Abstract

Results are described from a large sample of coupled ocean–atmosphere retrospective forecasts during 1980–2006. The prediction system is based on the National Center for Atmospheric Research (NCAR) Community Climate System Model version 3 (CCSM3.0) and a state-of-the-art ocean data assimilation system made available by the National Ocean and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory (GFDL). The retrospective forecasts are initialized each January and July of each year, and ensembles of six forecasts are run for each initial month, yielding a total of 324 1-yr predictions. In generating the ensemble members, perturbations are added to the atmospheric initial state only. The skill of the prediction system is analyzed from both a deterministic and a probabilistic perspective and is compared to the operation NOAA Climate Forecast System (CFS). The CCSM3.0 SSTA forecasts have notable westward phase propagation, which is consistent with the errors in the “free running” model. The CCSM3.0 forecasts appear to do a better job than CFS on the transition from warm to cold SSTA. This is probably due to the fact that the CFS tends to persist warm events longer than observed. The CCSM3.0 also appears to be more confident than CFS in forecasting cold events. In terms of Nino3.4 forecast skill, both models have comparable skill that appears to be complementary. Most importantly, combining both models into a multi-model ensemble is superior to either model individually.

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