Exploring the Origins of the Mindanao and Kuroshio Currents in Eddy-Resolving Global Ocean General Circulation Models

In the low-latitude Northwestern Pacific the North Equatorial Current terminates offshore of the Philippines and the Kuroshio and Mindanao Currents originate along the maritime western boundary. A fallow region between these western boundary currents marks the bifurcation whose position varies on seasonal and interannual scales. All well, remote time-varying oceanic signals generated in the interior Pacific basin by both wind stress and the intrinsic instability of the ocean circulation, propagate westwards into the boundary current region. Here we use two forced global fine resolution ocean general circulation models to advance understanding of the physical processes governing the origin and bifurcation of the two low latitude boundary currents. The models fully resolve mesoscale eddies in the region of interest and the atmospheric fluxes vary on synoptic and interannual time scales. We discuss the variability of the partitioning of flow into the two western boundary currents together with the bifurcation latitude on scales through interannual. Particularly we examine the coherence between sea surface height anomaly in the two currents at the northern and southern ends of the Philippines and that in the offshore region for, among others, the 100d and interannual bands. Strong coherence is found in the interannual band indicating planetary wave activity while for 100 days significant coherence occurs in two coastal bands that extend from the northern and southern tips of the Philippines to roughly the location of the bifurcation where they diverge offshore and are seen out to about 130°E. This coherence likely represents frontal instability activity and thus could provide a means of quantifying the origin of the two boundary currents.