In this study, the impact of El Nino/Southern Oscillation (ENSO) variability on the North Atlantic Oscillation (NAO) is examined using the anomaly coupled general circulation model (ACGCM) developed in the Center for Ocean-Land-Atmosphere Studies (COLA). Three experiments are designed: 1) the experiment with global coupling between atmosphere and ocean (control experiment); 2) the experiment being the same as the control experiment except the model atmosphere and ocean are uncoupled in the North Atlantic region, and 3) the experiment being the same as the control experiment except the model atmosphere and ocean are uncoupled in the equatorial Pacific.
The modeled NAO indices from these three experiments are analyzed using various analysis methods. The analysis using traditional methods indicates little effect of ENSO variability on the NAO variability. However, when the modeled NAO indices are decomposed using the recently developed Empirical Mode Decomposition method (EMD), the impact of the ENSO variability on NAO variability on interannual timescale emerges. The variability of SST in the North Atlantic is then shown to be closely tied to the ENSO variability in the tropical Pacific.
The physical mechanism on how the ENSO variability affects the NAO variability is also examined.