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Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation

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Abstract

We describe an operational ocean data assimilation system for the Kuroshio and its validation using a nine-year reanalysis (historical run from 1993 to 2001) dataset of upper-ocean state estimation in the North Pacific. The horizontal structure of volume transport of the Ryukyu Current System (RCS) is shown from the reanalysis: The RCS is connected to the flow of the subtropical gyre, and its volume transport gradually increases from south-east of Okinawa (5–10 Sv) to the east of Amami-Ohshima Island (20 Sv). Comparing the reanalysis with independent observations on the southeast slope of the Amami-Ohshima Island indicates that the root mean square differences (RMSDs) are 0.076 (0.037) m/s in the period of December 1998 to November 1999 (November 1999 to November 2000) respectively. The reanalysis field has a bias (3.1 Sv) of the volume transport of the RCS and the RMSD (3.5 Sv) which is larger than the observed variability (2.81 Sv). Surface velocity and the Kuroshio axis south of Japan are also examined. Comparison of the reanalysis and ADCP data gave maximum RMSD of 0.749 (0.271) m/s in the strong (weak) current regions, respectively. The annual mean value of the axis error is 19 km in 1998. The RMSD of the error is at most 50 km, in 294 cases in the observation period, which is smaller than the observed root mean square variability of the axis (64 km).

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Authors and Affiliations

  1. Meteorological Research Institute, Nagamine, Tsukuba, 305-0052, Japan

    Masafumi Kamachi

  2. Office of Marine Prediction, Japan Meteorological Agency, Ohtemachi, Tokyo, 100-8122, Japan

    Tsurane Kuragano, Satoshi Sugimoto, Kumi Yoshita & Toshiyuki Sakurai

  3. Faculty of Fisheries, Kagoshima University, Shimoarata, Kagoshima, 890-0056, Japan

    Hiroshi Ichikawa, Hirohiko Nakamura & Ayako Nishina

  4. Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Science, Kyushu University, Kasuga, Fukuoka, 816-8580, Japan

    Atsuhiko Isobe & Daisuke Ambe

  5. Faculty of Engineering, Hiroshima University, Kagamiyama, Higashi-Hiroshima, 739-8527, Japan

    Masazumi Arai & Noriaki Gohda

  6. LEGOS/BRESM, 14, Av. Edouard Belin, 31400, Toulouse, France

    Francesco Uboldi

Authors
  1. Masafumi Kamachi
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  2. Tsurane Kuragano
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  3. Hiroshi Ichikawa
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  4. Hirohiko Nakamura
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  5. Ayako Nishina
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  6. Atsuhiko Isobe
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  7. Daisuke Ambe
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  8. Masazumi Arai
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  9. Noriaki Gohda
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  10. Satoshi Sugimoto
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  11. Kumi Yoshita
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  12. Toshiyuki Sakurai
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  13. Francesco Uboldi
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Kamachi, M., Kuragano, T., Ichikawa, H. et al. Operational Data Assimilation System for the Kuroshio South of Japan: Reanalysis and Validation. Journal of Oceanography 60, 303–312 (2004). https://doi.org/10.1023/B:JOCE.0000038336.87717.b7

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  • DOI: https://doi.org/10.1023/B:JOCE.0000038336.87717.b7

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