Routes to vertical mixing in the Equatorial Under Current: quantification through high-resolution numerical simulations

知识价值：理解和量化热带太平洋赤道潜流（EUC）系统的热量和动量垂直通量是将流动不稳定性和湍流混合的小尺度物理与ENSO等大尺度气候变率联系起来的核心问题之一。在过去二十年中取得了重大进展，主要是由于同时观测平均和湍流垂直剖面并结合经典线性稳定性分析。然而，重大的不确定性仍然存在，特别是，在背景切变线性稳定的深度，高频内波和相干湍流斑块的独特混合是如何开始和持续的机制，人们知之甚少。在这个项目中，将进行高分辨率的数值研究，以量化能量来源-地面风，浮力通量和射流的平均动能-进入湍流耗散的途径。该项目改进的建模能力主要基于高分辨率LES，将补充正在进行的观测项目。这些在大型NSF计算设备上进行的三维非流体静力模拟将直接解决导致湍流和垂直通量的流动不稳定性。时空数据集的分析将集中于阐明在背景条件线性稳定的区域中负责维持湍流的有限振幅非线性机制。模拟将以切变和分层背景剖面的形式结合新的观测结果，并结合相应的风应力和热通量。这项工作的主要目标是了解在各种条件下EUC中湍流产生和输运的物理机制，并量化相关的能量输运和垂直通量。更广泛的影响：在科学上，所提出的努力将有助于发展基于物理的参数化和广泛的社会利益的预测能力。该项目将直接支持培养一名越南裔博士后学者，这是一个在科学界代表性不足的群体。它将通过与现有的国家科学基金会资助的关于计算流体动力学模拟数据库设计的项目合作，促进计算和信息技术基础设施的发展。该项目还将直接支持加州大学圣地亚哥分校的研究生教育，将分析和数值技术和结果纳入现有的环境和计算流体动力学课程，这些课程在加州大学圣地亚哥分校的机械和航空航天工程以及斯克里普斯海洋学研究所交叉列出。PI团队的跨学科性质将确保在地球科学和工程界广泛传播结果。

Intellectual Merit: Understanding and quantifying the vertical fluxes of heat and momentum in the tropical Pacific equatorial undercurrent (EUC) system is one of the central problems linking the small-scale physics of flow instabilities and turbulent mixing to larger scale climatic variability such as ENSO. Significant progress has been made in the last two decades, spurred primarily by simultaneous observations of mean and turbulent vertical profiles combined with classical linear stability analyses. Nevertheless, significant uncertainty remains and, in particular, the mechanisms by which a unique mix of high-frequency internal waves and coherent turbulence patches is initiated and sustained at depths where the background shear is linearly stable are only poorly understood. In this project, a high-resolution numerical investigation will be conducted to quantify the pathways through which energy sources - surface wind, buoyancy flux and mean kinetic energy of the jet - feed into turbulent dissipation. The improved modeling capability in this project, based primarily on high-resolution LES will complement on-going observational programs. These three-dimensional, non-hydrostatic simulations performed on large-scale NSF computational facilities will directly resolve the flow instabilities leading to turbulence and vertical fluxes. The analysis of the space-time dataset will focus on elucidating the finite amplitude, nonlinear mechanisms responsible for sustaining turbulence in regions where background conditions are linearly stable. The modeling will incorporate the new observations in the form of background profiles of shear and stratification with corresponding wind stress and heat flux. The principal objective of the effort will be to understand the physical mechanisms of turbulence generation and transport operative in the EUC under a variety of conditions and to quantify the associated energy transport and vertical fluxes.Broader Impacts: Scientifically, the proposed effort will contribute to the development of physically based parameterizations and predictive capabilities of broad societal interest. The project will directly support the training of one post-doctoral scholar of Vietnamese origin, an under-represented community in science. It will contribute to the development of computational and information technology infrastructure through collaboration with an existing NSF funded project on database design for computational fluid dynamics simulations. The project will also directly support graduate education at UCSD by incorporating analytical and numerical techniques and results into existing courses in environmental and computational fluid dynamics cross-listed between Mechanical and Aerospace Engineering and the Scripps Institution of Oceanography at UCSD. The cross-disciplinary nature of the PI team will ensure broad dissemination of the results among the geosciences and engineering communities.