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）显示了海峡流的随时间变化的稳定分量，以及下游混合的各个方面。 然而，对供给海峡的水流结构以及海峡水流如何与上游流域环流耦合的了解却少得多。 其次，最近的理论和数值研究提出了一种新的耦合机制，但没有观测数据和实验室实验数据来测试和推广这些新想法。 理论与实验室实验之间的拟议比较可用于建议未来的海洋观测和可能的溢流监测策略。 其目的是提供尽可能多的信息，以指导未来的海洋巡航，大气环流理论，和数值气候模拟projectsLaboratory实验室的实验将开发和进行调查的耦合在一个有限的，旋转的盆地与水力控制的流在一个窗台。这种情况通常适用于从一个充满深水的深海盆地通过山坳或最深的鞍点通道到达另一个盆地的深水层。在下游流域，水的密度通常较低。 目标是获得定量测量，以检查盆地环流，包括任何馈线电流，耦合盆地海峡系统的位涡动力学，以及海峡中的水力流量。最近的一项数值研究表明，海峡对海盆施加了一种新颖的、尚未解释的位涡控制。探索这一机制将是本研究的出发点。 拟议的实验将在WHOI GFD实验室的一米和两米转盘上进行，转盘上装有一个上游水池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，以便调查上游盆地和海峡中粘性效应相对较小的水流。还计划在较淡水的深层下泵送盐水（重力降低配置），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。两个活性层的实验可能会在工作的后期阶段进行检查。将研究各种上游几何条件（例如， 平坦和碗状盆地）和不同质量源特征的作用（例如， 边界流入和内部下降流）。 在所有情况下，将在盆地和通道内测量层深和速度分布（使用粒子成像技术），以获得广泛的相关参数。实验工作将与WHOI已经在进行的类似理论和数值工作平行并进行比较。 更广泛的影响：深通道提供了理想的点，以监测翻转环流。然而，这只能做得很好，如果海峡和流域流量之间的动态连接的理解。 这项工作将开始回答其中的一些问题，应该是广泛的兴趣超出了这里探讨的具体动态。 PI都活跃在麻省理工学院/WHOI联合计划，这项研究的结果将很快到达教室。该补助金还将支持研究生，从而进一步促进更广泛的教育目标。最后，赠款将用于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。WHOI GFD实验室在帮助WHOI和世界各地的科学家和学生就广泛的流体动力学问题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.