Oceanic Fronts, Subduction and Spin-up: Nonlinear Ekman Dynamics

海洋锋、俯冲和自旋：非线性埃克曼动力学

• 批准号: 0351191
• 负责人: Peter Rhines
• 金额: $ 38.79万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-02-01 至 2007-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0351191&HistoricalAwards=false
• 关键词: Oceanic; Fronts; Subduction; Spin; up

ABSTRACTOCE-0351191This study involves theory, modeling and observational work related to the forcing of theupper ocean by atmospheric winds and buoyancy flux. The PI and his team have found a new mechanism for the generation of fronts in a wind-driven ocean, using nonlinear theory. Atmospheric forcing by wind-stress and surface buoyancy flux drives the ocean through direct cooling, cooling augmented by horizontal heat transport in the upper Ekman layer, and divergence of the Ekman-layer volume transport modified by vertical vorticity. The latter two forcing effects are a consequence of nonlinear Ekman dynamics. Using a convection parameterization, the two-dimensional sub-inertial response of the subsurface ocean is predicted: it involves spontaneous development of fronts, downwelling at these fronts, buoyant convection at special sites related to the fronts, and the spin-up of downwind currents in a pattern that is highly structured by frontal downwelling. The potential vorticity field, q, acts as a key control; changes in the sign of q enable spin-up and instability to take on distinctive forms. q changes sign when surfaces of constant density slope more steeply than absolute momentum surfaces. Non-hydrostatic numerical simulations verify these results. The present study will start from this basis and emphasize three aspects of the ocean circulation: (i) generation of density- and velocity- fronts by strong wind fields in a fully three dimensional ocean; (ii) spin-up of circulation within and beneath the oceanic upper mixed layer, and (iii), amplification and forced propagation of anticyclonic circulation and eddies in the upper ocean by large-scale winds. Both 3- dimensional modeling and observations will be used. Model studies involve process oriented simulations aimed at understanding in the context of nonlinear Ekman dynamics, the preferential generation of anticyclones by wind-jets, propagation of wind-forced eddies by Ekman-pumping-induced vortex stretching, and evolution of wind-forced boundary currents in a Labrador Sea-like basin. Another goal is to use the theory to guide hydrostatic ocean circulation models so that they are able to capture the dynamics of wind-driven frontogenesis and frontal downwelling. Particular observational data-sets to be used include high-resolution satellite scatterometer wind-fields from Labrador Sea and subpolar fronts of the Atlantic, high-resolution sea-soar and ADCP data from the subpolar front of the Japan/East Sea, and high-resolution ctd sections taken with the Eriksen Seaglider. Sea-soar/ADCP surveys are now a commonplace tool used in frontal/mesoscale studies. The proposed work develops an inverse method to use such surveys with the theory above to both estimate ageostrophic overturning circulation and partition its driving force into contributions from wind, cooling, and confluent/diffluent geostrophic flow.Broader Impacts. Beyond physical science, this work relates particularly closely toecosystems living near ocean fronts, in upwelling regions at coasts or along the Equator: regions which are particularly stressed by global change. In this way it contributes to understanding of Earth's habitability. This research also contributes to the PI's undergraduate teaching in environmental studies, in which the methods and results of science are put before young students who are the beneficiaries and custodians of the environment. It also motivates public lecturing on the environment.

Abstractoce-0351191这项研究涉及与大气风和浮力助理相关的理论，建模和观察性工作。 PI和他的团队使用非线性理论找到了一种新的机制，用于在风向海洋中产生前线。大气压力和表面浮力通量强迫通过直接冷却来驱动海洋，在上埃克曼层中的水平热传输增强，并通过垂直涡度修饰的Ekman-Layer体积传输的发散。后两个强迫效应是非线性Ekman动力学的结果。使用对流参数化，可以预测地下海洋的二维亚惯性响应：它涉及前部的自发发展，在这些方面的偏低，在与前部相关的特殊地点的浮力对流，以及以一种由Frontal Downlisterlisterlisterling构造的下风电流的旋转模式。潜在的涡度场Q充当关键控制； Q的迹象的变化使旋转和不稳定性能够采用独特的形式。当恒定密​​度斜率的表面比绝对动量表面更陡峭时，Q会改变标志。非静态数值模拟验证了这些结果。本研究将从此基础开始，并强调海洋循环的三个方面：（i）在完全三维的海洋中，强风场产生密度和速度 - 前沿； （ii）在海洋上部混合层内部和下方的循环旋转，以及（iii），通过大规模风在上海中的反气旋循环和涡流强迫传播。将使用三维建模和观察结果。模型研究涉及旨在在非线性Ekman动力学的背景下进行理解的过程模拟，这是风流的优先生成反气旋，通过Ekman-Pumping诱导的涡流拉伸的风力涡流传播，以及在Labrador Sea Like Like Like Like Like Basin中的风力范围的进化。另一个目标是使用该理论指导静液压海洋循环模型，以便他们能够捕获风驱动的额叶生成和额叶下降的动力学。 要使用的特定观察性数据集包括来自拉布拉多海的高分辨率卫星散射仪和大西洋的亚极前线，日本/东海的亚极前面的高分辨率海上和ADCP数据，以及高分辨率的CTD阶层。 SEA-SOAR/ADCP调查现在是额叶/中尺度研究中使用的常见工具。提出的工作开发了一种与上述理论一起使用此类调查的反相反方法，以估计循环的年龄，并将其驱动力划分为风，冷却和融合/汇合/散布的地质流动的贡献。除了物理科学之外，这项工作还特别紧密地关联了生活在海洋阵线附近，海岸上升地区或赤道沿岸的临时系统：全球变化特别强调的地区。通过这种方式，它有助于理解地球的可居住性。这项研究还为PI在环境研究中的本科教学做出了贡献，在该研究中，科学的方法和结果是在受益人和环境监护人的年轻学生面前。它还激发了公众在环境上的讲座。