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Simulation of the Kuroshio using a primitive equation ocean model

 

Humio Mitsudera*1, Yasushi Yoshikawa*2, Bunmei Taguchi*3 and Hirohiko Nakamura*4

*1 International Pacific Research Center

*2 Japan Marine Science and Technology Center

*3 Mitsubishi Research Institute Inc.

*4 Dept. Fisheries, Kagoshima University

 

A simulation of the Kuroshio has been performed using a regional, primitive equation ocean model based on POM. The model includes realistic topography and coastline, a high resolution horizontal grid (1/8 degree on average), and 32 sigma levels. The model is forced by the inflow / outflow of the Kuroshio and the Oyashio, Hellerman and Rosenstein wind stress, and heat flux deduced from COADS.

Overall features of the Kuroshio flow are well represented in this model. In particular, the separation of the Kuroshio from the coast of the eastern edge of the Honshu Island is clearly represented. Meandering features of the Kuroshio and its extension are also well captured, where strong anticyclonic recirculation in the Shikoku basin and in the Kuroshio extension area, superimposed upon the Subtropical Mode Water circulation, are present. The recirculation in the extension area shows transport more than 100sv, which is comparable to that estimated recently along the WOCE P10 section.

In this paper the experiments with variable inflow / outflow of the Kuroshio are discussed. The model exhibits bimodality in Kuroshio paths off the coast of Japan, which are the straight and the meandering ones. There is a tendency to take the large meander when the inflow transport from the south is large. In the meandering cases the anticyclonic recirculation off the Shikoku is strong, which is likely to play an active role in the formation and maintenance of the large meander. The most striking is the fact that barotropic potential vorticity in the anticyclonic recirculation off Shikoku is well homogenized when the path shows a meandering state; it leads to even stronger recirculation with relatively weak forcing such as that due to eddies. Quasi-steady experiments with slow increase and decrease of the inflow show (quasi) multiple equilibrium states in the Kuroshio paths in a certain range of the inflow transport.

 

 

 

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