Basic Research on Development of Ocan Prediction Models for Asian Marginal Seas

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The present basic research for developing ocean forecasting models has been conducted jointly by oceanographers of Tokyo Univ., Kyoto Univ., Kyushu Univ., Mie Univ., and Ehime Univ. with a particular Emphasis on the NEAR GOOS region. The major achievements are described in the following.We have developed an ultra high-resolution nested ocean model (with horizontal resolution of 1/18 degree) and have successfully simulated the vertical structure and the path of the Kuroshio. The model also resolves the ocean tide. Analyzing the model results, we have clarified the important role of JEBAR (joint effect of baroclinicity and bottom relief) in steering the Kuroshio eastward in the region southwest of the Kyushu Island ; the role of the bottom torque is to drive the Kuroshio into the deeper region. Tracer experiments show that about 50% (20%) of the water mass of the Tsushima Current is from the Taiwan Strait and another 50% (70%) is from the Kuroshio in summer (winter).The outflow of the Okhotsk Sea water of low potential vorticity is one of origins of the North Pacific Intermediate Water. Using a high-resolution non-hydrostatic ocean model, we have shown that eddy shedding due to the baroclinic instability of the front formed by tidal mixing plays a crucial role in this process. The water left from the Okhotsk Sea penetrates even into the Shikoku Basin.The RIAMMOM ocean model is successfully used for hindcasting experiments of currents in the Japan Sea. The data assimilation method used in the experimens is based on the Kalman filter. We have demonstrated that the ocean forecasting limit is about two months. We have also shown that to resolve downwelling associated with baroclinic instability as well as convection along the ocean front is a necessary ingredient to simulate realistical ly subsurface and intermediate conditions in the Japan Sea.