Parameterizations of Salt Fingers in the Ocean

海洋盐指的参数化

• 批准号: 1433132
• 负责人: Raymond Schmitt
• 金额: $ 58.59万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2019-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1433132&HistoricalAwards=false
• 关键词: Parameterizations; Salt; Fingers; Ocean

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.

这项研究的最终目标是增进我们对海洋中盐指双重扩散的理解，以便能够正确解释现场观测，并开发这种现象的新表示，以纳入大规模海洋环流模型。盐指作用是一种发生在热带和亚热带地区的海洋混合过程，这些地区的温暖和咸水覆盖着较冷和较新鲜的水。这是因为，在水中，热量的扩散速度比盐快。一小块温暖的咸水向下沉入较冷、较新鲜的区域，在失去盐分之前会失去热量，使这块水比周围的水密度更大，并进一步下沉。同样，一小部分较冷、较新鲜的水将向上移动，并通过从周围的水扩散而获得热量，从而使其比周围的水轻，并导致其进一步上升。与深渊中的湍流混合相比，盐指存在的位置可能会增强海洋吸收和输送热量、淡水和营养物质的能力。因此，开发量化盐指通量所需的工具非常重要。现在有相当丰富的证据表明，盐指强度是密度比的强函数，并且可以反馈海洋的分层。该项目旨在以新的理论结果和高质量的数据集为基础，更好地量化海洋中盐指引起的混合，并加快海洋环流数值模型的合理表示的进展，该模型对双扩散具有明显的敏感性。该项目还将有助于增进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不同领域都很重要。研究人员计划参加 2015 年拟议的“层与界面数学”多学科研讨会。该项目还将为参与该项目的伍兹霍尔海洋研究所本科暑期学生研究员的教育发展做出贡献作为他们夏季研究项目的一部分。该项目中的许多优秀学生后来都成为非常成功的研究生。精细结构、微观结构和示踪剂数据的分析将与理论分析和数值模拟一起进行，以便更好地了解盐指在海洋混合中的作用。现在，盐指重要性的证据已经很清楚了。它是某些地区占主导地位的温跃层混合过程，也是许多其他地区的重要贡献者。热量和盐以不同的速率传输这一事实对温盐结构和海洋动力学产生了多种影响。该项目有四个主要要素。首先，将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来开发盐指参数化，以测试与新盐指平衡模型的一致性。其次，将使用Moered Profiler 时间序列数据分析SFTRE 温盐阶梯的特性。 Theta-S 空间中的层特性分析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层形成和厚度模型，这些模型依赖于随着密度比的增加而减小的指通量比。第三，将使用示踪剂数据结合各层非常一致的 Theta-S 特性，对楼梯中的剪切分散和横向混合进行研究。这将在该区域的整体经向梯度内定位任何一层观测，并允许研究人员确定有意示踪剂的横向分散。这一分析将允许评估各层相对于彼此的位移，并改进垂直和横向扩散率的估计。第四，将对不稳定分层中的手指进行分析。理论和数值模型将用于帮助理解基于最近实验结果的新参数体系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态的大气环流模型，这两项任务对社会非常重要。