Extending Abyssal Mixing Observations and Parameterizations

智力优势：观测研究表明，在海洋内部只存在微弱的贯向混合，在地形粗糙的区域，靠近海底的混合要多几个数量级。相比之下，数值环流和气候模式一般采用空间统一的参数化深海底辟混合。然而，最近的几项数值研究表明，大尺度深海环流对深海贯入混合的空间分布很敏感，这使模型制作者认识到，为了改进海洋环流的模拟，需要模拟观测到的空间变化的混合参数化。妨碍改进深海混合参数化的制定和验证的一个主要问题是观测不足。微结构观测，最直接和准确的工具，推断diapycnal混合，只完成了在全球海洋的几个选定的区域，不幸的是，不会成为一个常规的测量在不久的将来，由于其成本和必要性非常高的质量控制水平。因此，许多工作都集中在如何间接地从标准水文数据推断diapycnal混合，可能会产生一个更密集的采样全球地图diapycnal混合。一个现在常见的方法是应用程序的精细尺度参数化，湍流耗散的剪切和/或应变方差的规模为10米，非线性内波波相互作用理论的基础上。然而，越来越明显的是，细尺度参数化仅在非常有限的条件范围内是可靠的预测因素。已知该方法在特殊环境（例如，海岸斜坡，峡谷），是一个差的预报员的diapycnal混合在弱分层的水。由于全球深海（深度1 000米）和南大洋都属于这一类，因此分层限制很严重。深海和南大洋是经向翻转环流的重要分支，因此气候模拟研究的可信度取决于这些海洋体积中的底辟混合的准确表示。将使用索普尺度分析法重新分析世界海洋环流实验的水文数据。索普尺度分析已被证明是一个更强大的预测耗散和diapycnal混合比细尺度参数化，特别是在弱分层和地区的内部波场的特性偏离规范Garrett-Munk模型，但尚未被广泛应用于WOCE水文数据集。这项工作的预期成果是，对深海混合的空间分布有更好的观测认识。我们还提出了一个全面的比较和验证现有的深海混合参数化打算用于大气环流和气候模式。更广泛的影响：本提案中要求的资金旨在支持博士后研究人员。该项目的成果将在参考文献中传播，在网上提供，并在适当的科学会议上介绍。混合的空间变异性显著影响深海环流和层化、南极绕极流的强度和深度以及南极翻转环流的各个方面。反过来，这些关系到海洋储存和输送热量和温室气体的能力，从而关系到气候系统对人为和自然强迫的反应。预计该项目将使人们对混合的空间分布有更好的观测了解，并有助于改进用于海洋环流模型和气候模型的纵贯混合参数化。

Intellectual Merit: Observational studies suggest the existence of only weak diapycnal mixing in the ocean interior, with orders of magnitude more mixing near the bottom in regions of rough topography. In contrast, numerical circulation and climate models generally employ spatially uniform parameterizations of abyssal diapycnal mixing. However, several recent numerical studies demonstrate the sensitivity of the large scale abyssal ocean circulation to the spatial distribution of abyssal diapycnal mixing, leading modelers to recognize that mixing parameterizations mimicking the observed spatial variability are required to improve simulations of the ocean circulation.As is typical in oceanography, a major problem hampering both the development and validation of improved abyssal mixing parameterizations is the scarcity of observations. Microstructure observations, the most direct and accurate tool with which to infer diapycnal mixing, have only been accomplished in a few select regions of the global ocean and will unfortunately not become a routine measurement in the near future due to their cost and the necessity for very high levels of quality control. Consequently, much work has focused on ways to infer diapycnal mixing indirectly from standard hydrographic data, potentially yielding a much more densely sampled global map of diapycnal mixing. A now common approach is the application of fine-scale parameterizations, relating turbulent dissipation to shear and/or strain variance on scales of order 10 meters, based on nonlinear internal wave-wave interaction theory. However, it is becoming increasingly clear that fine-scale parameterizations are reliable predictors only for a very limited range of conditions. The method is known to break down in special environments (e.g., the coastal slope, canyons) and to be a poor predictor of diapycnal mixing in weakly stratified water. The stratification limitation is severe since both the global abyssal ocean (depth 1000 m) and the Southern Ocean fall in that category. The abyssal and Southern Ocean are important branches of the Meridional Overturning Circulation and thus the credibility of climate modeling studies depends on accurate representation of diapycnal mixing in these ocean volumes. The World Ocean Circulation Experiment (WOCE) hydrographic data will be re-analyze using Thorpe scale analysis. Thorpe scale analysis has been shown to be a more robust predictor of dissipation and diapycnal mixing than fine-scale parameterizations, in particular in weak stratification and regions where the characteristics of the internal wave field deviate from the canonical Garrett-Munk model, yet has not been applied extensively to the WOCE hydrographic data set. The expected results from this work are an improved observational knowledge of the spatial distribution of mixing in the abyssal ocean. We also propose a comprehensive comparison and validation of existing abyssal mixing parameterizations intended for use in general circulation and climate models. Broader Impacts: The funds requested in this proposal are intended for the support of a postdoctoral investigator. The results from this project will be disseminated in the refereed literature, made available online and presented at appropriate scientific meetings. The spatial variability of mixing significantly affects the abyssal circulation and stratification, the strength and depth of the Antarctic Circumpolar Current as well as various aspects of the meridional overturning circulation (MOC). In turn, these relate to the ability of the ocean to store and transport heat and greenhouse gasses, and thus the response of the climate system to anthropogenic and natural forcing. This project is expected to result in a better observational knowledge of the spatial distribution of mixing than achieved to date, and to contribute to the improvement of diapycnal mixing parameterizations intended for ocean general circulation models and climate models.