Interdecadal Modulation of ENSO-Related Anomalous Equatorial Intermediate Currents in the Western Pacific by the PDO

Abstract

As the most prominent decadal variability in the Pacific Ocean, the Pacific Decadal Oscillation (PDO) can influence the El Niño-Southern Oscillation-related atmospheric and upper oceanic motions. Based on results from ocean reanalysis products and linear continuously stratified model experiments, we reveal that the PDO can further extend its interdecadal modulation effect to the equatorial intermediate currents below the thermocline. For the maximum El Niño-related intermediate eastward transport anomaly in the western Pacific, its magnitude during the warm PDO is nearly twice as large as that during the cold PDO, and its occurrence time in the warm PDO leads that in the cold PDO by about 2 months. Such modulation is achieved through westward and downward propagation of the reflected Kelvin-to-Rossby waves, triggered by enhanced and eastward-displaced anomalous westerly wind. The decisive wind forcing region for the modulation is located over the equatorial central Pacific of 5°S–5°N and 180°–140°W.