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What can fine-scale stratification structure in thermal microscale profiles of lakes tell us about their turbulence history?

湖泊热微尺度剖面中的精细分层结构可以告诉我们什么关于它们的湍流历史？

基本信息

批准号：
NE/G010498/1
负责人：
Andrew Folkard
金额：
$ 6.47万
依托单位：
Lancaster University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2009
资助国家：
英国
起止时间：
2009 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG010498%2F1
关键词：
What fine scale stratification structure

项目摘要

Turbulent mixing in density-stratified fluids is of central importance to the cycling of heat, and key biogeochemical elements from global to micro-scales, and thus to the climate and ecosystems of our planet. Despite this, a recent review by three world-leaders in the field of environmental turbulence [Ivey et al 2008] emphasises that our sampling of this phenomenon 'does not begin to approach' a reliable representation of its magnitude or spatio-temporal structure. As a result, there remain very large, untested areas of our understanding of problems ranging from the global-scale cycling of heat in the oceans, to the patterns of nutrient cycling in small lakes. This problem is so persistent because of the highly variable nature of turbulence, and the fact that current instrumentation can only measure it at a very limited number of points for any significant time, or for a short time (a quasi-instantaneous snapshot) at any significant number of points. The aim of this project is to investigate whether existing turbulence profile data can provide us with a detailed and reliable history of turbulent activity and thus allow us to expand the extent to which we can sample it. The approach focuses on the apparently ubiquitous (and hitherto not analysed) presence of small-scale layering that is revealed in micro-scale temperature profiles of thermally-stratified water bodies. While some (e.g. MacIntyre, pers. comm.) argue that they are caused by internal wave motions which locally squash and stretch the isotherms, thus distorting vertical temperature profiles, there is also the strong possibility that at least some are the result of local turbulent mixing. The current approach to analysing microstructure profiles for turbulence data considers only the evidence of active turbulence within the profile. It either identifies statistically stationary segments, from which it determines measures of vertical turbulent diffusivity, or it identifies turbulent patches. This project will compare the turbulence distributions identified through those methods with the fine-scale stratification structure. From this, relationships will be identified between measures of turbulent overturn characteristics and the underlying stratification, and distinctions made between regions of fine-scale stratification structure which are actively turbulent and those which are not. We will test the hypothesis that we can use the former to develop stratification-turbulence relationships that would allow use of the fine-scale stratification data as a proxy for turbulent activity, and then apply that relationship to the latter to quantify the historical turbulent activity evidenced in these footprints of now-decayed turbulence. We hypothesise further that this would, at least, give us an upper limit on the historical turbulence intensity (i.e. it would assume that all the fine-scale stratification structure was caused by now-decayed turbulence), and would provide pump-priming for further investigation of this phenomenon that would (a) investigate ways of distinguishing turbulence footprints from internal wave footprints; and (b) compare this physical fine scale structure with that in chemical and biological parameters and allow us to infer its biogeochemical and ecological relevance. The project addresses an issue - turbulent mixing - that is central to biogeochemical and thermal cycling in lakes, and thus efforts to enhance the quality of lakes and research into the role of lakes in global nutrient cycles and climate change.

密度分层流体中的湍流混合对热量循环和从全球到微观尺度的关键地球化学元素，从而对我们星球的气候和生态系统至关重要。尽管如此，环境湍流领域的三位世界领导人最近的一篇评论[Ivey et al 2008]强调，我们对这种现象的采样“并没有开始接近”其量级或时空结构的可靠表示。因此，我们对问题的理解仍然有很大的未经检验的领域，从全球范围的海洋热量循环到小湖泊的营养循环模式。这个问题是如此持久，因为湍流的高度可变的性质，以及目前的仪器只能在非常有限的数量的点上测量任何重要的时间，或在短时间内（准瞬时快照）在任何重要的数量的点。该项目的目的是调查现有的湍流廓线数据是否可以为我们提供一个详细和可靠的历史湍流活动，从而使我们能够扩大到我们可以采样it. The方法的程度上显然无处不在（迄今尚未分析）存在的小尺度分层，揭示在微尺度温度廓线的热分层水体。虽然有些人（例如麦金太尔，pers. comm.）虽然有学者认为它们是由内部波动引起的，内部波动局部挤压和拉伸等温线，从而扭曲了垂直温度分布，但也有很大的可能性，至少有一些是局部湍流混合的结果。目前分析湍流数据的微结构剖面的方法只考虑剖面内活跃湍流的证据。它可以识别统计上稳定的片段，从它确定垂直湍流扩散率的措施，或者它确定湍流补丁。本项目将比较通过这些方法确定的湍流分布与细尺度分层结构。从这一点，将确定湍流翻转特性的措施和底层分层之间的关系，并区分区域之间的细尺度分层结构，积极动荡和那些不是。我们将测试的假设，我们可以使用前者开发分层湍流的关系，将允许使用的细尺度分层数据作为湍流活动的代理，然后将这种关系应用到后者，以量化的历史湍流活动证明在这些足迹现在衰变的湍流。我们进一步假设，这至少会给我们一个历史湍流强度的上限（即，它将假设所有的精细尺度分层结构是由现在衰减的湍流引起的），并将为进一步研究这种现象提供泵启动，这将（a）研究区分湍流足迹和内波足迹的方法;（B）将这一物理精细尺度结构与化学和生物参数中的精细尺度结构进行比较，并使我们能够推断其地球化学和生态相关性。该项目解决了一个问题-湍流混合-这是湖泊地球化学和热循环的核心，因此努力提高湖泊的质量和研究湖泊在全球养分循环和气候变化中的作用。