Variability of the Climate System

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AbstractATM-9907915SchneiderThe project is designed to enhance understanding of the variability and predictability of the current climate, especially that associated with the North Atlantic Oscillation (NAO), on inter-seasonal to inter-decadal time scales. Since it is impossible to do the type of controlled experiments necessary to accomplish this goal in the actual global climate system, a coupled GCM (general circulation model) that simulates the observed climatology and variability realistically will be the basic tool for the investigation.The climate will be represented by a multi-century control simulation with an updated version of the COLA (Center for Atmosphere-Ocean Land Studies) global coupled GCM. The COLA coupled GCM produces a realistic simulation of many aspects of low frequency climate variability, including interannual and decadal El Nino/La Nina, and the North Atlantic, North Pacific, and Arctic/Antarctic Oscillations. A series of experiments in which the GCM is modified will be made to help understand the mechanisms underlying the NAO variability found in the control simulation. These experiments will utilize the anomaly coupling capabilities of the GCM to allow one-way or fully coupled atmosphere-ocean or atmosphere-land interactions in localized regions, while specifying climatological boundary conditions elsewhere. The mechanisms that will be examined are local atmosphere-ocean coupling, local ocean dynamics, remote influence of tropical SST anomalies, coupled atmosphere-land processes, and the role of stochastic atmospheric forcing. The project has the potential to advance knowledge in several important areas. These are: 1) understanding low frequency NAO associated variability; 2) indicating whether this type of internal climate variability is or is not predictable; 3) evaluating whether internally generated climate variability is sufficient to explain observed variability over the North Atlantic over the last century, or whether alternative explanations must be sought; 4) developing and evaluating a new class of experiments to understand climate variability in coupled CMS.