Along-isopycnal Salinity Variability: Deducing Horizontal Stirring in the Global Ocean from Argo

概述：沿密度表面的扩散是决定示踪剂在海洋中分布的一个重要因素。扩散是由涡场决定的，各种大小的涡流在海洋中水平搅动着示踪物。水平搅拌的一个特征是温度和盐度沿密度表面的波动，这是一种经常观察到但分析不足的示踪剂。最近的细尺度观测表明，这些沿密度面的波动被组织成在时间上持续数年的升高的波动区域；这表明涡旋搅拌的基本过程在地理上是不同的，并且在时间上是稳定的，通过在全球尺度上调查温度和盐度波动可以获得许多成果。智力优势：这个项目将使用Argo浮子数据来研究沿密度表面的盐度变化，即所谓的等密度面。将对近全球海洋从表层到1000-2000米深的混合长度和水平扩散系数进行估计，并对影响水平扩散的过程进行评估。沿等温盐度波动的方差将与平均盐度的水平和垂直梯度进行比较。特别是与水平梯度的相关性表明，可用于搅拌的梯度是最重要的，混合长度框架是估计水平扩散系数的有效方法。在近全球海洋，水平扩散率将使用卫星测高得出的混合长度和速度起伏以及混合层、西部边界流区和近1000米深的额外估计(后者利用从Argo漂移得到的速度起伏)来估计。沿等温盐度波动、混合长度和水平扩散系数的地理变化将显示水平搅拌如何随位置、深度、平均速度和示踪场以及海洋的其他相关特征而变化。更广泛的影响：这项研究的结果将直接提高我们对示踪剂分布、海洋环流和地球气候的理解。混合长度和水平扩散系数的深度结构将提供涡旋搅动如何随深度变化的观测估计，可以与模拟研究进行比较，并用于改进其在数值模式中的参数化。对哪些过程主要控制示踪剂波动的演变的评估将使目前或未来其他水平扩散率估计的方法得以评估，特别是海面以下的估计。这项研究中使用的方法可以在今后推广，以包括来自其他示踪剂的额外信息。该奖项还将支持一位早期职业海洋学家进行她的第一个独立研究项目。

Overview: Diffusion along density surfaces is a significant factor in determining the distribution of tracers in the ocean. Diffusion is determined by the eddy field with eddies of all sizes horizontally stirring tracers in the ocean. One signature of horizontal stirring is fluctuations of temperature and salinity along density surfaces, a frequently observed but under-analyzed tracer. Recent fine-scale observations show that these along-density surfaces fluctuations are organized into regions of elevated fluctuations that are temporally persistent over several years; this suggests that the underlying processes of eddy stirring are geographically varied and steady in time with much to be gained by investigating temperature and salinity fluctuations on a global scale. Intellectual Merits: This project will use Argo float data to investigate salinity variability along density surfaces known as isopycnals. Mixing length and horizontal diffusivity estimates, as well as an assessment of the processes that influence horizontal diffusion, will be made from the surface to 1000-2000 m depth in the near-global ocean. The variance of along-isopycnal salinity fluctuations will be compared to horizontal and vertical gradients of mean salinity. A correlation with horizontal gradients in particular indicates that the gradient available to stir is of primary importance and a mixing length framework is a valid approach for estimating horizontal diffusivity. In the near global ocean, horizontal diffusivity will be estimated using mixing length and velocity fluctuations derived from satellite altimetry, as well as additional estimates in the mixed layer, western boundary current regions, and near 1000 m depth (the later utilizing velocity fluctuations derived from Argo float drifts). Geographic variations in along-isopycnal salinity fluctuations, mixing length, and horizontal diffusivity will show how horizontal stirring varies with location, depth, mean velocity and tracer fields, and other relevant features of the ocean.Broader Impacts: Results from this study will directly improve our understanding of tracer distributions, ocean circulation, and earth's climate. The depth structure of mixing length and horizontal diffusivity will provide an observational estimate of how eddy stirring changes with depth that can be compared against modeling studies, and used to improve their parameterization in numerical models. An assessment of which processes predominantly control the evolution of tracer fluctuations will allow the methods of other current or future horizontal diffusivity estimates to be evaluated, especially estimates below the ocean surface. The methods utilized in this study can be generalized in the future to include additional information from other tracers. This award will also support an early career oceanographer in her first independent research project.