2007 Fiscal Year Final Research Report Summary
Numerical study about heat and salinity transports induced by small disturbances in an ocean general circulation
| Project/Area Number |
18540436
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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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 | Japan, Meteorological Research Institute |
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Principal Investigator |
HIRABARA Mikitoshi Japan, Meteorological Research Institute, Oceanographic Research Department, Senior Researcher (70354545)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIZAKI Hiroshi Meteorological Research Institute(MRI), Oceanographic Research Department, Director (60354544)
YAMANAKA Goro Meteorological Research Institute(MRI), Oceanographic Research Department, Senior Researcher (60442745)
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| Project Period (FY) |
2006 – 2007
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| Keywords | Ocean general circulation model / Small scale disturbances / Diffusivity parameterization |
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| Research Abstract |
Results from an eddy-resolving model (grid-size<10km; R-grid) and an eddy-permitting model (20km; P-grid) were compared to understand the reason why R-grid model can simulate the ocean climatology better than P-grid. A parameterization of sub-grid transport was developed using the framework of turbulent diffusion scheme. The parameterization was implemented to a P-grid model and validated.
The subtropical mode water and the subtropical countercurrent are realistically simulated in a R-grid North Pacific model (NPERM5), while they are poorly simulated in a P-grid model (NPERM15).
The intermediate salinity minimum can be better represented in NPERM5 than in NPERM15, because cold fresh Oyashio water and warm saline Kuroshio water mix vigorously activated by numbers of filament-like small-wale disturbances in the R-grid model The eddy-induced thickness diffusivity and the isopycnal diffusivity coefficients were estimated in the Oyashio-Kuroshio mixed water region. The magnitudes of the coefficients are generally smaller in P-grid model than R-grid. The isopycnal coefficient is larger than thickness in the R-grid model Therefore, the primary reason why the salinity minimum cannot be simulated in P-grid model is the very weak isopycnal mixing in it.
Decomposing the variables at R-grids into the spatial average and the anomalies from it over a P-grid, the sub-grid transport (SGT) fir the P-grid can be calculated. The three-dimensional anti-symmetric mixing tensor consistent with the horizontal SGT of density was formulated. The sub-grid heat and salinity transport can be realized through the diffusive flux corresponding to this tensor. The parameterization implemented in a P-grid model activates the isopycnal mixing and improves the result.
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