the different goals and user needs of weather and climate models; and

•  unified models are attractive to outside users because of their flexibility and multiscale validation, and help promote interactions between the modeling center and a broad user community whose feedback can improve the model.


Unified Modeling

The committee recommends an accelerated national seamless modeling effort that spans weather to climate time scales. One method to achieve this would be nurturing a U.S. unified weather-climate prediction system capable of state-of-the-art forecasts from days to decades, climate-quality data assimilation, and reanalysis. This prediction system would be a collaboration among operational weather forecast centers, data assimilation centers, climate modeling centers, and the external research community. In particular, it is important to develop it as a partnership between the research and operational communities to best leverage off existing expertise. Versions of this unified model might be deployed as part of an operational prediction system, but it should also be supported for use as a research model.

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