Topographic Rectification on the Continental Margin: Toward Detectability from Observations

大陆边缘的地形校正：通过观测实现可探测性

• 批准号: 0751731
• 负责人: Kenneth Brink
• 金额: $ 46.41万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0751731&HistoricalAwards=false
• 关键词: Topographic; Rectification; Continental; Margin; Toward

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.

在大陆架和大陆坡上，平均（几个月内）流量经常被发现沿着自由亚惯性海岸捕获波（CTW）传播的方向（例如，从美国西海岸向北）。从这个意义上讲，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，我们可以通过观察来进行实用的诊断，因此我们可以测试给定的机制（例如潮汐整流）是否负责。一种不易通过观察诊断的潜在重要机制是形式压力。这种机制本质上反映了沿海岸线流动的潜在不对称性。与 CTW 相反的流动（它们只能在一个方向上传播相位）生成可能会遇到碰撞并建立驻波（相速度为零且看起来稳定的驻波）。该驻波对流动施加阻力。另一方面，CTW 意义上的流动不允许形成驻波（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凹凸不平的底部上的零均值强迫可能会导致平均流的产生。该机制之前已在许多理想化环境中得到解决，并且其使用已被证明可以提高粗网格仿真模型的性能。本研究呼吁通过将形状应力模型开发扩展到具有有限架和坡度以及密度分层的实际参数范围来推进我们的知识。区域海洋模拟系统（ROMS）将被系统地用于研究这一现实参数范围，并在给定可观测输入的情况下生成修正流量的定量经验表达式。为了实现该项目的主要目标，这组数值实验是必要的：定义可与现有或可实现的观测一起使用的测试，以明确确定地形校正在特定环境中是否重要。成功执行的智力价值该项目有两个方面：1）将地形校正模型系统地扩展到以前未探索过的实际参数范围，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：驱动手段是指沿岸流和上升流。平均流尤其重要，因为它主导平流过程。该项目的更广泛影响同样是双重的：1）改进海洋模型，这对气候和生态预测有用，2）作为介绍本科生的一种手段科学研究和方法论。如果该提案获得资助，伍兹霍尔海洋研究所将向该项目捐款 5,000 美元，以帮助支付暑期学生的费用。