Parametrizing ocean eddy transfer over continental slopes

陆坡支撑着世界海洋环流中一些最有影响力的洋流，例如亚热带地区发现的像墨西哥湾流这样的向极地移动的强大西部边界流。然而，横跨大陆斜坡的环流可以说具有同等的重要性，因为它们将浅海水域与深海的水团分开。横跨大陆斜坡的水团交换促进营养物质的上升，以支持沿海海洋生态系统，将热量输送到格陵兰和南极洲周围的海洋末端冰川，并控制地中海水和南极底层水等稠密水团的外流。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横向转移方面具有重要意义。预测性海洋和气候模式目前无法解决这些漩涡，而且至少在未来几十年内也不太可能在全球范围内定期解决中尺度问题。然而，尽管最近在平坦海床上的涡旋的参数化策略方面取得了重大进展，但还没有协调一致的努力来开发针对大陆斜坡的类似策略。该项目旨在弥合目前在理解陡坡上的中尺度湍流方面的差距，从而开发大陆坡上涡旋混合和输送的参数化。该项目将为研究生研究人员提供为期三年的数值和分析建模培训以及观测数据集的实用知识。它还支持一名职业生涯早期的教职员工。该项目的一个主要目标是就如何处理大陆斜坡上的中尺度涡旋输送问题提出一套建议，这些建议将在海洋学和气候界广泛传播。采用这些做法可以大大改善大规模海洋和气候模式中陆架和坡度过程的表现。该项目的模型输出将提供给更广泛的海洋学界，以进行测试和验证。首席调查员还将通过研究所支持的现有框架参加外联活动。该项目的一个中心目标是探索各种强迫条件、海洋分层和斜坡几何形状的大陆斜坡上平衡湍流的基本性质。这项工作将描述斜率S对涡旋生命周期和产生机制的影响，质量和示踪物质的横向和沿斜率的涡动输送，地面输入动量和能量的耗散途径，斜率流中涡动动能的来源和产生，以及对逆能量级联和急流形成的约束。在强斜压沿岸流中，有丰富的势能可用于中尺度涡旋的产生，但陡峭的地形往往会抑制能量转换为中尺度涡旋运动，从而抵消了能量的可获得性。这些补偿效应在设定涡旋转移和混合速率方面的相对作用仍不清楚。首席调查员和一名研究生研究员将开发一个涡旋解析过程模型，并创建一套大陆架和斜坡测试案例，其结果将向更广泛的海洋学界提供。这套模拟将被用来描述斜坡湍流的关键特性，例如能量和动量的收支，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希望的理论方法，以构建陡峭地形上的涡旋传输的参数化。将根据一套涡旋解析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来测试和验证参数化。这项工作的结果将被用来制定一套建议和最佳做法，用于将大陆斜坡上的中尺度涡旋参数化，并将其广泛传播给海洋和气候建模人员。

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.