Topographic Rectification on the Continental Margin: Toward Detectability from Observations

在大陆架和陆坡上，通常发现平均（月）流量是沿自由亚惯性海岸陷波传播方向（例如美国西海岸向北）。在这个意义上，有许多潜在的机制可以产生流动，其中一些机制已经得到了充分的研究，我们有实际的诊断方法可以与观测一起使用，因此我们可以测试给定的机制（例如潮汐整流）是否负责。一个潜在的重要机制，是不容易诊断的观察是形式压力。这一机制实质上反映了沿沿着水流的基本不对称性。与CTW相反的流动（这些流动只能在一个方向上传播相位）可能会遇到碰撞并建立驻波（具有零相速度且看起来稳定）。这种驻波对流体产生阻力。另一方面，CTW意义上的流动不允许驻波形成（因为流动仅加速波传播），并且不会产生形状应力。这种潜在的不对称性意味着在一个颠簸的底部上的零平均强迫可以导致平均流的产生。这种机制以前已经解决了一些理想化的上下文中，它的使用已被证明可以提高性能的粗网格仿真模型。本研究要求通过将应力模型扩展到具有有限大陆架和坡度以及密度分层的现实参数区域来提高我们的知识。将系统地利用区域海洋模拟系统来研究这一现实的参数范围，并根据可观察到的输入数据，得出整流流量的定量经验表达式。为了达到本项目的主要目标，这组数值试验是必要的：定义可用于现有或可实现的观测的试验，以明确地确定地形校正在特定环境中是否重要。本项目成功执行的智力价值是双重的：1）将地形校正模型系统地扩展到以前没有探索过的实际参数范围，以及2）定义一组诊断测试，可以明确地用于检测（或消除）地形校正，作为驱动平均沿岸流和上升流的手段。该项目的更广泛影响同样是双重的：1）改进海洋模型，这对气候和生态预报是有用的，2）作为一种手段，向本科生介绍科学研究和方法。如果这项提议得到资助，伍兹霍尔海洋研究所将为这个项目捐款5,000美元，以帮助支付暑期学生的费用。

Over the continental shelf and slope, mean (over months) flow is very often found to be in the direction of free subinertial coastal-trapped wave (CTW) propagation (e.g. northward off the west coast of the United States). There are many potential mechanisms that could generate flow in this sense, and some of these are sufficiently well-studied that we have practical diagnostics to use with observations, and thus we can test whether a given mechanism (e.g. tidal rectification) is responsible. One potentially important mechanism that is not readily diagnosed from observations is form stress. This mechanism is essentially a reflection of the underlying asymmetry of flows along a coastline. Flows in the opposite sense to CTW (these can only propagate phase in one direction) generation can encounter a bump and set up a standing wave (one that has zero phase velocity and appears steady). This standing wave exerts a drag on the flow. On the other hand, flow in the sense of CTWs does not allow a standing wave to form (since the flow only accelerates wave propagation), and no form stress can result. This underlying asymmetry means that zero-mean forcing over a bumpy bottom can result in a mean flow generation. This mechanism has previously been addressed in a number of idealized contexts, and its use has been shown to improve performance of coarse-grid simulation models. The present study calls for advancing our knowledge by extending form stress model development into the realistic parameter regime with a finite shelf and slope, and with density stratification. The Regional Ocean Modeling System (ROMS) will be used systematically to study this realistic parameter range, and to generate a quantitative empirical expression for rectified flow, given observable inputs. This set of numerical experiments is necessary in order to reach the main goal of this project: to define tests that can be used with existing or realizable observations to determine unambiguously whether topographic rectification is important in a particular setting.The intellectual merit of a successful execution of this project is twofold: 1) a systematic extension of topographic rectification models into a realistic parameter range not previously explored, and 2) the definition of a set of diagnostic tests that can used unambiguously to detect (or eliminate) topographic rectification as a means for driving mean alongshore flow and upwelling. Mean flow is particularly important since it dominates advective processes.The broader impact of this project is likewise twofold: 1) making improvements in ocean models that should be useful in climate and ecological forecasting, and 2) serving as a means to introduce an undergraduate student to scientific research and methodology. Should this proposal be funded, Woods Hole Oceanographic Institution will contribute $5,000 to this projectto help defray the costs of the summer student.