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.

研究了海洋温盐环流的缓慢动力学，重点研究了密度扩散的作用，密度扩散引起水柱的“扩散拉伸”，从而引起“位涡扩散”。建立了三个框架：(1)扩散减重模型；(2)扩散垂直模态的扩展模型；(3)扩散准地转模型。这些框架被证明是非常有用的，使我们能够分析和理解温盐环流的三维结构，这很难从普通的观点来解释。本研究以可理解的方式从三个方面深化和补充了斯托梅尔和阿伦斯的研究。首先，我们的框架揭示了由于黏度和密度扩散等耗散过程导致的边界层结构。其次，从三个概念框架阐述了维持三维循环场的动力学。从动力学角度系统地解释了大气对温盐环流的影响。我们特别感兴趣的结果如下。1)密度的水平扩散将边界层分为“粘性”和“扩散”两种状态。如果考虑到密度的水平扩散，即使在深海层中，水也可以向下渗透。2)耗散过程的引入解决了地转岛附近的稳定环流问题，地转等高线在地转岛附近彼此接近；低压盛行，上升流变得非常微弱甚至逆转。(3)在有底地形或无底地形的情况下，将扩散垂向模态作为规定力的解，得到了与数值实验结果一致的三维环流。扩散准地转模式虽然高度简化，但比扩散垂直模态的展开方法更直接地提供了一种理解温盐环流三维结构的方法。少

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 … More 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