Laboratory Simulation of Field Measurements of the Bottom Boundary Layer

海底附近的湍流区有丰富的动力过程。这个区域可以方便地认为是由重叠的湍流底部边界层（TBBL）和湍流底部混合层（TBML）。由于沿着等深线流动的普遍性和它们的相对简单性，最近对沿边界沿着紊流区的许多研究都是在这些条件下进行的;例如，沿着海岸线和山脊流动。在过去的几十年里，野外实验，加上理论和数值模拟的努力，加深了我们对这个边界区域的理解。然而，我们的知识存在差距。例如，需要（i）更好地理解TBBL和TBML之间的关系，（ii）获得更多关于湍流Ekman层停滞的信息，因为它在某些现场计划中观察到，而在其他计划中没有观察到，（ii）对双对数边界层的出现存在争议，以及（iv）希望更好地组织和巩固从海洋湍流边界层的各种现场测量中获得的知识，使之成为某种统一的整体。该项目的智力价值在于有可能清楚地表明，采用湍流的实验室模拟能够或不能定量地模拟海洋边界层。所考虑的物理系统是在背景旋转存在下分层流体的沿着等深线流动。拟议研究的第一个目标是表明，海洋的TBBL可以在实验室中使用足够大的旋转平台进行模拟。为了做到这一点，实验室模拟将直接与现有的实地数据进行比较，这些数据来自对沿着布莱克外脊的北大西洋深海西部边界流的深水流动以及沿着北方加州架的冬季和夏季沿着流的研究。这些与海洋数据的直接比较也将揭示TBBL和TBML之间的关系。第二个目标是概括数据的底部剪切应力，边界层深度和地转流和底部剪切应力之间的角度的外部参数的系统，这些参数包括斜率伯格数，归一化时间从实验开始和参数定义的表面粗糙度。相似性要求证明，在许多工程流动中，当雷诺数变大时，流动特性变得与雷诺数无关，这一条件称为雷诺数相似性。如果这个项目能够成功地用一套明确的参数确定海底边界层的总体特征，其中许多可以远程测量。此外，该项目将支持国际科学，并为美国和法国学生提供在国际氛围中互动的机会。

The turbulent region near the ocean floor is rich in dynamical processes. This region can be conveniently thought of as consisting of overlapping turbulent bottom boundary layers (TBBL) and turbulent bottom mixed layers (TBML). Because of the ubiquitous nature of flows along isobaths and their relative simplicity, much of the recent research on turbulent regions along boundaries has been performed under these conditions; e.g., flows along coastlines and ridges. Field experiments, coupled with theoretical and numerical modeling efforts during the past several decades have sharpened our understanding of this boundary region. There are gaps in our knowledge, however. There is a need, for example, to (i) have an improved understanding of the relation between the TBBL and the TBML, (ii) to have more information on Ekman layer arrest for turbulent flows because it is observed in certain field programs and not in others, (ii) there is controversy on the occurrence of double log boundary layers and (iv) it is desirable tobetter organize and consolidate the knowledge gained from various field measurements on oceanic turbulent boundary layers into some sort of unified whole. The intellectual merit of the project lies in the possibility of demonstrating clearly that laboratory simulations employing turbulence can or cannot quantitatively simulate oceanic boundary layers. The physical system considered is the along isobath flow of a stratified fluid in the presence of background rotation. The first objective of the proposed research is to show that the ocean's TBBL can be simulated in the laboratory using a sufficiently large rotating platform. To accomplish this, the laboratory simulations are to be compared directly with existing field data from studies of the deep water flow of the North Atlantic Deep Western Boundary Current along the Blake Outer Ridge and the winter and summer-time along isobath currents along the Northern California Shelf. These direct comparisons with ocean data will also shed light on the relation between the TBBL and the TBML. The second objective is to generalize data on the bottom shear stress, boundary layer depth and angle between the geostrophic flow and the bottom shear stress in terms of the external parameters of the system; these include the slope Burger number, the normalized time from the beginning of the experiment and parameters defining the surface roughness. Similarity will require the proof that, as in many engineering flows that as the Reynolds number becomes large, the flow characteristics become independent of the Reynolds number, a condition termed Reynolds number similarity.Broader impacts: This project will have broad impact on the range of oceanographic sub-disciplines if it can be successful in defining gross features of the bottom boundary layer in terms of a clear set of parameters, many of which can be measured remotely. Additionally the project will support international science and provide US and French students opportunities to interact in an international atmosphere.