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

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学是发展基于物理的湍流参数化以改进厄尔尼诺-南方涛动（ENSO）现象的模式预测的必要步骤。本实验的主要目标是在1分钟到1个月的时间尺度上，以及在赤道冷舌以下0.5米到100米的垂直尺度上，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温特征之一。通过地表混合层底部的垂直湍流通量是决定海温的热收支的主要因素。拉尼娜期间强烈的湍流冷却了混合层，加强了冷舌。厄尔尼诺现象期间的弱湍流使混合层变暖，削弱或抹去了冷舌。几次密集的微观结构分析发现了小尺度混合在调节冷舌中的作用，但试图参数化湍流通量的尝试失败了，因为这些测量没有捕捉到导致不稳定和湍流的物理现象。先前的观察表明，内波通过提供触发不稳定的细尺度剪切起关键作用。需要高空间和时间分辨率的测量，以充分捕捉冷舌以下的不稳定性，但尚未实现。在本实验中，将在0 (1-100)m的垂直尺度上每隔1分钟测量一次剪切和应变，并在冷舌表面混合层下方测量湍流标量扩散率。俄勒冈州立大学的合作研究者Moum和Nash最近开发了一种系泊微结构包，可以可靠地测量赤道潜流中的湍流标量扩散速率。测量速度、温度、盐度和混合率的紧密垂直间隔仪器将安装在地面系泊上。系泊将在距离长期TAO系泊5英里处，在0140瓦。该实验将与另一个资助的观测项目协调。2008年春季，10个吊舱将均匀分布在30米至90米深度之间，部署在140瓦的长期TAO系泊上。部署后将立即进行为期18天的船载微观结构剖面仪测量。知识价值。在海洋中，内波产生了大量的潜流混合，必须先对其进行理解和量化，然后才能发展出精确的混合参数化。在赤道东太平洋，暗流核心与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。充分了解它以准确地参数化底波混合是一项重大的智力挑战，其解决方案将促进对内波、不稳定性和湍流的一般理解，并为气候研究提供必要的支持。更广泛的影响这项工作预计将导致在一般环流模式（GCM）中更精确地参数化赤道混合，从而产生更现实的气候模式。冷舌海温、海气相互作用和ENSO受湍流夹带通量的强烈控制。为了提高ENSO的大尺度模式预测，我们需要了解不稳定和湍流的物理特性，并改进gcm中的湍流参数化。建议的项目将为研究生的教育提供支持。观察和分析结果将在一个公众可访问的网站上公布。

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.