Instability and Turbulence in a Sheared, Diffusively Unstable Fluid

[0453140]地球海洋中热量的混合、输送和封存是我们目前对气候系统认识的一个主要不确定因素。双扩散不稳定性是指一组在大气中没有类似物的混合过程，它们的存在在1960年以前是没有人怀疑的。在海水中热量和盐的分子扩散率的巨大差异的驱动下，这些过程对海洋混合做出了重大贡献。在最简单的模型中，双重扩散采取两种形式之一：盐指化和扩散分层，这两种形式在世界海洋的许多地区形成易于识别的温盐阶梯结构。盐指化现象在中纬度水域很常见，而扩散分层现象在两极附近更为突出。这种剪切/双扩散相互作用的理论研究将阐明在受剪切和双扩散不稳定影响的海洋内部大片区域中活跃的混合机制。该研究将采用一次和二次稳定性分析和直接数值模拟相结合的方法。这些将集中在弯曲剪切流（有或没有惯性旋转）和有利于指状的分层。更广泛的影响：除了对这一海洋学上重要的分层湍流机制提供新的物理见解外，这项工作还将改进湍动通量的参数化和各向异性统计，用于观测数据分析和大规模建模。拟议的工作将改善大尺度海洋和气候模式中小尺度通量的代表性，从而解决可靠气候预报的主要障碍之一，从而使社会受益。该项目将为一名科学程序员提供部分支持，并为一名研究生提供全部支持，该研究生将学习海洋混合理论研究的最新技术。这项研究将与埃里克教授合作进行。加拿大维多利亚大学的Kunze说。

0453140Mixing, transport and sequestration of heat in the Earth's oceans contributes a major element of uncertainty to our present understanding of the climate system. Double diffusive instability refers to a set of mixing processes that have no analogue in the atmosphere and whose existence was unsuspected before 1960. Driven by the vast difference in the molecular diffusivities of heat and salt in seawater, these processes contribute significantly to ocean mixing. In the simplest model, double diffusion takes one of two forms: salt fingering and diffusive layering, both of which form easily recognizable thermohaline staircase structures in many regions of the world ocean. Salt fingering is common in mid-latitude waters, while diffusive layering is more prominent near the poles. This theoretical study of shear / double diffusion interactions will illuminate mixing mechanisms active in the large regions of the ocean interior that are subject to both shear and double diffusive instability. The research will employ a combination of primary and secondary stability analyses and direct numerical simulations. These will focus on inflectional shear flows (with and without inertial rotation) and fingering-favorable stratification. Broader Impacts: Besides furnishing new physical insights into this oceanographically important regime of stratified turbulence, the work will result in improved parameterizations of diapycnal fluxes and anisotropy statistics for use both in the analysis of observational data and in large-scale modeling. The proposed work will benefit society by improving the representation of small-scale fluxes in large-scale ocean and climate models, thereby addressing one of the main obstacles to reliable climate forecasting. The project will provide partial support for a scientific programmer and full support for a graduate student, who will learn the latest techniques for the theoretical study of ocean mixing. The research will be done in collaboration with Professor Eric. Kunze of the University of Victoria, Canada.