Along-isopycnal transport in the Southern Ocean: Assessing DIMES results with an assimilating model

智力成果：南大洋纵贯和等密度混合实验旨在评价沿南大洋急剧倾斜的密度面沿着的等密度（主要是水平）混合的作用，同时确定有可能改变中层水特性的纵贯（主要是垂直）混合过程的程度。这两个过程一起是全球纬向翻转环流的关键贡献者。DIMES进行了广泛的取样方案，包括声学跟踪地下浮子、中等深度示踪剂释放、系泊阵列和水属性调查。现在已经收集了大量的DIMES数据，本项目的目标是最佳地利用DIMES观测，将其用作海洋环流模型的约束条件，即南大洋状态估计，该模型使用四维变分数据同化技术运行。SOSE将提供DIMES研究领域背景条件的最佳估计，这对DIMES浮动和示踪剂分析至关重要。SOSE场将与DIMES和其他独立观测进行密切比较，以评估SOSE中的不确定性，以及DIMES观测及其拉格朗日混合的衍生估计中的不确定性。SOSE场将揭示DIMES域和整个南大洋的等密混合和海洋热输送的细节。在DIMES领域关于等密度线混合的经验教训将推广到整个南大洋，以评估等密度线混合的空间变化及其对当地水深、风和浮力强迫的敏感性。SOSE领域也将进行分析，以评估强度的纬向翻转环流，并评估极地热量输送整个ACC和对气候敏感的冰架周围Antarctics.Broader影响：使用SOSE为这个项目进行的研究将有助于更广泛的多机构，多PI的努力来解释收集的数据作为DIMES的一部分，与发展的最终目标是更好地了解沿等密度线和diapycnal混合过程中的海洋。SOSE的输出将公开提供，供DIMES附属研究小组和其他感兴趣的研究人员进行分析。状态估计设置（前向和伴随模型）将由DIMES研究小组处理，以支持其科学目标。DIMES的结果将最终导致对这些混合过程的更好的物理理解，并建议改进用于未来气候预测的数值模式的混合参数化。此外，该项目还将帮助培训一名目前拥有美国航天局地球系统科学研究生奖学金的研究生，并将为一名博士后研究员提供支助，该研究员将发展同化和模式分析方面的技能，该项目是对美国气候变率和可预测性方案的贡献。

Intellectual Merit:The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) is designed to evaluate the role of isopycnal (mostly horizontal) mixing along the steeply tilted density surfaces of the Southern Ocean, and at the same time to determine the magnitude of diapycnal (mostly vertical) mixing processes that have the potential to transform water properties at mid-depth. Together these two processes are key contributors to the global meridional overturning circulation. DIMES carried out an extensive sampling program including acoustically-tracked sub-surface floats, a mid-depth tracer release, a mooring array and water property surveys. Now that the bulk of DIMES data collection has taken place, the objective of this project is to make optimal use of the DIMES observations by employing them as constraints for an ocean general circulation model, the Southern Ocean State Estimate (SOSE), which is run using a 4-dimendional variational data assimilation technique. SOSE will provide best estimates of the background conditions in the DIMES research domain, which is vital for the DIMES float and tracer analysis. SOSE fields will be closely compared with DIMES and other independent observations to provide an assessment of uncertainties in SOSE, as well as uncertainties in the DIMES observations and in its derived estimates of Lagrangian mixing. SOSE fields will reveal the details of isopycnal mixing and oceanic heat transport in the DIMES domain and throughout the Southern Ocean. Lessons learned in the DIMES domain about isopycnal mixing will be extended to the entire Southern Ocean to evaluate spatial variations in isopycnal mixing and its sensitivity to local bathymetry, wind, and buoyancy forcing. SOSE fields will also be analyzed to evaluate the strength of meridional overturning circulation, and to assess poleward heat transport across the ACC and towards the climatically sensitive ice shelves surrounding Antarctica.Broader Impacts:Research conducted for this project using SOSE will contribute to the broader multi-institution, multi-PI efforts to interpret data collected as part of DIMES, with the ultimate goal of developing a better understanding of along-isopycnal and diapycnal mixing processes in the ocean. Output from SOSE will to be made publicly available to be used for analysis by DIMES-affiliated research groups and by other interested researchers. The state estimate setup (forward and adjoint model) will be at the DIMES research groups' disposal for additional runs in support of their science goals. Results from DIMES will ultimately lead to better physical understanding of these mixing processes and suggest improvements in the mixing parameterizations of numerical models used for future climate projections. In addition, the project will contribute to the training of one graduate student who currently holds a NASA Earth System Science graduate fellowship and will provide support for a post-doctoral researcher, who will develop his skills in assimilation and model analysis.This project is a contribution to the U.S. CLIVAR (Climate Variability and Predictability) Program.