DBE Synthesis Supplement: Deep Circulation in the Tropical and Subtropical South Atlantic

0220407 Speer在世界海洋环流实验下的深盆地实验过程中，建立了一个新的热带和亚热带南大西洋水文和示踪气候学，并对水文剖面进行了重新分析。在大西洋中脊（巴西盆地）以西的水文剖面中观察到的纬向密度梯度表明，在大的空间尺度上，持续的纬向流具有明显的规律性，与新气候学中几种示踪剂的等密度分布一致。这种交替的纬向流模式在最先进的数值模式的输出中也很明显。虽然观测（以及模式）表明，平均深环流的概念是明智的，他们也表明，它是不可能确定的时间平均地转流天气观测，通过简单地确定一个参考速度（正压调整）。在巴西盆地的天气和时间平均的地转纬向速度场之间的差异是斜压的，并在时间和空间上变化。在南大西洋的水文观测和数值纬向流之间的良好协议表明，它可以使用数值结果分离成长期平均和低频时变分量的意见。目前的分析将扩大并应用于南大西洋更大的区域，首要目标是定量描述WOCE期间热带和亚热带南大西洋的深层环流。第一步将包括分析的时空结构的时变模型流，以指导分离的时变的平均地转流从水文剖面确定。当然，该模型似乎模拟了巴西盆地的平均纬向流，这一事实并不意味着随时间变化的流量得到了很好的代表。虽然不可能从现有水文剖面直接估计时变流分量，但对个别剖面的分析以及两个水文剖面之间的差异将使PI能够比较时变流场的重要方面，如空间尺度和斜压结构与模型输出。此外，最近的分析结果的时变流量来自？燕麦数据（Hogg等人，2002年）将用于比较。除了揭示深环流的新方面（对气候、示踪剂扩散、水文学等的影响）外，拟议项目的结果将大大改善天气水文剖面的分析，对反演模型具有重要意义，因此，对根据WOCE数据集确定平均环流具有重要意义。数值模型输出和海洋数据的直接比较是拟议项目的一个内在组成部分，将揭示当前数值模型的优点，更重要的是，弱点。这些见解将有助于改进模型。

0220407 SpeerIn the course of the Deep Basin Experiment under the World Ocean Circulation Experiment (WOCE) a new hydrographic and tracer climatology of the tropical and subtropical South Atlantic was constructed and a re-analysis of hydrographic sections was carried out. The meridional density gradients observed in hydrographic sections west of the Mid-Atlantic Ridge (in the Brazil Basin) indicate a strikingly regular pattern of persistent zonal flows coherent over large spatial scales, consistent with the isopycnal distributions of several tracers in the new climatology. This pattern of alternating zonal flows is also apparent in the output from a state-of-the-art numerical model. While the observations (as well as the model) indicate that the notion of a mean deep circulation is sensible they also show that it is not possible to determine the time-averaged geostrophic flows from synoptic observations by simply determining a reference velocity (barotropic adjustment). The difference between the synoptic and the time-averaged geostrophic zonal velocity fields in the Brazil Basin is baroclinic and varies both in time and space. The excellent agreement between the hydrographically observed and the numerical zonal flows in the South Atlantic suggests that it possible to use the numerical results to separate the observations into long-term mean and low-frequency time-varying components. The current analysis will be extended and applied it to a larger region of the South Atlantic with the overriding goal to quantitatively describe the deep circulation in the tropical and subtropical South Atlantic during the WOCE period. The first step will consist of analyzing the spatio-temporal structure of the time-varying model flow to guide the separation of the time-varying from the mean geostrophic flows determined from the hydrographic sections. The fact that the model appears to simulate the mean zonal flows in the Brazil Basin realistically does not imply that the time-varying flows are as well represented, of course. While it is not possible to directly estimate the time-varying flow component from available hydrographic sections analysis of individual profiles as well as differences between two hydrographic sections will allow the PI's to compare important aspects of the time-variable flow field, such as spatial scales and baroclinic structure to the model output. Furthermore, the results of a recent analysis of the time-varying flows derived from ?oat data (Hogg et al. , 2002) will be used for comparison. In addition to revealing new aspects of the deep circulation (with implications for climate, tracer dispersal, biogeography, etc.), the results of the proposed project will significantly improve the analysis of synoptic hydrographic sections with important implications for inverse models and, therefore, for determining the mean circulation from the WOCE data sets. Direct comparison of numerical-model output and oceanic data is an intrinsic part of the proposed project and will reveal strengths and, more importantly, weaknesses of current numerical models. These insights will be useful for improving the models.