Collaborative Research: Direct Estimation of Topographic Form Drag from Seafloor pressure Measurement

合作研究：通过海底压力测量直接估计地形阻力

• 批准号: 0751930
• 负责人: James Moum
• 金额: $ 80.95万
• 依托单位: Oregon State University
• 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: 2008-06-01 至 2012-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0751930&HistoricalAwards=false
• 关键词: Collaborative; Research; Direct; Estimation; Topographic

The importance of topographic form drag to atmospheric circulation has long been recognized. It has been examined in detail via field experiments, laboratory, numerical and theoretical studies. Significantly, it has been directly measured by high-resolution pressure sensors deployed across mountain ranges, the critical topographic elements in the atmosphere. These direct measurements have provided the important link allowing detection/prediction of high drag states from established synoptic weather stations. Mountain drag parameterizations are now incorporated in numerical models of atmospheric circulation. It has been long thought that form drag is important to oceanic flows, as well. In particular, the Antarctic Circumpolar Current may be largely controlled by form drag. Coastal flows in which rapidly-flowing jets or barotropic tidal currents pass over varying topography are prime candidates for developing high drag states. Yet form drag is not incorporated in either global or coastal circulation models. Rather, the effects of unresolved bottom interactions are typically included in the form of quadratic drag laws, despite the fact that during high drag states, bottom friction is known to be a small component of total drag, as has been observed over coastal ocean topographic features. Part of the reason for not recognizing the importance of form drag to ocean circulation has been our inability to clearly document variations in time, space and form of high drag states. In turn this has impeded a first-order understanding of these phenomena. Intellectual Merit: Oceanic time scales are longer and spatial scales shorter than atmospheric. Hence, comprehensive and synoptic measurements of the physical processes leading to form drag in oceanic flows can be more easily obtained. The understanding gained in interpreting these measurements will contribute to our understanding of geophysical high drag flow in general.The investigators have recently demonstrated a new measurement that permits detection of the seafloor pressure signal of nonlinear internal waves and propose to implement this measurement in a manner analogous to surface pressure measurements across mountain ranges to determine the form of high drag states across a small, relatively two-dimensional coastal bump, temporal variability of the total drag and relationship to the large-scale flow; and the effectiveness of employing this measurement at other critical ocean sites. The project will include initial testing of the pressure sensor and a pilot project where moored and intensive profiling measurements will provide synoptic water column density and velocity measurements to supplement those from a seafloor pressure sensor array. From these observations and complementary modeling efforts, Froude number-based parameterizations will be proposed for testing in coastal circulation models. Broader Impact: Mountain drag produces a recognized and critical influence on atmospheric circulation and must be parameterized in global circulation models. Lack of inclusion in ocean circulation models may be an oversight. Identification of its oceanic influence (or lack thereof) seems long overdue. A simple and easily-deployed measurement that will allow long time series of pressure drag at various critical global locations will help to identify its magnitude and variability. Training in state-of-the-art ocean modeling will be provided to a graduate student.

地形阻力对大气环流的重要性早已被人们认识到。通过现场实验、实验室、数值和理论研究对其进行了详细检查。值得注意的是，它是通过部署在山脉（大气中的关键地形要素）上的高分辨率压力传感器直接测量的。这些直接测量提供了重要的链接，允许从已建立的天气站检测/预测高阻力状态。山地阻力参数化现已纳入大气环流数值模型中。 长期以来，人们一直认为形状阻力对于海洋流动也很重要。特别是，南极绕极流可能很大程度上受形状阻力的控制。快速流动的急流或正压潮汐流经过不同地形的海岸流是形成高阻力状态的主要候选者。然而，形状阻力并未纳入全球或沿海环流模型中。相反，未解决的底部相互作用的影响通常以二次阻力定律的形式包含在内，尽管事实上在高阻力状态下，已知底部摩擦力只占总阻力的一小部分，正如在沿海海洋地形特征上观察到的那样。 没有认识到形状阻力对海洋环流的重要性的部分原因是我们无法清楚地记录高阻力状态的时间、空间和形状的变化。反过来，这又阻碍了对这些现象的初步理解。 智力优点：海洋时间尺度比大气更长，空间尺度更短。因此，可以更容易地获得导致海洋流中形成阻力的物理过程的全面和概要测量。在解释这些测量结果中获得的理解将有助于我们对地球物理高阻力流的总体理解。研究人员最近展示了一种新的测量方法，可以检测非线性内波的海底压力信号，并建议以类似的方式实现这种测量跨越山脉的表面压力测量，以确定跨越较小的、相对二维的海岸隆起的高阻力状态的形式、总阻力的时间变化以及与大规模流量的关系；以及在其他关键海洋地点采用这种测量的有效性。该项目将包括压力传感器的初步测试和一个试点项目，其中停泊和密集剖面测量将提供天气水柱密度和速度测量，以补充海底压力传感器阵列的测量结果。根据这些观察结果和补充建模工作，将提出基于弗劳德数的参数化，用于沿海环流模型的测试。 更广泛的影响：山地阻力对大气环流产生公认的关键影响，必须在全球环流模型中参数化。海洋环流模型中缺乏内容可能是一个疏忽。确定其海洋影响（或缺乏影响）似乎早就应该了。一种简单且易于部署的测量方法将允许在全球各个关键位置进行长期压力阻力序列，这将有助于确定其大小和变化性。 将为研究生提供最先进的海洋建模培训。