Air-Sea Exchange in the Southern Ocean

该奖项是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。在南大洋，海-气通量在改变海洋表面的水方面发挥着关键作用。它们确定了当水被表面埃克曼流带到北方时，水的性质是如何变化的，这是子午线翻转环流的一部分。它们还确定了从南极绕极洋流北侧向下向中深处的中间和模式水域的性质，携带着它们与大气接触的指纹。数值天气预报(NWP)模式或卫星和现场数据的详细分析提供了一些格网海气通量产品。这些产品的时间平均差异很大，通常是每平方米50瓦或更多。此外，现有的通量产品不足以完全解释观测到的混合层热含量的季节变化和年际变化。此外，虽然海-气通量被认为在与锋面或涡旋等中尺度海洋特征相关的小空间尺度上变化，但小尺度变化通常不能在海-气通量产品中得到解决。这项工作所依据的假设是，改进海-气通量估算是改善对南大洋混合层过程的理解的重要一步。将利用估计的热量和淡水通量来评估三个关键概念：(A)南大洋的表层水团变化可以主要通过海-气热量和淡水通量来解释，而不需要启动任何次表层过程。(B)应在区域和全系统范围内关闭上层海洋热平衡。上层海洋温度的季节和年际变化应该主要是由海-气热通量来解释的，水平平流过程是差异的主要原因。(C)表面通量的小空间尺度、快速变化很大程度上造成了海气热通量和淡水通量的现有不确定性，解决这些小尺度通量将减少上层海洋热量收支的不确定性。本质上，这三个假设转化为一个单一的概念，即改进我们对热通量的估计应该提高我们对发生在南大洋的气候尺度过程的物理理解。将通过考虑海-气通量表现的两个指标来评估在南大洋规模上重要的过程：时间演变的混合层热量收支的闭合以及由海-气通量驱动的向北的Ekman平流和水质量转换之间的时间平均平衡。将评估一套现有的通量产品，并将通过测试可能的参数来开发新的混合通量估计，以找到一组最佳的卫星和数值天气预报产品，以提供给用于计算海-气通量的整体算法。在区域尺度上，将利用船上气象资料评估海气通量的小尺度结构。布拉德影响：该项目将提供部分支持，以培养一名海气交流重要领域的博士后研究员。作为这项研究的一部分，对南大洋海-气热量和淡水通量的估计将通过一个网站发布。研究结果将有助于为未来在海气通量及其在气候中的作用方面的进展奠定基础。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).In the Southern Ocean, air-sea fluxes play a critical role in transforming water at the ocean surface. They determine how water properties change when water is carried northward by surface Ekman currents as part of the meridional overturning circulation. They also determine the properties of Intermediate and Mode Waters that descend to mid-depth from the northern flank of the Antarctic Circumpolar Current, carrying with them fingerprints of their contact with the atmosphere. A number of gridded air-sea flux products are available from numerical weather prediction (NWP) models or detailed analyses of satellite and in situ data. These products differ substantially, often by 50 Watts per square meter or more in the time-averaged mean. In addition, the existing flux products are not accurate enough to explain fully the observed seasonal to interannual variations in the mixed-layer heat content. Moreover, while air-sea fluxes are thought to vary over small spatial scales associated with mesoscale ocean features such as fronts or eddies, small-scale variations are typically not resolved in air-sea flux products.Intellectual Merit: This research project will investigate the mixed-layer heat budget and water mass transformation in the Southern Ocean. The work is predicated on the hypothesis that improving air-sea flux estimates is an essential step towards an improved understanding of Southern Ocean mixed-layer processes. Heat and freshwater flux estimates will be used to evaluate three key ideas: (a) Surface water mass transformation in the Southern Ocean can be explained primarily through air-sea heat and freshwater fluxes, without requiring that any subsurface processes be invoked. (b) The upper ocean heat balance should close, both regionally and on a system-wide scale. Seasonal to interannual variations in upper ocean temperature should be explainable largely by air-sea heat fluxes, with horizontal advective processes making up most of the difference. (c) Small-spatial scale, rapid variations in surface fluxes are significant, contributing much of the existing uncertainty in air-sea heat and freshwater fluxes, and resolving these small-scale fluxes will reduce the uncertainties in upper ocean heat budgets. In essence, these three hypotheses translate into a single concept, that improving our estimates of heat fluxes should improve our physical understanding of the climate-scale processes that occur in the Southern Ocean. Processes that matter on the scale of the Southern Ocean will be evaluated by considering two metrics of air-sea flux performance: the closure of a time-evolving mixed-layer heat budget and time-averaged balance between northward Ekman advection and water mass conversion driven by air-sea fluxes. A suite of existing flux products will be evaluated, and a new, hybrid flux estimate will be developed by testing possible parameters to find an optimal set of satellite and numerical weather prediction products to feed into the bulk algorithms used to compute air-sea fluxes. On a regional scale, shipboard meteorological data will be used to assess the small-scale structure of air-sea fluxes.Braoder Impacts: The project will provide partial support in order to train one postdoctoral researcher in the important area of air-sea exchange. Estimates of Southern Ocean air-sea heat and freshwater fluxes derived as part of this research will be released via a website. Research findings will help to lay the groundwork for future advances in air-sea fluxes and their role in climate.