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).
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
Ambe, D., S. Imawaki, S. Uchida and K. Ichikawa (2004): Estimating the Kuroshio axis south of Japan using combination of satellite altimetry and drifting buoys. J. Oceanogr., 60, this issue, 375–382.
Bennett, A. F. (2002): Inverse Modeling of the Ocean and Atmosphere. Cambridge University Press, Cambridge, 234 pp.
Bourtier, F. and P. Courtier (1999): Data assimilation concepts and methods. Rep. of ECMWF, 75 pp.
Bryan, K. (1969): A numerical method for the study of the world ocean. J. Comp. Phys., 4, 347–376.
Hellerman, S. and M. Rosenstein (1983): Normal monthly wind stress over the world ocean with error estimates. J. Phys. Oceanogr., 13, 1093–1104.
Ichikawa, H., H. Nakamura, A. Nishina and M. Higashi (2004): Variability of northeastward current southeast of northern Ryukyu Islands. J. Oceanogr., 60, this issue, 351–363.
Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, S. Umatani and The ASUKA Group (2001): Satellite altimeter monitoring the Kuroshio transport south of Japan. Geophys. Res. Lett., 28, 17–20.
Ishizaki, H. and T. Motoi (1999): Reevaluation of the Takano-Oonishi scheme for momentum advection on bottom relief in ocean models. J. Atmos. Ocean. Tech., 16, 1994–2010.
Isobe, A., M. Kamachi, Y. Masumoto, H. Uchida and T. Kuragano (2004): Seasonality of the Kuroshio transport revealed in a Kuroshio assimilation system. J. Oceanogr., 60, this issue, 321–328.
Kalnay, E. (2003): Atmospheric Modeling, Data Assimilation and Predictability. Cambridge University Press, Cambridge, 341 pp.
Kalnay, E. and Coauthors (1996): The NCEP/NCAR 40-year reanalysis progect. Bull. Amer. Meteor. Soc., 77, 434–471.
Kamachi, M., T. Kuragano, N. Yoshioka, J. Zhu and F. Uboldi (2001): Assimilation of satellite altimetry into a Western North Pacific operational model. Adv. In Atmos. Sci., 18, 767–786.
Kamachi, M., T. Kuragano and S. Sugimoto (2003): Present status of assessments of ocean data assimilation products: An introduction to GODAE metrics. Weather Service Bulletin, JMA, 70, S107–S122 (in Japanese).
Kamachi, M., T. Kuragano, S. Sugimoto, K. Yoshita, T. Sakurai, T. Nakano, N. Usui and F. Uboldi (2004): Short-range prediction experiments with operational data assimilation system for the Kuroshio south of Japan. J. Oceanogr., 60, this issue, 269–282.
Kaneko, A., Z. Yuan, N. Gohda, M. Arai, H. Nakajima, H. Zheng and T. Sugimoto (2001): Repeat meridional survey of the western North Pacific subtropical gyre by a VOS ADCP during 1997 to 1998. Geophys. Res. Lett., 28, 3429–3434.
Kawabe, M. (1980): Sea level variations around the Nansei Islands and the large meander in the Kuroshio south of central Japan. J. Oceanogr. Soc. Japan, 36, 227–235.
Killworth, P. D. (1996): Time interpolation of forcing fields in ocean models. J. Phys. Oceanogr., 26, 136–143.
Kimura, Y. and M. Endoh (1989): Response experiment of the Pacific Ocean to anomalous wind stress with ocean general circulation model. Tech. Rep. of the Met. Res. Inst., 24, 96 pp.
Kuragano, T. and M. Kamachi (2000): The global statistical space-time scales of oceanic variability estimated from the TOPEX/POSEIDON altimeter. J. Geophys. Res., 105, 955–974.
Kuragano, T. and M. Kamachi (2003): Altimeter's capability of reconstructing realistic eddy fields using space-time optimum interpolation. J. Oceanogr., 59, 765–781.
Kuragano, T. and M. Kamachi (2004): Balance of volume transports between horizontal circulation and meridional overturn in the North Pacific subarctic region. J. Oceanogr., 60, this issue, 439–451.
Kuragano, T., S. Sugimoto, N. Yoshioka, T. Yoshida and M. Kamachi (2001): Objective analysis of temperature and salinity with satellite altimetry and in situ observation in the Pacific. Weather Service Bulletin, JMA, 68, 99–119 (in Japanese).
Levitus, S. (1982): Climatological atlas of the world ocean. NOAA Prof. Paper, 13, 174 pp.
Levitus, S. and T. P. Boyer (1994): World Ocean Atlas 1994, Vol. 4: Temperature, NOAA Atlas NESDIS 4, 117 pp.
Levitus, S., R. Gurgett and T. P. Boyer (1994): World Ocean Atlas 1994, Vol. 3: Salinity, NOAA Atlas NESDIS 3, 99 pp.
Nitani, H. (1972): Chapter 5, Beginning of the Kuroshio. p. 120–163. In Kuroshio, Its Physical Aspects, ed. by H. Stommel and K. Yoshida, Washington Univ. Press.
Richardson, L. F. and H. Stommel (1948): Note on eddy diffusion in the sea. J. Meteorol., 5, 238–240.
Saiki, M. (1982): Relation between the geostrophic flux of the Kuroshio in the Eastern China Sea and its large-meanders in south of Japan. Oceanogr. Mag., 32, 11–18.
Stommel, H. (1949): Horizontal diffusion due to oceanic turbulence. J. Mar. Res., 8, 199–225.
Sugimoto, S., M. Kamachi, K. Yoshita, K. Murakami, S. Kawae, Y. Miura, M. Tani, N. Yoshioka, S. Minato, N. Miyagi, T. Segawa and K. Okano (2003): Validation of the ocean comprehensive analysis system. Weather Service Bulletin, JMA, 70, S71–S105 (in Japanese).
Uboldi, F. (1998): Report on Eddy Synthetic Models, Reports in COMPASS Group No. 2, Met. Res. Inst., 49 pp.
Wunsch, C. (1996): The Ocean Circulation Inverse Problem. Cambridge University Press, Cambridge, 442 pp.
Yoon, J.-H. (2003): Pacific circulation model. Proceedings of the Annual Report of the Research Revolution 2002 (RR2002), MEXT, Tokyo, 119–120.
Zhu, J. and M. Kamachi (2000): An adaptive variational method for data assimilation with imperfect models. Tellus, 52A, 265–279.
Zhu, X.-H., I.-S. Han, J.-H. Park, H. Ichikawa, K. Murakami, A. Kaneko and A. Ostrovskii (2003): The northeastward current southeast of Okinawa Island observed during November 2000 to August 2001. Geophys. Res. Lett., 30, No. 2, 1071, doi:10.1029/2002GL015867.
About this article
Cite this article
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
- Data assimilation
- Ryukyu Current System