Tropical-Extratropical Exchange Based on Argo Profiles and Ship-Based Observations Near the Western Boundary

Abstract:

The tropical-extratropical exchange in the northwestern Pacific Ocean is studied using the absolute geostrophic currents based on Argo Profiles and the observations of the western boundary currents (WBCs) during two cruises in the winters of 2010 and 2012. The absolute geostrophic currents are calculated using the P-vector method for the period of 2004 through 2011. The transport of the geostrophic currents is compared with the Sverdrup theory and found to differ significantly in several locations. Analyses have shown that errors of wind stress estimation cannot account for all of the differences. The largest differences are found in the area, where nonlinear activities are vigorous. It is, therefore, suggested that the linear dynamics of the Sverdrup theory is deficient in explaining the geostrophic transport of the tropical northwestern Pacific Ocean.

Previous studies suggest recharge and discharge of the tropical Pacific Ocean heat content through the interior circulation of the North Pacific Ocean, based on the Sverdrup theory, and that the WBCs play the role opposite to the interior ocean recharge and discharge anomalies. Using ocean observations from two cruises in a La Niña winter and a normal winter, it is suggested that the Kuroshio transport decreases significantly and the Mindanao Current transport increases significantly at the peak of 2010 La Niña, opposite to the prediction of existing theory. The anomalies of the western boundary current transport are found much larger than those of the meridional circulation in the entire interior of the North Pacific Ocean, the dynamics of which are suggested to be associated with the Kelvin wave propagation around the Philippine islands. The results suggest that the WBCs dominate the interannual recharge and discharge of the western Pacific warm pool during the 2010 La Niña.