2006 Fiscal Year Final Research Report Summary
Quantification of the intensity of mixing hotspots to clarify the dynamics of the global meridional overturning circulation
| Project/Area Number |
17340139
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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 (80192714)
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| Co-Investigator(Kenkyū-buntansha) |
ISODA Yutaka Hokkaido University, Graduate School of Fisheries Science, Associate Professor (10193393)
KITADE Yujiro Tokyo University of Marine Science and Technology, Faculty of Marine Science, Associate Professor (50281001)
HASUMI Hiroyasu The University of Tokyo, Center for Climate System Research, Associate Professor (40311641)
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| Project Period (FY) |
2005 – 2006
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| Keywords | Diapycnal diffusivity / Mixing hotspots / Global map / Latitudinal dependence / Internal tides / Microstructure profiler / Meridional overturning circulation / Expendable current profilers |
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| Research Abstract |
The un-tethered free-fall microstructure profiler “TurboMAP-D" was used to collect a total of 53 velocity microstructure profiles in the interior of the Pacific Ocean. We found the diapycnal diffusivity at 20°-30°N was roughly in proportional to the logarithm of the locally available energy density of the semidiurnal internal tide and reached more than 10^<-4> m^2s^<-1> near the Izu-Ogasawara Ridge. In contrast, diapycnal diffusivity was found to remain of the order of〜10^<-5> m^2s^<-1> poleward of 30°N and equatorward of 20°N, irrespective of the amount of locally available semidiurnal internal tide energy. We have confirmed that these observed features are consistent with the global map of diapycnal diffusivity in the main thermocline predicted by Hibiya et al. (2006).
Using an idealized ocean general circulation model, we next examined the effect of“mixing hotspots", predicted by Hibiya et al. (2006), on the meridional overturning circulation of the Pacific Ocean. We have found that the estimated upwelling in the mixing hotspots is not sufficient to balance deep-water production. In addition, the northward transport of the deep water crossing the equator was found to be much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation for these results is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated from observations. We raise doubts about the validity of previous ocean general circulation models where diapycnal diffusivity is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys.
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Research Products
(40 results)
