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，着重讨论了密度扩散的作用，密度的扩散导致水柱的“扩散伸展”，从而导致“位涡的扩散”。建立了三个框架：(1)扩散减重模式，(2)扩散垂直模展开式，(3)扩散准地转模式。这些框架被证明是非常有用的，使我们能够分析和理解用普通观点难以解释的温盐环流的三维结构。本研究以一种可理解的方式从三个方面深化和补充了Stommel和Arons的研究。首先，我们的框架揭示了由于密度的粘性和扩散等耗散过程而导致的边界层的结构。其次，从三个概念框架阐述了三维环流场的动力学。第三，顶级…从动力学的角度系统地解释了地貌对温盐环流的影响，主要结果如下：1)密度的水平扩散将边界层分为粘性和扩散两个区域。2)引入耗散过程，解决了地转岛附近的稳定环流问题，在此过程中，地转等值线靠近地转岛；低压占优势，上升流变得非常微弱甚至逆转。3)合成了扩散垂直模作为特定强迫的解，得到了与数值实验结果相一致的三维环流，无论有或没有海底地形。扩散准地转模式虽然非常简化，但它提供了一种比从扩散垂直模的扩展方法更直接地理解温盐环流三维结构的方法。较少

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