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

地形阻力对大气环流的重要性早已被认识到。通过野外实验、实验室、数值和理论研究，对其进行了详细的检验。值得注意的是，它是由部署在山脉上的高分辨率压力传感器直接测量的，山脉是大气中的关键地形要素。这些直接测量提供了重要的联系，使从已建立的天气气象站探测/预测高阻力状态成为可能。山体阻力参数化现已被纳入大气环流的数值模式。长期以来，人们一直认为形式阻力对海洋流动也很重要。特别是，南极绕极流可能在很大程度上受到形式阻力的控制。快速流动的急流或正压潮流流经不同地形的海岸流是形成高阻力状态的主要候选者。然而，无论是全球环流模式还是沿海环流模式，都没有考虑形状阻力。相反，未解决的海底相互作用的影响通常以二次阻力定律的形式包括在内，尽管在高阻力状态下，海底摩擦是已知的总阻力的一小部分，正如在沿海海洋地形特征上所观察到的那样。没有认识到形式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在时间、空间和形式上的变化。反过来，这又阻碍了对这些现象的一级理解。智力优势：海洋的时间尺度比大气长，空间尺度短。因此，可以更容易地获得导致海洋流动中形成阻力的物理过程的全面和天气学测量。研究人员最近展示了一种新的测量方法，可以探测到非线性内波的海底压力信号，并建议以类似于跨山脉表面压力测量的方式来实施这种测量，以确定相对二维的小型海岸颠簸上的高阻力状态的形式、总阻力的时间变化性以及与大尺度流动的关系；以及在其他关键海洋站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，在该项目中，系泊和密集的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。根据这些观测和补充的模拟工作，将提出基于弗劳德数的参数化在海岸环流模式中进行试验。更广泛的影响：山脉阻力对大气环流产生公认的关键影响，必须在全球环流模式中进行参数化。海洋环流模型中没有包括在内可能是一个疏忽。对其海洋影响(或缺乏影响)的认识似乎早就该有了。一种简单且易于部署的测量将允许在不同关键全球位置的压力阻力的长时间序列，这将有助于确定其大小和变异性。将为研究生提供最先进的海洋建模培训。

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.