Toward A Practical Implementation of An Interactive Multi-Model With Full GCM's

It has been shown that the performance of coupled ocean-atmosphere models can be improved by allowing different models to exchange different flux components at the ocean- atmosphere interface. On theoretical grounds, we expect improvement from the run-time coupling of different models generally, as compared to what might be obtained simply by averaging model outputs, even with carefully chosen weights. It is therefore desired to allow a handful of climate models to exchange information from a given set of corresponding variables freely as the models run. NCAR's Data Assimilation Research Testbed (DART) can serve as an inter-model coupler, apart from any data assimilation capability. A variable in any model, either in the atmosphere or ocean component, can thus be "nudged" by a corresponding variable from any other model. Relatively few operations are involved in the coupling, so the computational cost is simply the sum of the costs of running the different models. Contrary to some premonitions, an inter-active multimodel with full GCM's is thus readily achievable using current software. The coupling is illustrated for suites of models of varying complexity.