内潮致拉格朗日余流的数值研究

Numerical Study of the Lagrangian Residual Velocity Induced by Internal Tide

利用MITgcm数值模式,研究了单海脊地形下的内潮致拉格朗日余流,发现余流结构与内潮结构相对应,从海脊附近沿波射线分布,向东、西两方向流动。与欧拉余流相比,拉格朗日余流在海脊附近呈现辐散的特征,欧拉余流则表现为辐聚的特征。改变地形、正压潮流速等参数,拉格朗日余流结构随之变化。当海脊变宽时,余流随波射线的消失而变得很小且混乱;当海脊变高时,海脊附近逐渐产生向海底方向的流动,与海面反射的余流形成平行的射线,余流整体增强,海脊附近的余流在向外流动过程中增幅减小;当正压潮流速增大时,余流结构基本不变,但在高窄海脊地形下海脊附近的平行射线会逐渐合为一支从海脊顶部产生的流动。

In this study,the MITgcm(MIT General Circulation Model)is applied to study the Lagrangian residual velocity(LRV)induced by internal tide in a 2-D ridge model sea.It is found that the pattern of LRV corresponds well to the baroclinic velocity field.Water flows both eastward and westward from the ridge,and the direction of vertical motion is same as that of the internal wave beam.The distribution of LRV shows divergence near the ridge,but Eulerian residual velocity takes on the convergent feature.Moreover,the structure of LRV changes with the variation of topography and barotropic velocity.When the ridge becomes wider,the LRV gradually weakens and gets more complex with the disappearance of wave beams.As the ridge gets higher,the LRV strengthens all over the region especially near the ridge.If the forced barotropic velocity is increased,the pattern of LRV remains unchanged basically,but the beam turns out to be wider,which is more apparent in the case of high and narrow ridge.