Parametrizing ocean eddy transfer over continental slopes

大陆坡支撑着世界海洋环流中一些最具影响力的洋流，例如在亚热带地区发现的强大的向极地的西边界洋流。但是，可以说，跨越大陆坡的环流具有类似的重要性，因为它们将沿海浅水沃茨与深海水团分隔开来。跨越大陆坡的水团交换促进了营养物质的上涌，以支持沿海海洋生态系统，将热量输送到格陵兰岛和南极洲周围的海洋终止冰川，并控制地中海水和南极底层水等密集水团的外流。 最近的研究指出，中尺度涡旋在调节沿岸流的结构和输送以及水团和性质的跨坡转移方面具有重要意义。预测性海洋和气候模型目前无法解决这些涡旋，并且至少在几十年内不太可能常规解决全球中尺度问题。然而，尽管最近在平坦洋底上空涡旋的参数化战略方面取得了重大进展，但没有协调一致的努力为大陆坡制定类似的战略。 该项目旨在填补目前在理解陡坡上中尺度湍流方面的空白，从而制定大陆坡上涡流混合和输送的参数化。该项目将为研究生研究员提供三年的数值和分析建模培训以及观测数据集的工作知识。它还支持早期职业教师。该项目的一个主要目标是提出一套建议，用于处理大陆坡上空的中尺度涡流输送，并将在海洋学和气候学界广为传播。采用这些做法可以大大改善大尺度海洋和气候模型中大陆架和陆坡过程的表现。该项目的模型输出将提供给更广泛的海洋学界，以供测试和验证。主要研究员还将通过其所在机构支持的现有框架参与外展活动。该项目的中心目标是探索在各种强迫条件、海洋分层和斜坡几何形状下大陆坡平衡湍流的基本特性。这项工作将描绘斜坡？的涡流的生命周期和生成机制的影响，跨和沿坡涡流传输的质量和示踪剂，到表面输入的动量和能量的耗散的路线，在斜坡流的涡流动能的来源和生成，以及对逆能量级联和射流形成的约束。在强斜压沿岸流中，有丰富的势能可用于产生中尺度涡旋，但能量的可用性可能被陡峭的地形所抵消，这往往会抑制能量转化为中尺度涡旋运动。这些补偿效应在设定涡流传输和混合速率方面的相对作用仍然知之甚少。首席调查员和一名研究生将开发一个涡流分解过程模型，并创建一套大陆架和斜坡测试案例，其结果将提供给更广泛的海洋学界。这套模拟将用于表征斜坡湍流的关键特性，如能量和动量的预算，以及涡流的生命周期。在这些发现的指导下，研究小组将探索几种有前途的理论方法，以建立陡峭地形上涡流传输的参数化。将根据一套涡解模拟以及现有的卫星海面高度数据和沿海浮标释放数据数据库对参数化进行测试和验证。这项工作的结果将用于制定一套建议和最佳做法，以确定大陆坡上空中尺度涡旋的参数，并将广泛分发给海洋和气候建模者。

Continental slopes support some of the most influential currents in the world ocean circulation, such as the strong poleward western boundary currents like the Gulf Stream found in the subtropics. However, the circulation across continental slopes is arguably of comparable importance, as they separate shallow coastal waters from the water masses of the deep ocean. Water mass exchanges across continental slopes facilitate upwelling of nutrients to support coastal marine ecosystems, transport heat towards marine-terminating glaciers around Greenland and Antarctica, and control the outflow of dense water masses such as Mediterranean Water and Antarctic Bottom Water. Recent studies point to the importance of mesoscale eddies in modulating both the structure and transport of coastal currents and the cross-slope transfer of water masses and properties. Predictive ocean and climate models are currently unable to resolve these eddies, and are unlikely to routinely resolve the mesoscale globally for at least a couple of decades. Yet despite major recent advances in parametrization strategies for eddies over a flat ocean bed, there have been no concerted attempts to develop analogous strategies for continental slopes. This project aims to close the current gap in understanding mesoscale turbulence over steep slopes, and thereby to develop a parametrization of eddy mixing and transport over continental slopes. This project will provide a graduate student researcher with three years of training in numerical and analytical modeling as well as working knowledge of observational datasets. It also supports an early-career faculty member. A key objective of this project is to produce a set of recommendations for the treatment of mesoscale eddy transport over continental slopes, which will be disseminated widely among the oceanographic and climate communities. Adoption of these practices could substantially improve the representation of shelf and slope processes in large-scale ocean and climate models. The project's model output will be made available to the wider oceanographic community for the purpose of testing and validation. The principal investigator will also participate in outreach activities via existing frameworks supported by his institution.A central goal of this project is to explore the fundamental properties of equilibrated turbulence over continental slopes across a range of forcing conditions, ocean stratifications and slope geometries. The work will characterize the slope?s impact on the eddy life cycle and generation mechanisms, cross- and along-slope eddy transfer of mass and tracers, the routes to dissipation of surface-input momentum and energy, sources and generation of eddy kinetic energy in slope currents, and constraints on the inverse energy cascade and jet formation. In strongly baroclinic coastal currents there is an abundance of potential energy available for the generation of mesoscale eddies, but the availability of energy may be offset by the steep topography, which tends to suppress energy conversion to mesoscale eddy motions. The relative roles of these compensating effects in setting rates of eddy transfer and mixing remains poorly understood. The principal investigator and a graduate student researcher will develop an eddy-resolving process model and create a suite of continental shelf and slope test cases, the output of which will be made available to the wider oceanographic community. This suite of simulations will be used to characterize key properties of slope turbulence, such as the budgets of energy and momentum, and the eddy life cycle. Guided by these findings, the research team will explore several promising theoretical approaches toward the construction of a parametrization of eddy transfer over steep topography. The parametrization will be tested and validated against the suite of eddy-resolving simulations, and against existing databases of satellite-derived sea-surface height data and coastal float release data. The findings of this work will be used to create a set of recommendations and best practices for parametrizing mesoscale eddies over continental slopes, which will be disseminated widely to ocean and climate modelers.