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2004 Fiscal Year Final Research Report Summary

Improved estimates of heat and water mass transports in the Pacific Ocean by a long-term data assimilation experiment using a 4-dimensional variational approach

Research Project

Project/Area Number 14340141
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section一般
Research Field Meteorology/Physical oceanography/Hydrology
Research InstitutionKYOTO UNIVERSITY

Principal Investigator

AWAJI Toshiyuki  Kyoto University, Dept.of Geophysics, Professor, 大学院・理学研究科, 教授 (40159512)

Co-Investigator(Kenkyū-buntansha) KONDA Masanori  Kyoto University, Dept.of Geophysics, Assistant Professor, 大学院・理学研究科, 助手 (10273434)
ISHIKAWA Yoichi  Kyoto University, Dept.of Geophysics, Assistant Professor, 大学院・理学研究科, 助手 (70335298)
FUKAZAWA Masao  JAMSTEC, IORGC, Program Director, 地球環境観測研究センター, プログラムディレクター (10143546)
Project Period (FY) 2002 – 2004
Keywords4-dimensional variational ocean data assimilation / Heat and water mass transports / State estimation / Variability and predictability
Research Abstract

The main objective of our research is to construct an innovative 4-dimensional variational(4D-VAR) data assimilation system capable of providing high-quality comprehensive datasets. Synthesis of observational data and state-of-the-art general circulation models by the variational approach has the ability to produce a dynamically self-consistent space-time dataset. Such datasets are urgently required for more accurate prediction and for better estimation of the dynamical state of the Pacific Ocean associated with global warming.
In order to achieve our goal, we have successfully constructed a 4D-VAR data assimilation system on a parallel computer machine, and have applied it to a long-term reanalysis experiment during the period after the late 1980's. This experiment assimilated all the observational data available into an ocean general circulation model. The obtained reanalysis dataset shows good consistency with previous knowledge of important climate events. For example, the evolution … More of Nino3 SST is well reproduced (its error value reduces to about 1/2 of that from the earlier simulations), which supports the notion that our dataset accurately represents the climate variability in this region. Further, our reanalysis dataset exhibits realistic subsurface water mass distribution and enables us to clarify the water mass formation and movement processes. An application of a sensitivity experiment to the dichothermal and mesothermal water pathways that characterize the northwest North Pacific circulation is performed in which we investigate the sensitivity to an artificial cost given in the subarctic Pacific region. The distribution of adjoint variables shows good consistency with previous studies of the subtropical Kuroshio Extension region and western subarctic region. Similarly, intermediate waters can be traced back to their source regions. Using our reanalysis data set, we estimated meridional heat and water mass transports associated with the overturn in the Pacific Ocean. A close look at the meridional distributions reveal that the annual mean and the seasonal change are by and large consistent with previous knowledge. These results confirm that our 4D-VAR data assimilation system is a powerful tool for the understanding and prediction of the dynamical state of the Pacific Ocean. Less

  • Research Products

    (12 results)

All 2005 2004 2003

All Journal Article (12 results)

  • [Journal Article] Effects of tidal mixing at the Kuril Straits on the North Pacific ventilation : Part 1. Freshening and dynamical adjustment of intermediate layers revealed from numerical experiments.2005

    • Author(s)
      Nakamura T., T.Toyoda, Y.Ishikawa, T.Awaji
    • Journal Title

      J.Geophys.Res. (発表予定)(accepted)

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Effects of tidal mixing at the Kuril Straits on the North Pacific ventilation : Part 1. Freshening and dynamical adjustment of intermediate layers revealed from numerical experiments.2005

    • Author(s)
      Nakamura T., T.Toyoda, Y.Ishikawa, T.Awaji
    • Journal Title

      J.Geophys.Res. (accepted)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Preconditioning of winter mixed layer in the formation of North Pacific eastern subtropical mode water.2004

    • Author(s)
      Toyoda, T., T.Awaji, Y.Ishikawa, T.Nakamura
    • Journal Title

      Geophys.Res.Lett.31

      Pages: doi:10.1029/2004GL020677

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Tidal mixing in the Kuril Straits and its impact on the ventilation in the North Pacific Ocean.2004

    • Author(s)
      Nakamura, T., T.Toyoda, Y.Ishikawa, T.Awaji
    • Journal Title

      J.Oceanogr 60

      Pages: 411-423

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Application of sensitivity analysis using an adjoint model for short-range forecast of the Kuroshio path south of Japan.2004

    • Author(s)
      Ishikawa, Y., T.Awaji, N.Komori, T.Toyoda
    • Journal Title

      J.Oceanogr 60

      Pages: 293-301

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Preconditioning of winter mixed layer in the formation of North Pacific eastern subtropical mode water.2004

    • Author(s)
      Toyoda, T., T.Awaji, Y.Ishikawa, T.Nakamura
    • Journal Title

      Geophys.Res.Lett. 31

      Pages: doi:10.1029/2004GL020677

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Tidal mixing in the Kuril Straits and its impact on the ventilation in the North Pacific Ocean.2004

    • Author(s)
      Nakamura, T., T.Toyoda, Y.Ishikawa, T.Awaji
    • Journal Title

      J.Oceanogr. 60

      Pages: 411-423

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Application of sensitivity analysis using an adjoin model for short-range forecast of the Kuroshio path south of Japan.2004

    • Author(s)
      Ishikawa, Y., T.Awaji, N.Komori, T.Toyoda
    • Journal Title

      J.Oceanogr. 60

      Pages: 293-301

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] State estimation of the North Pacific Ocean by a four-dimensional variational data assimilation experiment2003

    • Author(s)
      Awaji, T., S.Masuda, Y.Ishikawa, N.Sugiura, T.Toyoda, T.Nakamura
    • Journal Title

      J.Oceanogr 59

      Pages: 931-943

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] Improved estimates of the dynamical state of the North Pacific Ocean from a 4-dimensional variational data assimilation.2003

    • Author(s)
      Masuda, S., T.Awaji, N.Sugiura, Y.Ishikawa, K.Baba, K.Hirouci, N.Komori
    • Journal Title

      Geophys.Res.Lett. 30

      Pages: doi:10.1029/2003GRL017604

    • Description
      「研究成果報告書概要(和文)」より
  • [Journal Article] State estimation of the North Pacific Ocean by a four-dimensional variational data assimilation experiment.2003

    • Author(s)
      Awaji, T., S.Masuda, Y.Ishikawa, N.Sugiura, T.Toyoda, T.Nakamura
    • Journal Title

      J.Oceanogr. 59

      Pages: 931-943

    • Description
      「研究成果報告書概要(欧文)」より
  • [Journal Article] Improved estimates of the dynamical state of the North Pacific Ocean from a 4-dimensional variational data assimilation.2003

    • Author(s)
      Masuda, S., T.Awaji, N.Sugiura, Y.Ishikawa, K.Baba, K.Horiuchi, N.Komori
    • Journal Title

      Geophys.Res.Lett. 30

      Pages: doi:10.1029/2003GRL017604

    • Description
      「研究成果報告書概要(欧文)」より

URL: 

Published: 2006-07-11  

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