A key role of off-equatorial subsurface temperature anomalies in Tropical Pacific Decadal Variability

Abstract

Abstract We demonstrate the key role of off-equatorial subsurface temperature anomalies in driving the phase transition of Tropical Pacific Decadal Variability (TPDV) using observation and model experiments. During the positive phase of TPDV, anomalous atmospheric responses in the off-equatorial northwestern Pacific induce positive Ekman pumping. The resulting negative subsurface temperature anomaly generated then propagates along the North Equatorial Countercurrent pathway towards the central basin, causing a sign reversal of the equatorial sea-surface temperature anomalies around three years later. Moreover, the positive phase of TPDV possibly changes the state of the Kuroshio Extension through tropical-extratropical interaction, which subsequently projects onto the footprint of the Pacific Meridional Mode, thereby amplifying subsurface-produced disturbance 0–12 months before the cold peak phase. The cold phase is completely established after five years. Similarly, the same dynamic applies to the reversed phase, leading to a preferred decadal oscillation driven by off-equatorial subsurface temperature anomalies and extratropical-tropical ocean-atmosphere interaction.