Climate impacts of the Atlantic Multidecadal Oscillation simulated in the CMIP5 models: A re-evaluation based on a revised index

The Atlantic Multidecadal Oscillation (AMO) has pronounced influences on weather and climate across the globe. This study provides a direct comparison of the observed AMO-related surface temperature and precipitation anomalies to those simulated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. It is found that the model-simulated AMO-related features are obscured by the global signal in some key regions if the North Atlantic sea surface temperature (SST) itself is used to represent the AMO as in previous studies. After the global mean SST is removed from the North Atlantic SST, the CMIP5 models show substantially better agreement with the observations in terms of the AMO-related worldwide impacts, such as the Pacific SST and the rainfall over the United States and India. These results suggest the removal of the global signal or signals originating in other ocean basins is a necessary procedure to uncover the AMO features in climate model simulations.