Kelvin-Helmholtz turbulence: how much mixing does it generate in the Equatorial Oceans?

开尔文-亥姆霍兹(KH)不稳定是剪切不稳定最简单的形式，也是海洋中最常见的混合机制。尽管它无处不在，但关于KH不稳定性及其产生的湍流仍有许多未知之处，包括决定混合量的根本问题。有两个限制限制了我们回答这个问题的能力。首先，许多已知的信息来自实验室实验和直接数值模拟(DNS)，其规模小于海洋的典型尺度。其次，由于所需测量的高分辨率，观测是稀疏的。近年来，这两个限制都有所放松。PETSCALE计算现在提供了在雷诺数大大增加的情况下执行DNS的机会，而通过温度耗散吊舱引入长期的系泊测量提供了扩展的记录，既可以识别KH湍流，又可以量化所产生的混合。总体而言，该项目将提高我们对一类重要的海洋混合过程的理解，提供用于观测数据分析和最终气候预报的新参数，并补充正在进行的由美国国家科学基金会资助的层状切变流混合研究。现有的海洋域名系统代码将升级并分发给社区使用，一名受过湍流理论和数值模拟培训的博士后科学家将接受观测技术和数据分析方面的培训，并有机会参与海洋研究。该项目的主要目标是记录湍流Kelvin-Helmholtz波流的混合特性，导致净湍流通量的参数化。新的数值模拟系统将与现有和正在进行的测量相结合，以了解与海洋混合有关的湍流统计数据如何随着雷诺数的增加而变化，并预测混合事件中释放的能量、耗散率和有效扩散率。结果将被用来创造赤道太平洋混合的数十年记录，并将作为应用于大西洋和所有近临界层状切变流的模式。

Kelvin-Helmholtz (KH) instability is the simplest form of shear instability, and is arguably the most common mechanism for mixing in the oceans. Despite its ubiquity, much remains unknown about KH instability and the turbulence it generates, including the fundamental question of what determines the amount of mixing accomplished. Two constraints limit our ability to answer this question. First, much of what is known comes from lab experiments and direct numerical simulations (DNS) at scales smaller than are typical of the ocean. Second, observations are sparse due to the high resolution of the required measurements. In recent years both of these constraints have been relaxed. Petascale computing now offers the opportunity to execute DNS at greatly increased Reynolds number, while the introduction of long-term, moored measurements via temperature dissipation pods provides extended records that both identify KH turbulence and quantify the resultant mixing. Overall, this project will improve our understanding of an important class of ocean mixing processes, deliver new parameterizations for use in observational data analysis and, ultimately, climate forecasts, and complement ongoing NSF-funded studies of mixing in stratified shear flows. An existing Ocean DNS code will be upgraded and distributed for community use, and a postdoctoral scientist schooled in turbulence theory and numerical simulation will be trained in observational techniques and data analysis and provided with the opportunity to take part in seagoing research.The main objective of this project is to document the mixing properties of turbulent Kelvin-Helmholtz billows, leading to parameterizations of the net turbulent fluxes. New DNS will be used in combination with existing and ongoing measurements to learn how turbulence statistics relevant to ocean mixing change as the Reynolds number is increased, and to predict the energy released in a mixing event, the dissipation rate, and the effective diffusivity. The results will be used to create a multi-decade record of mixing in the equatorial Pacific, and will serve as a model for application to the Atlantic and to all near-critical stratified shear flows.