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The Leeuwin Current System (LCS) along the coast of Western Australia consists of the poleward-flowing Leeuwin Current (LC), the equatorward-flowing Leeuwin Undercurrent (LUC), and neighboring flows in the south Indian Ocean (SIO). Using geostrophic currents obtained from a highly resolved ( 1 /88) hydrographic climatology [CSIRO Atlas of Regional Seas (CARS)], this study describes the spatial structure and annual variability of the LC, LUC, and SIO zonal currents, estimates their transports, and identifies linkages among them. In CARS, the LC is supplied partly by water from the tropics (an annual mean of 0.3 Sv; 1 Sv [ 10 6 m 3 s 21 ) but mostly by shallow (&200 m) eastward flows in the SIO (4.7 Sv), and it loses water by downwelling across the bottom of this layer (3.4 Sv). The downwelling is so strong that, despite the large SIO inflow, the horizontal transport of the LC does not much increase to the south (from 0.3 Sv at 228S to 1.5 Sv at 348S). This LC transport is significantly smaller than previously reported. The LUC is supplied by water from south of Australia (0.2 Sv), by eastward inflow from the SIO south of 288S (1.6 Sv), and by the downwelling from the LC (1.6 Sv) and in response strengthens northward, reaching a maximum near 288S (3.4 Sv). North of 288S it loses water by outflow into subsurface westward flow (23.6 Sv between 288 and 228S) and despite an additional downwelling from the LC (1.9 Sv), it decreases to the north (1.7 Sv at 228S). The seasonality of the LUC is described for the first time.

The Tsuchiya jets (TJs) are narrow eastward currents, located a few degrees on either side of the equator at depths from 200 to 500 m in the Pacific Ocean. In this study, non-eddy-resolving, oceanic general circulation models (OGCMs) are used to investigate the dynamics of the southern TJ. Most solutions are found in a rectangular basin extending 100°zonally and from 40°S to 10°N. They are forced by idealized zonal and meridional winds representing the trades and the southerly winds near the South American coast, by a prescribed interocean circulation (IOC) that enters the basin through the southern boundary and exits through the western boundary from 2°to 6°N (the model's Indonesian passages), and by surface heating that warms the ocean in the Tropics. A suite of solutions is presented to isolate effects of each forcing and mixing process. A few solutions are also found to a global OGCM driven by realistic forcings. Solutions forced by all of the aforementioned processes and with minimal diffusion resemble the observed flow field in the tropical South Pacific. A narrow eastward current, the model southern TJ, flows across the basin along the southern edge of a thick equatorial thermostad, and upwells at the eastern boundary. Its deeper part is supplied by water that leaves the western boundary current somewhat south of the equator. Its shallower part originates from water that diverges from the deep portion of the Equatorial Undercurrent (EUC); as a result, the TJ transport increases to the east and the TJ warms as it flows across the basin. A major part of the water that upwells at the eastern boundary is supplied by the TJ with a minor contribution from the southern boundary region. In idealized-basin solutions without forcing either by the IOC or meridional wind, the TJ is weak or absent. These, and other, properties suggest that the dynamics of the model's TJ are those of an arrested front, which in a 2 1 ⁄2-layer model are generated when characteristics of the flow merge or intersect. When diffusivity is increased to commonly used values, the thermostad is less well defined or even absent and the TJ is weak, suggesting that excessive diffusion is the reason why TJs are not present in many previous OGCMs. In the solution to a global OGCM, the southern TJ still exists without the IOC, although it is warmed by 1°C, indicating that much of its water is supplied by an overturning cell confined within the Pacific basin.

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The South China Sea throughflow begins at the Luzon Strait, as an intrusion of the Kuroshio. At the present time, there are insufficient in situ measurements either to estimate accurately the transport loss or to provide a clear picture of the Kuroshio pathway at the Luzon Strait. In this study, we use newly available, multi‐year, high‐resolution satellite images and a numerical model to track the warm, relatively low‐biomass, Pacific water carried by the Kuroshio. A suite of numerical experiments are carried out to identify key factors that influence Kuroshio paths at the Luzon Strait. The model can reproduce the satellite‐inferred Kuroshio paths across the Luzon Strait only when a significant amount of the Kuroshio water is allowed to enter the Luzon Strait during December–February, therefore providing strong evidence for the existence of the South China Sea throughflow.

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The salinity distribution in the South China Sea (SCS) has a pronounced subsurface maximum from 150–220 m throughout the year. This feature can only be maintained by the existence of a mean flow through the SCS, consisting of a net inflow of salty North Pacific tropical water through the Luzon Strait and outflow through the Mindoro, Karimata, and Taiwan Straits. Using an inverse modeling approach, the authors show that the magnitude and space–time variations of the SCS thermohaline structure, particularly for the salinity maximum, allow a quantitative estimate of the SCS throughflow and its distribution among the three outflow straits. Results from the inversion are compared with available observations and output from a 50-yr simulation of a highly resolved ocean general circulation model. The annual-mean Luzon Strait transport is found to be 2.4 ± 0.6 Sv (Sv ≡ 106 m3 s−1). This inflow is balanced by the outflows from the Karimata (0.3 ± 0.5 Sv), Mindoro (1.5 ± 0.4), and Taiwan (0.6 ± 0.5 Sv) Straits. Results of the inversion suggest that the Karimata transport tends to be overestimated in numerical models. The Mindoro Strait provides the only passage from the SCS deeper than 100 m, and half of the SCS throughflow (1.2 ± 0.3 Sv) exits the basin below 100 m in the Mindoro Strait, a result that is consistent with a climatological run of a 0.1° global ocean general circulation model.