2003 Fiscal Year Final Research Report Summary
Global mapping of diapycnal mixing rates in the deep ocean
| Project/Area Number |
14340136
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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 The University of Tokyo, Graduate School of Science, Professor, 大学院・理学系研究科, 教授 (80192714)
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| Co-Investigator(Kenkyū-buntansha) |
HASUMI Hiroyasu The University of Tokyo, Center of Climate System Research, Research Associate, 気候システム研究センター, 助手 (40311641)
ISODA Yutaka Hokkaido University, Faculty of Fisheries, Associate Professor, 大学院・水産科学研究科, 助教授 (10193393)
YOSHIDA Jiro Tokyo University of Marine Science and Technology, Faculty of Marine Science, Professor, 海洋科学部, 教授 (30174931)
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| Project Period (FY) |
2002 – 2003
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| Keywords | Diapycnal mixing / Latitudinal dependence / Global thermohaline circulation model / Semidiurnal internal tides / Parametric subharmonic instability / Energy cascade / Near inertial current shear / Expendable current profiler |
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| Research Abstract |
Global mapping of diapycnal mixing rates in the thermocline is essential to improve the ability of global thermohaline circulation models in predicting future climate changes. For this purpose, we have first estimated diapycnal mixing rates over a large area in the interior of the North and South Pacific, the North Atlantic and the South Indian Ocean by incorporating the fine-scale vertical shear of horizontal velocity measured by expendable current profilers (XCP) into Gregg's formula (Gregg, 1989). The remarkable finding from the XCP survey is that the estimated diapycnal mixing rate in the thermocline is strongly dependent on the latitude.
Then, these estimates have been related to the main energy source for diapycnal mixing, the semidiumal internal tide energy numerically calculated at each location, and an empirical formula has been found to predict the global distribution of diapycnal mixing rates in the deep ocean. Incorporating the numerically predicted semidiurnal internal tide energy at each longitude and latitude into the resulting empirical formula, we have found that strong diapycnal mixing (mixing hotspot) is limited to prominent topographic features at latitudes 20^0 -30^0 where the available semidiurnal internal tide energy can be efficiently transferred to dissipation scales by resonant interactions amongst internal waves called parametric subharmonic instability.
Embedding the obtained distribution of diapycnal mixing rates into global thermohaline circulation models should yield significant improvement in their ability to predict future climate change.
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