TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 60 (No. 2), pp. 321-328, 2004

Seasonality of the Kuroshio Transport Revealed in a Kuroshio Assimilation System

Atsuhiko Isobe1*, Masafumi Kamachi2, Yukio Masumoto3, Hiroshi Uchida4 and Tsurane Kuragano2

1Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
2Oceanographic Research Department, Meteorological Research Institute, Nagamine, Tsukuba 305-0052, Japan
3Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan; also at Frontier Research System for Global Change, Showa, Kanazawa-ku, Yokohama 236-0001, Japan
4Japan Marine Science and Technology Center, Ocean Observation and Research Department, Natsushima, Yokosuka 237-0061, Japan

(Received 30 April 2003; in revised form 30 October 2003; accepted 30 October 2003)

Abstract: The seasonal variation of the Kuroshio transport south of Japan has been investigated using the results of an assimilation model. Annual and semiannual variations of the transport and dynamic depth anomaly are reconstructed by CEOF (complex orthogonal empirical function) analysis. In the basin west of the Izu-Ogasawara Ridge, the annual component of the variation propagates westward with the phase speed of the long Rossby wave associated with the first baroclinic mode. The variation also shows a similar tendency to that reproduced in a wind-driven, two-layer model with a ridge. This suggests that the annual variation revealed in the assimilation model is associated with the baroclinic first mode of motion excited above the Izu-Ogasawara Ridge. Furthermore, it is found that both the semiannual component and the annual component are important members determining the seasonal variation of the Kuroshio transport south of Japan. The semiannual component is revealed as a double gyre pattern in the basin west of the Izu-Ogasawara Ridge.

*Corresponding author E-mail: isobe@esst.kyushu-u.ac.jp

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