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Formation process of the Kuroshio Large Meander in 2004

Norihisa Usui(1) , Hiroyuki Tsujino(1) , Yosuke Fujii(1) , and Masafumi Kamachi(1)

(1) Meteorological Research Institute, 1-1 Nagamine Tsukuba, 3050052, Japan

Abstract

The Kuroshio south of Japan exhibits remarkable bimodal features, namely, the large meander (LM) path and the non-large meander (NLM) path. In 2004 summer, a LM event ocurred for the first time in 13 years, and the LM path is maintained for about one year. We looked into the formation process of the LM event in 2004 using the MRI Multivariate Ocean Variational Estimation (MOVE) System, an ocean data assimilation system. Three-Dimensional Variational (3DVAR) method with vertical coupled temperature-salinity Empirical Orthogonal Function (EOF) modal decomposition is used in the MOVE-System. The western North Pacific model with a resolution of 0.1 degree (MRI.COM: MRI Community Ocean Model) is used for the dynamical model. The altimeter data (TOPEX/Poseidon, ERS-1/2, Jason-1, ENVISAT)and in-situ (ship and AGRO float) temperature and salinity data are assimilated. The assimilation results reproduced well the formation process of the Kuroshio large meander occurred in 2004 summer. In 2004 spring, a cold eddy corresponding to the small meander can be seen southeast of Kyushu, located south west of Japan. At the middle of May, a warm eddy located south of the cold eddy interacts with the cold eddy. As a result of the interaction, a deep anti-cyclonic eddy is induced between the warm and cold eddies, and propagates eastward along the Kuroshio path. At the middle of August, the small meander develops into the LM under this phase relation of upper and lower layer eddies. Thus, the formation process of the LM path can be understood as a growth of the baroclinic instability. The relation with the Kuroshio transport or the large scale field will also be presented.

 

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                 Last modified: 07.10.03