A study of abyssal circulation based on the expansion in terms of vertical modes incorporating density diffusion

这个项目的目的是通过用垂直模式扩展场并研究每种模式的行为来阐明深海环流的基本动力学。将密度的垂直扩散和水平扩散结合在一起，使所得到的模式直接与普通的三维数值实验相比较。在我们的模式中，深层西部边界层可以是粘性的，也可以是扩散的，这取决于层结和纬度。水平扩散作用强的高层模式往往有广泛的扩散西部边界层。在极地流动(向赤道)的西部边界层中，深水上(下)井，通过密度扩散，深水可以在边界附近甚至内陆地区下沉。用位涡(厚度项)扩散的新概念很好地解释了边界层的结构变化和下沉现象，该概念同样适用于层结海洋的表层。在一个扩展的模式中，研究了孤立的海底地形对深海环流的影响。特别是，通过引入耗散项，我们确定了地岛内部的场，这已经超出了特征线法的范围，发展了一种直接的方法来高效地求解高阶振型，并用于研究海洋环流的垂直结构。

The purpose of this project is to clarify the basic dynamics of abyssal circulation by expanding the field in terms of vertical modes and investigating the behavior of each mode.Incorporating both vertical and horizontal diffusion of density makes the obtained model comparable directly with ordinary three-dimensional numerical experiments.In our model,deep western boundary layers can be either in viscous or in diffusive regimes, depending on the stratification and latitudes.Higher modes,for which horizontal diffusion works strongly,tend to have broad diffusive western boundary layers.In the poleward flowing(equator-ward) western boundary layer,deep water upwells(downwells),while the opposite sign of vertical flow is found in the narrow layer adjacent to the western coast.By virtue of density diffusion,deep water can downwell near boundaries and even in interior regions.The structural change of boundary layers and associated appearance of downwelling were explained well in terms of a new concept of diffusion of(the thickness term of)potential vorticity, which applies as well to surface layers of stratified oceans.In an extended model,effects of isolated bottom topography on abyssal circulation were investigated. In particular,by including dissipative terms,we determined the field inside the geostophic island,which had been beyond the scope the characteristic method.A direct method was developed to solve higher modes efficiently.It was used to investigate the vertical structure of ocean circulation.