Journal of Oceanography

, Volume 60, Issue 2, pp 303–312 | Cite as

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

  • Masafumi Kamachi
  • Tsurane Kuragano
  • Hiroshi Ichikawa
  • Hirohiko Nakamura
  • Ayako Nishina
  • Atsuhiko Isobe
  • Daisuke Ambe
  • Masazumi Arai
  • Noriaki Gohda
  • Satoshi Sugimoto
  • Kumi Yoshita
  • Toshiyuki Sakurai
  • Francesco Uboldi

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).

Data assimilation Kuroshio reanalysis Ryukyu Current System 

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Copyright information

© The Oceanographic Society of Japan 2004

Authors and Affiliations

  • Masafumi Kamachi
    • 1
  • Tsurane Kuragano
    • 2
  • Hiroshi Ichikawa
    • 3
  • Hirohiko Nakamura
    • 3
  • Ayako Nishina
    • 3
  • Atsuhiko Isobe
    • 4
  • Daisuke Ambe
    • 4
  • Masazumi Arai
    • 5
  • Noriaki Gohda
    • 5
  • Satoshi Sugimoto
    • 2
  • Kumi Yoshita
    • 2
  • Toshiyuki Sakurai
    • 2
  • Francesco Uboldi
    • 6
  1. 1.Meteorological Research InstituteTsukubaJapan
  2. 2.Office of Marine PredictionJapan Meteorological AgencyTokyoJapan
  3. 3.Faculty of FisheriesKagoshima UniversityKagoshimaJapan
  4. 4.Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering ScienceKyushu UniversityFukuokaJapan
  5. 5.Faculty of EngineeringHiroshima UniversityHigashi-HiroshimaJapan
  6. 6.LEGOS/BRESMToulouseFrance

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