Spatiotemporal vertical velocity variation in the western tropical Pacific and its relation to decadal ocean variability

Abstract

Abstract Prior to the cold phase of the Pacific decadal oscillation (PDO), sea surface water in the western tropical North Pacific is heated. To evaluate the impact of the subsurface water on the upper-ocean ( $$10^{-6}\,{\text {m\,s}}^{-1}$$ > 10 - 6 m\,s - 1 ) is observed in the region of $$10^{\circ }$$ 10 ∘ – $$17^{\circ }$$ 17 ∘ N, $$140^{\circ }$$ 140 ∘ E– $$180^{\circ }$$ 180 ∘ in the North Equatorial Current, southern part of the North Pacific subtropical gyre. Possibly besides the Ekman upwelling, the upward current contributes to the cooling of the upper ocean in the western tropical North Pacific through the upward advection of the deep cold water. The upward current was found to be intensified (attenuated) by the strengthening (weakening) of the subtropical gyre interior southward flow on the QD timescale in association with frequent occurrences of La Niña (El Niño) events. The weakening of the upward current is responsible for the QD increase in upper-ocean temperature in the western tropical North Pacific, which is equivalent to or larger than $$0.2~^{\circ }$$ 0.2 ∘ C, several years after the warm phase of the PDO. The QD temperature variation may affect the phase reversal of the PDO through the heat transport of the western boundary current of the subtropical gyre, i.e., the Kuroshio.

Keywords

• Western tropical Pacific
• ENSO
• PDO
• Vertical velocity
• P-vector inverse method
• AGEM