Wind-Driven Mixing below the Oceanic Mixed Layer
Wind-Driven Mixing below the Oceanic Mixed Layer
复制标题
DOI：
10.1175/jpo-d-10-05020.1
复制
发表时间：
2011-08
影响因子：
3.5
通讯作者：
A. Grant;Stephen E. Belcher
中科院分区：
文献类型：
--
作者：
A. Grant;Stephen E. Belcher
本文采用大涡模拟方法，研究了在无科里奥利力的情况下，海洋上层边界层在恒定表面应力作用下的湍流过程。发展的边界层具有两层结构，即在分层剪切层之上的充分混合层。混合层的深度近似恒定，而剪切层的深度随时间增加。湍流动量通量从剪切层表面到底部近似线性变化。在混合层底部，通过剪切产生的湍流有一个最大值。剪切产生的大小随时间增加。这种增加主要是由于边界层深度增加而使混合层底部动量通量增加的结果。剪切湍流的长度尺度是边界层深度。一个简单的缩放建议的剪切生产的大小取决于表面强迫和平均混合层电流。这种标度可以用平均动能通量的散度来解释。一个简单的整体模型的边界层得到方程描述的混合层和边界层深度随时间的变化。该模型表明，边界层加深的速度不依赖于温跃层的分层。整体模型表明，只要表面浮力通量小，混合层深度的变化就很小。
This study describes the turbulent processes in the upper ocean boundary layer forced by a constant surface stress in the absence of the Coriolis force using large-eddy simulation. The boundary layer that develops has a two-layer structure, a well-mixed layer above a stratified shear layer. The depth of the mixed layer is approximately constant, whereas the depth of the shear layer increases with time. The turbulent momentum flux varies approximately linearly from the surface to the base of the shear layer. There is a maximum in the production of turbulence through shear at the base of the mixed layer. The magnitude of the shear production increases with time. The increase is mainly a result of the increase in the turbulentmomentumfluxatthebaseofthemixedlayerduetotheincreasein thedepthoftheboundarylayer. The length scale for the shear turbulence is the boundary layer depth. A simple scaling is proposed for the magnitude of the shear production that depends on the surface forcing and the average mixed layer current. The scaling can be interpreted in terms of the divergence of a mean kinetic energy flux. A simple bulk model of the boundary layer is developed to obtain equations describing the variation of the mixed layer and boundary layer depths with time. The model shows that the rate at which the boundary layer deepens does not depend on the stratification of the thermocline. The bulk model shows that the variation in the mixed layer depth is small as long as the surface buoyancy flux is small.