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In the Indo‐Australian basin the strongest intraseasonal variability occurs during the second half of the year according to satellite altimeter data. This study attempts to identify the generation mechanism of this variability by means of numerical ocean modeling. By separately varying winds and transports through individual straits it is shown that the seasonal cycles of both the wind and the transport through the Lombok Strait play crucial roles in generating mixed barotropic and baroclinic instabilities during July–September. Both the spatial and temporal patterns of the variability are also sensitive to transports through the Ombai Strait and the Timor Passage, though to a lesser degree. The Smagorinsky scheme in the model is essential for these instabilities to reach the observed magnitude of standard deviation in sea level anomaly; constant eddy viscosity, which needs to be sufficiently large for the Somali Current in summer, would damp the eddies in the Indo‐Australian basin severely.

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Precipitation is one of the main forcings for sea surface salinity (SSS). The accuracy of precipitation products over open oceans, however, remains a problem due to the lack of in situ measurements. In this study, we use an ocean model to test the performance of precipitation products in the Indian Ocean, where large salinity contrasts exist. The model consists of four active layers overlying a deep, inert ocean, the top‐most layer being a mixed layer governed by Kraus‐Turner physics. Solutions are forced by monthly‐mean precipitation climatologies, and their surface salinity fields (S1) are compared with observed SSS. In the Indian Ocean, both river runoff and the Indonesian throughflow significantly influence the long‐term mean SSS distribution, and hence adequate treatment of these boundary forcings is a prerequisite for the model to be useful as a tool for evaluating precipitation products. We also explored the sensitivity of solutions to various model parameters and forcing, making sure they are not the main source of the bias. The model produces the best annual‐mean S1 field when it is forced by the Climate Prediction Center Merged Analysis of Precipitation (CMAP) product, a merged precipitation product based on rain‐gauge data and several satellite estimates. An amplitude adjustment of the Global Precipitation Climatology Project (GPCP) product is suggested by the model S1, supporting the notion that merged products give reliable spatial patterns but not necessarily correct magnitudes. Problems with some other precipitation products are also discussed, in terms of their potential distortion of mixed‐layer thickness.

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.

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.