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

为了提高厄尔尼诺-南方涛动(ENSO)现象的模式预报，了解导致赤道冷舌下独特的强湍流通量的不稳定性的物理机制是发展基于物理的湍流参数化的必要步骤。本实验的主要目的是对赤道冷舌下1分钟到数月的时间尺度和0.5米到O(100)米的垂直尺度的内波、不稳定性和混合的详细演变进行长期观测。横跨东太平洋赤道的冷水舌是影响热带海-气相互作用的主要海面温度特征之一。通过地面混合层底部的垂直湍流通量是决定海温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，加强了寒冷的舌头。厄尔尼诺期间的微弱湍流使混合层变暖，减弱或抹去冰冷的舌头。几个时期的密集微结构剖析发现了小尺度混合在调节冷舌方面的作用，但尝试对湍流通量进行参数化的尝试失败了，因为这些测量没有捕捉到导致不稳定性和湍流的物理过程。先前的观测表明，内波通过提供触发不稳定的细尺度切变而发挥关键作用。需要高的空间和时间分辨率的测量，以充分捕捉冷舌下的不稳定。在本实验中，将在O(1-100)m的垂直尺度和紧接在冷舌表面混合层下方的湍流标量扩散速率上以1分钟的间隔测量切变和应变。俄亥俄州立大学的合作研究人员穆姆和纳什最近开发了一种系泊微结构组件，可以可靠地测量赤道暗流中的湍流标量扩散速率。测量速度、温度、盐度和混合率的垂直距离很近的仪器将安装在水面系泊设备上。系泊距离长期的TAO系泊在0140W处5英里。该实验将与另一个资助的观测项目协调进行。2008年春季，10个吊舱将均匀分布在深度30至90米之间，部署在0140 W的长期TAO系泊设备上。部署后将立即进行为期18天的船上微结构剖面仪测量。智力价值。内波在海洋中产生了大量的昼夜混合，在开发准确的混合参数之前，必须了解和量化内波。在赤道东太平洋，潜流核心和混合层底部之间的层状高剪切带为内波提供了独特的环境。充分理解它以准确地将赤道混合参数化是一项重大的智力挑战，其解决方案将促进对内波、不稳定和湍流的一般理解，并为气候研究提供必要的支持。广泛的影响这项工作有望导致在大气环流模式(GCM)中更准确地对赤道混合进行参数化，从而产生更现实的气候模式。海温、海气相互作用和冷舌中的ENSO受湍流卷吸通量的强烈控制。为了提高ENSO的大尺度模式预报水平，我们需要了解不稳定和湍流的物理机制，并改进GCMS中的湍流参数化。拟议的项目将为研究生的教育提供支持。观察结果和分析结果将在一个可公开访问的网站上公布。

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.