Collaborative Research: Equatorial Internal Gravity Wave Shear, Strain, Instabilities and Mixing--A Moored Process Study

合作研究：赤道内重力波剪切、应变、不稳定性和混合——停泊过程研究

• 批准号: 0728375
• 负责人: James Moum
• 金额: $ 48.74万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-08-15 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0728375&HistoricalAwards=false
• 关键词: Collaborative; Research; Equatorial; Internal; Gravity

Understanding the physics of instabilities that lead to the unique strong turbulent flux below the equatorial cold tongue is an imperative step toward developing a physics-based turbulence parameterization for improving the model prediction of the El Nino-Southern Oscillation (ENSO) phenomenon. The primary goal of this experiment is to make long-term observations of detailed evolutions of internal waves, instabilities, and mixing at time scales from 1-min to months and at vertical scales from 0.5 m to O(100) m below the equatorial cold tongue. The tongue of cold water straddling the equator in the eastern Pacific is one of the major sea surface temperature (SST) features influencing tropical air-sea interactions. Vertical turbulent fluxes through the base of the surface mixed layer are major factors in the heat budget that determines SST. Strong turbulence during La Nina cools the mixed layer, strengthening the cold tongue. Weak turbulence during El Nin1 allows the mixed layer to warm, weakening or erasing the cold tongue. Several periods of intensive microstructure profiling discovered the role of small-scale mixing in modulating the cold tongue, but attempts to parameterize the turbulent fluxes failed because the physics leading to instabilities and turbulence has not been captured by these measurements. Previous observations indicate that internal waves play the key role by providing the finescale shear that trigger instabilities. High spatial and temporal resolutions of measurements, sufficiently capturing instabilities below the cold tongue, are needed, but have not been made.In the present experiment, shear and strain will be measured at 1-minute intervals over vertical scales of O (1-100) m and turbulent scalar diffusion rates immediately beneath the surface mixed layer in the cold tongue. Co-investigators Moum and Nash at OSU have recently developed a moored microstructure package that can reliably measure turbulent scalar diffusion rates in the equatorial undercurrent. Closely vertically spaced instruments measuring velocity, temperature, salinity and mixing rates will be mounted on a surface mooring. The mooring will be 5 miles from the long-term TAO mooring at 0 140 W. The experiment will be coordinated with another funded observational program. In spring 2008, 10 pods, evenly spaced between 30 and 90-m depth, will be deployed on the long-term TAO mooring at 0 140 W. The deployment will be Immediately with18 days of shipboard microstructure profiler measurements. Intellectual Merit.Internal waves produce much of the diapycnal mixing in the ocean and must be understood and quantified before accurate mixing parameterizations can be developed. In the eastern equatorial Pacific, the stratified high-shear zone between the undercurrent core and the base of the mixed layer provides a unique environment for internal waves. Understanding it well enough to accurately parameterize the diapycnal mixing is a major intellectual challenge whose solution will advance the general understanding of internal waves, instabilities, and turbulence, as well as provide necessary support for climate studies.Broader ImpactThis work is expected to lead to more accurate parameterizations of equatorial mixing in general circulation models (GCM) and thus to more realistic climate models. SST, air-sea interaction, and ENSO in the cold tongue are strongly controlled by the turbulence entrainment flux. To improve the large-scale model prediction of ENSO, we need to understand the physics of instabilities and turbulence and improve the turbulence parameterization in GCMs. The proposed project will provide support for the education of a graduate student. The observations and analysis results will be published on a publicly accessible website.

了解导致赤道冷舌下方独特的强湍流通量的不稳定性的物理学是朝着开发基于物理学的湍流参数化以改进厄尔尼诺-南方涛动（ENSO）现象的模型预测迈出的必要一步。该实验的主要目的是在赤道冷舌以下0.5 m至O（100）m的时间尺度上对内波、不稳定性和混合的详细演变进行长期观测。东太平洋横跨赤道的冷水舌是影响热带海气相互作用的主要海表温度特征之一。通过地面混合层底部的垂直湍流通量是决定SST的热量收支的主要因素。拉尼娜期间的强烈湍流冷却了混合层，加强了冷舌。厄尔尼诺现象期间的弱湍流使混合层变暖，削弱或消除冷舌。几个时期的密集的微观结构剖析发现的作用，小规模的混合调制冷舌，但试图参数化的湍流通量失败，因为物理导致的不稳定性和湍流还没有被这些测量捕获。以前的观测表明，内波通过提供触发不稳定性的细尺度剪切而起着关键作用。高的空间和时间分辨率的测量，充分捕捉冷舌下的不稳定性，是必要的，但还没有made.在本实验中，剪切和应变将在1分钟的时间间隔测量垂直尺度为O（1-100）m和湍流标量扩散率直接在冷舌的表面混合层下面。俄勒冈州立大学的合作研究者Moum和Nash最近开发了一种停泊的微结构包，可以可靠地测量赤道暗流中的湍流标量扩散速率。测量流速、温度、盐度和混合率的垂直间隔很近的仪器将安装在水面系泊设备上。系泊距离0140 W处的长期TAO系泊5英里。该实验将与另一个资助的观测计划协调。2008年春季，将在0140 W的长期TAO系泊上部署10个吊舱，平均间隔在30 - 90 m深度之间。部署将立即与18天的船上微观结构剖面测量。知识价值：内波产生了海洋中的大部分贯向混合，在发展精确的混合参数化之前，必须对内波进行理解和量化。在赤道东太平洋，潜流核心和混合层底部之间的分层高切变带为内波提供了独特的环境。了解它足够好，准确地parameterized的diapycnal混合是一个重大的智力挑战，其解决方案将推进内波，不稳定性和湍流的一般理解，以及提供必要的支持气候studies.Broader ImpactThis工作预计将导致更准确的参数化赤道混合在大气环流模式（GCM），从而更现实的气候模式。冷舌区的SST、海气相互作用和ENSO都受湍流卷吸通量的强烈控制。为了改进ENSO的大尺度模式预测，我们需要了解不稳定性和湍流的物理学，并改进GCM中的湍流参数化。拟议的项目将为一名研究生的教育提供支助。观察和分析结果将公布在一个可供公众查阅的网站上。