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Abstract

Most of discussions on the seasonal evolution and its interannual variability of the Java upwelling system are based on the surface variables observed by satellite remote sensing. Better understanding of physical mechanisms responsible for these variations requires detailed investigation on subsurface structures of the upwelling system. This study revisits the seasonal development of the upwelling system, focusing on subsurface temperature and velocity structures during boreal summer, using the previously observed data and outputs from a high-resolution ocean GCM. Results suggest that the upwelling off the coast of Java consists of two kinds of upwelling: a typical coastal upwelling due to alongshore winds and offshore upwelling associated with wind stress curl. The offshore upwelling first appear in the eastern region near the Lombok Strait in June, then it expands to the west with the progression speed of about 0.18 m/s, which is consistent with the phase speed of second baroclinic Rossby wave at this latitude. The upwelling favorable alongshore winds strengthen in the western region near Sumatra Island in July/August, while the surface upwelling signal has its maximum always in the eastern region off Java Island. Combination of these two upwelling processes is responsible for the seasonal evolution of the upwelling system off the southern coast of Java Island.