Newsletter No.5 January-1999@

Dr.Fumihiko Mitsudera
ccording to recent research,there are profound signals of climate variations of decadal to interdecadal time scale in the North Pacific region.Understanding of their mechanism,through what feedback the climate variations occur,is a current hot topic.
    I am very interested in how strong currents and jets,such as the Kuroshio and the subarctic front,play a role in the feedback system of the climate variations.These strong currents produce meanders and mesoscale eddies through shear instability.These eddies then cause mixing of potential vorticity,which further causes mean recirculation flows adjacent to the currents.The circulation of the Subtropical Mode Water in the southern side of the Kuroshio extension is thought to occur in this manner.Moreover,there exists a similar westward flow in the northern side of the Kuroshio extension,discovered recently by surface drifter observation.It is well known that the ocean release tremendous heat to the atmosphere in the western Pacific where the Kuroshio exists.Therefore,redistribution of heat in this area can give strong impact on the air-sea interaction there.Satellite data analysis deduced that more than 30%of the heat budget can be attributed to eddy induced flows.

    I am proceeding a research of these phenomena using high resolution ocean models.According to the numerical-experiment results of a regional ocean model near Japan,I have found that intense recirculation may form off the south coast of Japan due to homogenization of potential vorticity there,leading to the enhancement of the Kuroshio large meander.The Kuroshio extension area is not fully analysed yet,but we can clearly see that the warm water advected from subtropical area spreads into the Subtropical Mode Water through eddy processes.

    Joint international observation of the Kuroshio extension area is planned from the year 2000 to 2003.This project aims at understanding the dynamics in the Kuroshio extension and the air-sea interaction,combining new observation technology,such as acoustic tomography,Triton buoys,subsurface floats,inverted echo sounders,with state-of-art modeling works conducted in the IGCR and IPRC.This further aims at improving parameterization for climate models.We also expect the results will be applied,not only to the climate prediction,but also to the variety of fields such as fishery and maritime navigation.

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