Parameterizations of Salt Fingers in the Ocean

本研究的最终目标是促进我们对海洋中盐指双扩散的理解，以便能够正确解释现场观测结果，并开发这种现象的新表示，以便纳入大尺度海洋环流模式。盐指化是一种海洋混合过程，发生在热带和亚热带地区，温暖和咸水覆盖在寒冷和淡水上。这是因为在水中，热量比盐扩散得快。一小块温暖的咸水下沉到更冷、更新鲜的地区，会在失去盐分之前失去热量，使这一小块水比周围的水密度越来越大，并进一步下沉。同样，一小部分较冷、较新鲜的水将向上移动，并通过周围水的扩散获得热量，这将使它比周围的水轻，并导致它进一步上升。与深渊中的湍流混合相比，存在盐指的地方可能会增加海洋吸收和运输热量、淡水和营养物质的能力。因此，开发量化盐指通量的必要工具是非常重要的。盐指强度是密度比的强函数，并能反馈海洋分层的证据现在相当丰富。该项目旨在建立在新的理论结果和高质量数据集的基础上，以更好地量化海洋中盐指引起的混合，并加快在海洋环流数值模型中合理表示的进展，这些模型已证明对双重扩散具有敏感性。该项目还将有助于提高双扩散系统的一般知识，双扩散系统现在被认为在天体物理学和岩浆等各种领域都很重要。研究者计划在2015年参加一个关于“层和界面的数学”的多学科研讨会。该项目还将促进伍兹霍尔海洋研究所本科生暑期学生研究员的教育发展，他们将参与该项目，作为其暑期研究项目的一部分。这个项目的许多优秀学生后来都成为了非常成功的研究生。为了更好地理解盐指在海洋混合中的作用，将对细结构、微观结构和示踪数据进行分析，同时进行理论分析和数值模拟。“盐指”重要性的证据现在已经很清楚了；它是某些地区主要的温跃层混合过程，也是许多其他地区的重要贡献者。热量和盐以不同速率传输的事实对热盐结构和海洋动力学有各种各样的影响。这个项目有四个主要元素。首先，使用盐指示踪剂释放实验（SFTRE）以及其他巡航的微观结构数据进行盐指参数化，以测试新的盐指平衡模型的一致性。其次，将使用Moored Profiler时间序列数据分析stre温盐阶梯的性质。分析Theta-S空间中的层性质将用于评估现有通量散度模型的可行性。此外，该分析将有助于测试依赖于手指通量比随密度比增加而减小的层形成和厚度模型。第三，将利用示踪剂数据结合各层显著一致的Theta-S特性，对阶梯中的剪切分散和横向混合进行研究。这将在该地区的整个子午梯度内定位任何一层观测，并允许研究者建立故意示踪剂的横向分散。这种分析将允许评估相对于其他层的位移，并改进垂直和横向扩散系数的估计。第四，对不稳定分层中的手指进行分析。理论和数值模拟将用于帮助理解基于最近实验结果的新参数制度如何有可能影响海洋中的“混合”层分层。总体而言，该项目将有助于改进用于气候预测和生态系统动力学的环流模式，这两项任务对社会都具有重要意义。

The ultimate goal of this research is to advance our understanding of double diffusion from salt fingers in the ocean so that field observations can be properly interpreted and new representations of this phenomenon can be developed for inclusion in large-scale ocean circulation models. Salt fingering is an ocean mixing process that occurs in tropical and sub-tropical regions where warm and salty water overlies colder and fresher water. It is driven by the fact that, in water, heat diffuses faster than salt. A small parcel of warm, salty water sinking downwards into a colder, fresher region will lose its heat before losing its salt, making the parcel of water increasingly denser than the water around it and sinking further. Likewise, a small parcel of colder, fresher water will be displaced upwards and gain heat by diffusion from surrounding water, which will then make it lighter than the surrounding waters, and cause it to rise further. Locations where salt fingers are present may increase the ability of the oceans to absorb and transport heat, freshwater and nutrients than turbulent mixing in the abyss. Thus, it is very important to develop the tools necessary to quantify salt finger fluxes. The evidence that salt finger intensity is a strong function of density ratio and can feedback on the ocean's stratification is now quite abundant. This project aims to build on new theoretical results and high quality data sets to better quantify the mixing due to salt fingers in the ocean and hasten the progress toward a plausible representation in numerical models of the ocean circulation, which have a demonstrated sensitivity to double diffusion. This project will also contribute to the general knowledge of double-diffusive systems which are now recognized to be important in fields as diverse as astrophysics and magmas. The investigator plans to participate in a proposed multi-disciplinary workshop on "The Mathematics of Layers and Interfaces" in 2015. The project will also contribute to the educational development of undergraduate Summer Student Fellows at the Woods Hole Oceanographic Institution who will participate in the project as part of their summer research projects. Many of the excellent students in that program go on to become very successful graduate students.Analysis of finestructure, microstructure and tracer data will conducted along with theoretical analysis and numerical simulations in order to better understand the role of salt fingers in oceanic mixing. Evidence for the importance of salt fingers is now clear; it is the dominant thermocline mixing process in some regions and a significant contributor in many others. The fact that heat and salt are transported at different rates has a variety of consequences for thermohaline structure and ocean dynamics. There are four main elements to this project. First, a parameterization of salt fingers using microstructure data from the Salt Finger Tracer Release Experiment (SFTRE) as well as other cruises will be developed to test consistency with the new salt finger equilibration model. Second, the properties of the SFTRE thermohaline staircase will be analyzed using the Moored Profiler time series data. The analysis of layer properties in Theta-S space will be used to evaluate the viability of an existing flux divergence model. In addition, this analysis will help test the layer formation and thickness models which rely on a decreasing finger flux ratio with increasing density ratio. Third, a study of shear dispersion and lateral mixing in the staircase will be conducted using the tracer data in conjunction with the remarkably consistent Theta-S properties of the layers. This will locate any one layer observation within the overall meridional gradients of the region and permit the investigator to establish the lateral dispersion of the deliberate tracer. This analysis will allow the assessment of the displacement of layers relative to one another, and improve estimates of both vertical and lateral diffusivities. Fourth, an analysis of fingers in unstable stratifications will be done. Theory and numerical modeling will be used to help understand how a new parameter regime based on recent experimental results has the potential to affect "mixed" layer stratifications in the ocean. Overall, this project will contribute to improvement of the general circulation models used for climate prediction and ecosystem dynamics, both tasks of great importance to society.