Analysis of the Characteristics and Mechanisms of the Pacific Decadal Oscillation in a Suite of Coupled Models from the Geophysical Fluid Dynamics Laboratory

Abstract

Abstract North Pacific decadal oceanic and atmospheric variability is examined in a suite of coupled climate models developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The models have ocean horizontal resolutions ranging from 1° to 0.1° and atmospheric horizontal resolutions ranging from 200 to 50 km. In all simulations the dominant pattern of decadal-scale sea surface temperature (SST) variability over the North Pacific is similar to the observed Pacific decadal oscillation (PDO). Simulated SST anomalies in the Kuroshio–Oyashio Extension (KOE) region exhibit a significant spectral peak at approximately 20 yr. Sensitivity experiments are used to show that (i) the simulated PDO mechanism involves extratropical air–sea interaction and oceanic Rossby wave propagation; (ii) the oscillation can exist independent of interactions with the tropics, but such interactions can enhance the PDO; and (iii) ocean–atmosphere feedback in the extratropics is critical for establishing the approximately 20-yr time scale of the PDO. The spatial pattern of the PDO can be generated from atmospheric variability that occurs independently of ocean–atmosphere feedback, but the existence of a spectral peak depends on active air–sea coupling. The specific interdecadal time scale is strongly influenced by the propagation speed of oceanic Rossby waves in the subtropical and subpolar gyres, as they provide a delayed feedback to the atmosphere. The simulated PDO has a realistic association with precipitation variations over North America, with a warm phase of the PDO generally associated with positive precipitation anomalies over regions of the western United States. The seasonal dependence of this relationship is also reproduced by the model.