SGER: Mixing in a Tidally Modulated Boundary Layer over Rough Topography

SGER：在粗糙地形上的潮汐调制边界层中混合

• 批准号: 0411938
• 负责人: Sutanu Sarkar
• 金额: $ 6万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-02-15 至 2005-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0411938&HistoricalAwards=false
• 关键词: SGER; Mixing; Tidally; Modulated; Boundary

0411938Tidally generated internal waves at long-wavelength bottom topography that are radiated into the interior to subsequently breakdown into small scales may be a significant contributor to diapycnal mixing. The interaction of the tide with smaller-scale topography is also relevant to near-field mixing as exemplified by recent data from moored instruments taken as part of the Hawaii Ocean Mixing Experiment (HOME) near-field survey that indicate increased levels of dissipation and variability in a rather thick bottom region, O(250)m, depending on the tidal phase. The mixing characteristics of a stratified current oscillating on a rough slope with M2 tidal period are poorly understood. High-accuracy, numerical simulations with a non-hydrostatic model will be conducted to understand the relevant processes underlying the observed behavior of the bottom boundary layer. The modulation by a M2 tide of a current in the deep ocean over rough topography is considered. In the model problem, a shallow slope represents the large-scale topography while Gaussian roughness elements of specified height and pitch represent the small-scale topography. The value of the Brunt-Vaisala frequency, near the bottom changes in response to the tidal modulation, and the interaction of the time-dependent stratification with the current as it accelerates, decelerates or potentially separates over the small-scale roughness is of interest. The physics relevant to this problem is fundamentally different from the internal wave generation problem and, although important, has been much less studied than the latter. The Large Eddy Simulation will be performed with advanced numerical methods for the unsteady, three-dimensional, Navier-Stokes equations in primitive form without any hydrostatic assumption. The subgrid model to be used is a dynamic mixed model with wall-layer modeling. A generalized coordinate formulation allows the grid to track the bottom topography, helpful for maintaining accuracy. Parameters relevant to the HOME situation will be chosen in conjunction with HOME PI's. The scaling of the effective boundary layer thickness and profiles of the Vaisala frequency, buoyancy flux, fluctuation intensities and eddy diffusivities as a function of important nondimensional parameters will be obtained. Broader Impacts: The results of the proposed research will help understand the link between the mixing observed in an unexpectedly thick region near the bottom and the M2 tidal modulation and thus impact physical oceanography. Given our lack of knowledge about mixing in an oscillating boundary layer over rough topography in a stratified, rotating medium, it is expected that this study will result in a substantive contribution to geophysical fluid dynamics as well.

0411938在长波长海底地形处潮汐产生的内波辐射到内部，随后分解成小尺度，这可能是纵摇混合的重要贡献者。潮汐与小尺度地形的相互作用也与近场混合有关，作为夏威夷海洋混合实验（HOME）近场调查的一部分，最近从系泊仪器获得的数据表明，在相当厚的海底区域，O（250）m，取决于潮汐阶段，耗散和变化水平增加。在粗糙斜坡上振荡的具有M2潮周期的分层流的混合特性知之甚少。将使用非流体静力学模型进行高精度数值模拟，以了解所观察到的底部边界层行为的相关过程。考虑了M2潮汐对深海中粗糙地形上海流的调制作用。在模型问题中，浅斜坡代表大尺度地形，而指定高度和间距的高斯粗糙度元素代表小尺度地形。的Brunt-Vaisala频率的值，底部附近的变化响应于潮汐调制，和随时间变化的分层与电流的相互作用，因为它加速，减速或可能分离的小尺度粗糙度的兴趣。与这个问题相关的物理学与内波产生问题有着根本的不同，虽然很重要，但研究得比后者少得多。大涡模拟将采用先进的数值方法对原始形式的非定常、三维、Navier-Stokes方程进行，而无需任何流体静力学假设。所使用的子网格模型是具有壁层建模的动态混合模型。广义坐标公式允许网格跟踪底部地形，有助于保持精度。将结合HOME PI选择与HOME情况相关的参数。将获得作为重要无量纲参数的函数的有效边界层厚度和Vaisala频率、浮力通量、波动强度和涡流扩散率的剖面的缩放。更广泛的影响：拟议研究的结果将有助于了解在底部附近意外厚的区域观察到的混合与M2潮汐调制之间的联系，从而影响物理海洋学。由于我们缺乏知识的混合在一个振荡的边界层在粗糙的地形分层，旋转介质，预计这项研究将导致在地球物理流体动力学的实质性贡献。