| Project/Area Number |
12440125
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | The University of Tokyo |
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Principal Investigator |
HIBIYA Toshiyuki Graduate School of Science, The Univedrsity of Tokyo, Professor, 大学院・理学系研究科, 教授 (80192714)
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| Co-Investigator(Kenkyū-buntansha) |
FURUE Ryo Center for Climate System Research, The University of Tokyo, Research Associate, 気候システム研究センター, 助手 (30311640)
ISODA Yutaka Faculty of Fisheries, Hokkaido University, Associate Professor, 水産学部, 助教授 (10193393)
YOSHIDA Jiro Faculty of Fisherles, Tokyo University of Fisheries, Associate Professor, 水産学部, 助教授 (30174931)
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| Project Period (FY) |
2000 – 2001
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| Project Status |
Completed (Fiscal Year 2001)
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| Budget Amount *help |
¥15,100,000 (Direct Cost: ¥15,100,000)
Fiscal Year 2001: ¥6,500,000 (Direct Cost: ¥6,500,000)
Fiscal Year 2000: ¥8,600,000 (Direct Cost: ¥8,600,000)
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| Keywords | diapycnal mixing / North Pacific / global abyssal circulation / internal tides / inertial frequency / energy cascade / nonlinear interactions / parametric subbarmonic instability / 深層 / Parametric subharmonic instability / 中緯度低気圧 / 3波共鳴干渉機構 / XCP / XCTD観測 |
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| Research Abstract |
The mechanical energy which drives the interior mixing in the oceans is believed to be originally supplied at large scales and then transferred across the deep ocean internal wave spectrum down to small dissipation scales. In recent numerical experiments (Hibiya et al., 1996, 1998, 2002), this energy cascade process was shown to be dominated by parametric subharmonic instabilities which transfer energy from the low vertical wavenumber, double-inertial frequency wave band to a high vertical wavenumber, near-inertial frequency wave band. The resulting enhanced, high vertical wavenumber, nearinertial current shear was shown to play a key role in controlling turbulent mixing processes.
In this study, to test whether or not the numerically predicted energy cascade process is actually dominant in the real deep we deployed a total of 106 expendable current profilers over a large area in the North Pacific to examine the spatial distribution of high vertical wavenumber (vertical wavelength 〜25 m
… More
) shear. At mid latitudes, significant enhancement of the 25-m vertical shear was found over prominent generation regions of semidiurnal internal tides such as the Hawaiian Ridge and the Izu-Ogasawara Ridge where the semidiurnal tidal frequency exceeds twice the local inertial frequency. At high latitudes, in contrast, no significant enhancement of the 25-m vertical shear was found to occur even over another prominent generation region of semidiurnal internaUtides, the Aleutian Ridge, where the semidiurnal tidal frequency is less than twice the local inertial frequency. We find that the observed spatial distribution of the intensity of the 25-m vertical shear correlates very well with that of the low vertical wavenumber, double-inertial frequency internal wave energy numerically predicted by Nagasawa et al. [2000] and Niwa and Hibiya [2001]. This is the first in-situ evidence for the dominant role of parametric subharmonic instability in transferring deep ocean internal wave energy down to small dissipation scales. This study provides a theoretical framework for future attempts to determine the large-scale structure of mixing over the world's oceans. Less
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