1995 Fiscal Year Final Research Report Summary
A study of the three-dimensional structure of ocean thermohaline circultaion with coneptual models based on the diffusion of potential vorticity due to the diffusion of density.
| Project/Area Number |
06804024
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
MASUDA Akira Research Institute for Applied Mechanics, Kyushu University ; Professor, 応用力学研究所, 教授 (60091401)
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| Co-Investigator(Kenkyū-buntansha) |
KUSABA Tadao Research Institute for Applied Mechanics, Kyushu University ; Associate Professo, 応用力学研究所, 助教授 (00037871)
UEHARA Katsuto Research Institute for Applied Mechanics, Kyushu University ; Research Associate, 応用力学研究所, 助手 (80223494)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Ocean Thermohaline Circulation / Three-Dimensional Structure / Diffusive Reduced-Gravity Model / Diffusive Vertical Modes / Diffusive Quasi-Geostrophic Model / Diffusion of Potential Vorticity / Diffusive Strethcing / Topograhic Effects |
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| Research Abstract |
The slow dynamics of ocean thermohaline circulation was investigated with emphasis on the role of the diffusion of density, which induces the "diffusive stretching" of water columns and consequently the "diffusion of potential vorticity". Three frameworks were developed : (1) a diffusive reduced-gravity model, (2) expansion in terms of diffusive vertical modes, and (3) a diffusive quasi-geostrophic model. These frameworks turned out quite useful, allowing us to analyze and understand the three-dimensional structure of thermohaline circulation, which would be difficult to interpret from ordinary viewpoints.
The present study deepened and supplemented that of Stommel and Arons in three ways in a comprehensible manner. First, our frameworks reveal the sturcture of bondary layres due to dissipative processes such as viscosity and diffusion of density. Second, the dynamics that mantains the three-dimensional circulation field was elucidated in terms of three conceptual frameworks. Third, top
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ogrpahic effects on thermohaline circulation were explained systematically in dynamical terms.
Results of particular interest are as follows.
1) Horizontal diffusion of density separates two regimes of boundary layrs : "viscous" and "diffusive" regimes. Water can downwell even in abyssal layrs when horizontal diffusion of density is incorporated.
2) Introduction of dissipative processes resolves the problem of the steady circulation near a geostrophic island, within which geostrophic contours close on themsleves ; low pressure prevails and upwelling becomes very feeble or even reversed.
3) The diffusive vertical modes as the solutions to prescribed forcings are synthesized to give three-dimensinal circulations which agree well with those obtained by numerical experiments, either with or without bottom topography.
Though highly simplified, the diffusive quasi-geostrophic model provides a means by which to understnad the three-dimensional strucutre of thermohaline circulation much more directly than the method of the expansion in terms of diffusive vertical modes. Less
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