Mean Structure and Variability of the Kuroshio from Northeastern Taiwan to Southwestern JapanABSTRACT. In the subtropical western North Pacific Ocean, the Kuroshio delivers heat, salt, and momentum poleward, much like its North Atlantic analog, the Gulf Stream. Though the Kuroshio generally flows along the western boundary from Taiwan to southeastern Japan as an "attached" current, the Kuroshio's strength, vertical structure, and horizontal position undergo significant temporal and spatial variability along this entire route. Ubiquitous mesoscale eddies and complicated topography associated with a string of marginal seas combine to make the western North Pacific a region with complex circulation. Here, we synthesize results from the recent US Origins of the Kuroshio and Mindanao Currents and Taiwan Observations of Kuroshio Transport Variability observational programs with previous findings to build a comprehensive picture of the Kuroshio on its route from northeastern Taiwan to southeastern Japan, where the current finally transitions from a western boundary current into the Kuroshio Extension, a vigorously meandering free jet. in the western North Pacific over the past decades, many of them supported by ONR, that have focused on different sections along the Kuroshio (Table 1). Here, we summarize some of these earlier field programs and synthesize them with OKMC/OKTV results to describe the downstream evolution of the Kuroshio along its route from the western Philippine Basin through the East China Sea to south of Japan (Figure 1a).
MEASURING THE KUROSHIODue to the rich eddy field in the western North Pacific (Figure 2a), individual synoptic sections across the Kuroshio from shipboard measurements are often not representative of the current's mean state. Longer duration measurements (or many crossings) are needed to estimate the current's mean transport and velocity structure. Since 1991, arrays of inverted echo sounders (IESs) have been deployed at various sections across the Kuroshio (e.g., Table 1 and the green lines in Figure 3a) to measure variability at hourly resolution for durations of one year or more. In most cases, the IESs were also equipped with pressure sensors (PIESs) and additional current sensors (CPIESs) or horizontal electric field sensors (HPIESs) to help establish the Kuroshio's time-varying position, absolute geostrophic transport, and velocity structure (see Meinen et al., 2002;Donohue et al., 2010;and Szuts, 2012, for reviews of the methodologies and the title page photo [opposite] for an image of a PIES). One of these experiments was along the Affiliated Surveys of the Kuroshio off Cape Ashizuri (ASUKA) Line, which extends 1,000 km southeastward from Shikoku, Japan, into the Philippine Basin (Figure 3a). A full array of instruments was deployed there from 1993 to 1995 (Book et al., 2002) with a reduced two-IES array maintained through (Kakinoki et al., 2008. Two IES arrays were also deployed along the PN Line, a repeat hydrographic line in the East China Sea northwest of Okinawa (labele...