Variability of Western Boundary Currents

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Ocean general circulation models have been improved dramatically in recent years ; we are now able to compare directly results from models with in situ observations. In the present study we have accelerated this movement in close cooperation with international colleagues who show strong interests in the western boundary currents in the western Pacific. Our final goal is to provide high-resolution ocean models for practical purposes such as daily ocean current prediction. On the basis of last two-years' international cooperative research, we have been successful in achieving several important scientific findings as well as improvement of ocean models. First, we have demonstrated the role of the joint effect of baroclinicity and bottom relief on the Kuroshio transport variations. Secondly, we have discovered and named <the Luzon Undercurrent> both in models and in situ observations obtained during US-PRC WOCE cruises. Thirdly, we have studied in full depth the seasonal variations of the Indonesian Throughflow and published a special issue of J.Geophys.Res. We have distributed 50 reprint volumes all over the world. Fourthly, we have analyzed Russian data for the formation of lenses composed of the intermediate water. Fifthly, based on the model results, we have found the Sri Lanka Dome and Bay of Bengal Dome in the Indian Ocean and confirmed the existence by the new Levitus data as well as the TOPEX/POSEIDON satellite altimetry data. In addition, we have checked the model performance by comparing surface drifter data and model variability particulary for synoptic scale phenomena of the Kuroshio. It has turned out that the model variability is still weaker than reality. Therefore, it is necessary to introduce further high-resolution models with improved sub-grid scale parameterization. We are planning to do this on the basis of the present accomplishment.