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

概述：沿密度面扩散是决定示踪剂在海洋中分布的一个重要因素。扩散是由海洋中各种大小的涡旋水平搅拌示踪剂的涡流场决定的。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物。最近的精细尺度观测表明，这些沿密度表面的波动被组织成高波动区域，这些高波动在时间上持续数年；这表明涡旋搅拌的潜在过程在地理上是变化的，在时间上是稳定的，通过研究全球尺度上的温度和盐度波动可以获得很多信息。智力优势：该项目将使用Argo浮子数据来研究沿密度面（即等平面）的盐度变化。将对近全球海洋从表面到1000-2000米深度的混合长度和水平扩散率进行估计，并对影响水平扩散的过程进行评估。将沿等气旋盐度波动的方差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率的有效方法。在近全球海洋，将利用卫星测高数据得出的混合长度和速度波动来估计水平扩散率，并在混合层、西部边界流区域和1000 m深度附近进行额外估计（后者利用Argo浮子漂移得出的速度波动）。沿等压轴盐度波动、混合长度和水平扩散率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率的深度结构将提供旋涡搅拌随深度变化的观测估计，可以与模型研究进行比较，并用于改进数值模型中的参数化。评估哪些过程主要控制示踪剂波动的演变，将有助于评估当前或未来其他水平扩散率估算方法，特别是海洋表面以下的估算方法。本研究中使用的方法可以在未来推广，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生涯的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.