Circulation and Vorticity Dynamics of Laboratory Sill and Basin Flows

最近的海洋观测(例如，法罗海峡和丹麦海峡)显示了海峡水流的时间依赖和稳定成分，以及下游混合的某些方面。然而，人们对供给海峡的水流的结构以及海峡水流如何与上游盆地环流耦合的了解要少得多。其次，最近的理论和数值工作提出了一种新的耦合机制，但没有观测数据，也没有多少实验室实验数据来检验和推广这些新想法。提出的理论和实验室实验之间的比较可以用来建议未来的海洋观测和可能的溢出监测策略。其目的是提供尽可能多的信息来指导未来的海洋巡航、一般环流理论和数值气候模拟项目将开发和进行实验室实验，以研究有限旋转盆地中的环流与水力控制的基准流的耦合。这种情况通常适用于一层层的深水，从一个被这种水填满的深海盆地，通过冷水层或最深的鞍点通道进入另一个盆地。在下游盆地，水的密度通常较低。其目的是获得定量的测量结果，用以研究盆地环流，包括任何支流、盆地-海峡耦合系统的潜在涡度动力学以及海峡中的水力流动。最近的一项数值研究表明，海峡对盆地施加了一种新的、尚未解释的潜在涡度控制。对这一机制的探索将是本研究的出发点。拟议的实验将在WHOI GFD实验室一米和两米的转台上进行，转台上有一个上游盆地和一个通往小集水池的通道。这项工作将首先探索空气中的水流动，以便能够研究上游盆地和海峡中粘性影响相对较小的流动。它还计划将咸水抽到较深的淡水(减重配置)下，在那里可以探索上游盆地中增加的旋转效应和增加的摩擦效应的作用。有两个活性层的实验可能会在工作的后期阶段进行检查。将调查各种上游几何条件(例如，平坦和碗形盆地)以及不同质量源特征(例如，边界流入和内部下流)的作用。在所有情况下，都将在盆地和通道内测量各种相关参数的层深和速度分布(使用粒子成像技术)。实验工作将与世界卫生组织已经在进行的类似理论和数值工作平行进行，并与之进行比较。更广泛的影响：深通道为监测倾覆的环流提供了理想的点。然而，只有在了解海峡水流和盆地水流之间的动态联系的情况下，这才能正确地完成。这项工作将开始回答其中的一些问题，并应引起广泛的兴趣，而不是这里探索的特定动态。PIs在麻省理工学院/WHOI联合计划中都很活跃，这项研究的结果将很快进入课堂。这笔助学金还将资助一名研究生，从而进一步促进更广泛的教育目标。最后，这笔赠款总体上将支持世界卫生组织地球物理流体动力学实验室，这是世界上为数不多的此类设施之一。世界卫生组织GFD实验室在帮助来自世界卫生组织和世界各地的科学家和学生在广泛的流体动力学问题上进行实验工作方面有着悠久的历史。

Recent oceanic observations (e.g., Faroe passage and Denmark Strait) show time-dependent and steady components of the strait flows, and aspects of the downstream mixing. However, much less is know about the structure of the currents which feed the straits and how the strait flow is coupled to the upstream basin circulation. Second, recent theoretical and numerical work suggests a novel coupling mechanism, but there are no observational data and few laboratory experimental data with which to test and generalize these new ideas. The proposed comparisons between theory and laboratory experiments can be used to suggest future oceanic observations and possible overflow monitoring strategies. The intent is to provide as much information as possible to guide future ocean cruises, general circulation theory, and numerical climate modeling projectsLaboratory experiments will be developed and conducted to investigate the coupling of circulation in a finite, rotating basin with the hydraulically controlled flow over a sill. This situation usually applies to layers of deep water passing from one deep ocean basin, which is filled by this water, to another basin through a col, or the deepest saddle point passage. In the downstream basin the water is typically less dense. The goal is to obtain quantitative measurements with which to examine the basin circulation, including any feeder currents, the potential vorticity dynamics of the coupled basin-strait system, and the hydraulic flow in the strait. A recent numerical study showed a novel, and as yet unexplained, potential vorticity control exerted by the strait on the basin. Exploration of this mechanism will be the starting point for this research. The proposed experiments will be conducted on the WHOI GFD Laboratory one- and two-meter turntables with tanks containing an upstream basin and a passage to a small catch basin. The work will first explore flows of water under air to permit investigation of flows with relatively small viscous effects in both the upstream basin and strait. It is also planed to pump salty water under a deep layer of fresher water (reduced-gravity configuration), where both increased rotational effects and the role of increased frictional effects in the upstream basin can be explored. Experiments with two active layers may be examined at later stages of the work. Various upstream geometric conditions will be investigated (e.g., flat and bowl-shaped basins) and the role of different mass source characteristics (e.g., boundary inflow and interior downwelling). In all cases layer depths and velocity distributions (with particle imaging techniques) will be measured within both the basin and passage for a wide range of relevant parameters. The experimental work will be parallel to, and compared with, similar theoretical and numerical work already underway at WHOI. Broader Impacts: Deep passages offer ideal points to monitor the overturning circulation. However, this can only be done properly if the dynamical connections between strait and basin flows are understood. This work will begin to answer some of these questions and should be of wide interest beyond the specific dynamics explored here. The PIs are both active in the MIT/WHOI Joint Program and the results of this research will quickly reach the classroom. The grant will also support a graduate student and so further contribute to broader educational goals. Lastly, the grant will generally support the WHOI Geophysical Fluid Dynamics Laboratory, one of few facilities of its type in the world. The WHOI GFD Lab has a long history of helping scientists and students from WHOI and around the world conduct experimental work on a broad range of fluid dynamics problems.