Constraint of Air-Sea Interaction Significant to Skillful Predictions of North Pacific Climate Variations

The Pacific decadal oscillation (PDO) is the most dominant decadal climate variability over the North Pa-cific and has substantial global impacts. However, the interannual and decadal PDO prediction skills are not satisfactory, which may result from the failure of appropriately including the North Pacific midlatitude air-sea interaction (ASI) in the initialization for climate predictions. Here, we present a novel initialization method with a climate model to crack this nut-shell and achieve successful PDO index predictions up to 10 years in advance. This approach incorporates oceanic observa-tions under the constraint of ASI, thus obtaining atmospheric initial conditions (ICs) consistent with oceanic ICs. During predictions, positive atmospheric feedback to sea surface temperature changes and time-delayed negative ocean circulation feedback to the atmosphere over the North Pacific play essential roles in the high PDO index prediction skills. Our findings highlight a great potential of ASI constraints during initialization for skillful PDO predictions. SIGNIFICANCE STATEMENT: The Pacific decadal oscillation is a prominent decadal climate variability over the North Pacific. However, accurately predicting the Pacific decadal oscillation remains a challenge. In this study, we use an advanced initialization method where the oceanic observations are incorporated into a climate model constrained by air-sea interactions. We can successfully predict the Pacific decadal oscillation up to 10 years in advance, which is hardly achieved by the state-of-the-art climate prediction systems. Our results suggest that the constraint of air-sea in-teraction during initialization is important to skillful predictions of the climate variability on decadal time scales.