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2003 Fiscal Year Final Research Report Summary

Studies on the Interaction between North Pacific Intermediate Water and the Kuroshio

Research Project

Project/Area Number 13440139
Research Category

Grant-in-Aid for Scientific Research (B)

Allocation TypeSingle-year Grants
Section一般
Research Field Meteorology/Physical oceanography/Hydrology
Research InstitutionThe University of Tokyo

Principal Investigator

YASUDA Ichiro  The University of Tokyo, Graduate School of Science, Associate Professor, 大学院・理学系研究科, 助教授 (80270792)

Co-Investigator(Kenkyū-buntansha) WATANABE Tomowo  Fisheries Research Agency, Marine Productivity Division, Head of the Laboratory, 中央水産研究所・海洋生産部, 室長(研究職)
HIBIYA Toshiyuki  The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (80192714)
Project Period (FY) 2001 – 2003
KeywordsKuroshio / Kuroshio Extension / Oyashio / ocean current / water mass / physical oceanography / oceanography / air-sea interaction
Research Abstract

We here hypothesize that variation of the cross-gyre transport from the subarctic to subtropical gyres producing NPIW induces long-term variations in the Kuroshio/Kuroshio Extension current system. In order to validate this hypothesis and detect the actually occurring formation processes of NPIW, we conducted data-analysis, numerical experiments and field observations; we successfully obtained extraordinary results. (1) Based on four surveys of water masses and ocean currents using CTD/LADCP observation, we revealed about 10Sv of cross-gyre Oyashio transport through the following two processes : direct cross-gyre transport along the western boundary and cross-subarctic front (SAF) process occurring along the offshore SAF due to isopycnal mixing. (2) The intrusion of western boundary currents across the wind-driven gyre boundary and related cross-gyre transport are realistically reproduced with a eddy-permitting three layer numerical models with realistic topography and annual mean wind … More stress, with special emphasis on the Oyashio southward intrusion and North Pacific intermediate Water (NPIW) formation. About 3Sv of the model diapycnal upwelling occurring due to strong tidal mixing along the Kurii islands induces a meridional-diapycnal overturning circulation. These results explain the observed features that about 4Sv of the cross-gyre Oyashio transport along the western boundary participate in the formation of NPIW. (3) High-resolution intensive observation using CTD/towed-CTD (MVP : Moving Vessel Profiler) and LADCP/ADCP were performed around the Kuroshio Extension. These observations revealed that intermediate-depth frontal waves with the wavelength of about 200km propagate in the downstream direction with the phase speed of 0.2m/s, amplifying the amplitude. The waves break down and mix the two water masses very efficiently in the downstream regions until 150E. A linear stability analysis reveals that the observed frontal waves are possibly the baroclinically unstable waves due to the coupling between the surface and intermediate-depth vorticity anomalies. The Oyashio water thus enhances intensive mixing and NPIW formation by entering into the Kuroshio Extension. Less

  • Research Products

    (10 results)

All Other

All Publications (10 results)

  • [Publications] I.Yasuda: "North Pacific Intermediate Water : Progress in SAGE and related projects"J.Oceanogr.. 60(2). 385-396 (2004)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] H.Tatebe, I.Yasuda: "The Oyashio southward intrusion and cross-gyre transport related to diapycnal upwelling in the Okhotsk Sea"J.Phys.Oceanogr. (印刷中). (2004)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] M.Masujima, I.Yasuda et al.: "Transport of Oyashio water across the Subarctic Front into the Mixed Water Region and formation of NPIW"J.Oceanogr.. 59. 855-869 (2003)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] I.Yasuda, S.Kouketsu et al.: "Influence of intermediate Okhotsk Sea water on the Oyashio and North Pacific Intermediate Water"J.Geophys.Res.. 107(C12). 3237, doi:10.1029/2001JC001037 (2002)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] T.Hibiya, M.Nagasawa: "Latitudinal dependence of diapycnal diffusivity in the thermocline using a finescale parameterization"Geophysical Research Letters. 31(1). L01301, doi:10.1029/2003GL017998 (2004)

    • Description
      「研究成果報告書概要(和文)」より
  • [Publications] I.Yasuda: "North Pacific Intermediate Water : Progress in SAGE and related projects"J.Oceanogr. 60(2). 385-396 (2004)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] H.Tatebe, I.Yasuda: "The Oyashio southward intrusion and cross-gyre transport related to diapycnal upwelling in the Okhotsk Sea"J.Phys.Oceanog. (in press). (2004)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] M.Masujima, I.Yasuda: "Transport of Oyashio water across the Subarctic Front into the Mixed Water Region and formation of NPIW"J.Oceanogr. 59. 855-869 (2003)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] I.Yasuda, S.Kouketsu, et al.: "Influence of intermediate Okhotsk Sea water on the Oyashio and North Pacific Intermediate Water"J.Geophys.Res.. 107(C12). 3237, doi:10.1029/2001JC001037 (2002)

    • Description
      「研究成果報告書概要(欧文)」より
  • [Publications] T.Hibiya, M.Nagasawa: "Latitudinal dependence of diapycnal diffusivity in the thermocline using a finescale parameterization"Geophysical Research Letters. 31(1). doi:10.1029/2003GL017998 (2004)

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

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Published: 2005-04-19  

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