Analytical and Numerical Studies of Deep Overflows and Related Circulations

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Intellectual Merit:This project seeks to extend our current understanding of deep overflows through a comprehensive study of rotating hydraulics of two-layer sill flows connected to broad basins. Two-layer dynamics are thought to be important in the overflows of a number of important passages, including the Denmark Strait, the Faroe-Bank Channel, and the Vema Channel, either in accounting for the influence of reverse flows at the surface or the evolution of distinct water masses feeding the channel and contained within the overflows. This study brings analytical and numerical techniques to bear on a number of fundamental issues including the dynamically consistent connection of two-layer hydraulic theory to the neighboring basin flows for both exchange and unidirectional flow cases, aspiration of deep layers, general methods for the identification of hydraulic control and the isolation of special features such as hydraulic jumps in channels with arbitrary cross section, and the role of time-dependence in straits and coupled basin-strait systems. The elucidation of these issues will aid in the interpretation of results from more complicated numerical models, observations, and in the planning of strategies for long-term monitoring of overflow transport from within upstream basins. Also, the investigators will continue to find ways of presenting the results so as to favor the intuition and to be accessible to the non-specialist. Broader Impacts:Deep passages offer ideal points to monitor the overturning circulation. However, this can only be done properly after development of hydraulic theories with improved realism and once 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 two investigators are both active in the MIT/WHOI Joint Program and the results of this research will quickly reach the classroom. A small percentage of the grant will support the completion of a graduate text on ocean strait and sill flow and other applications of hydraulics in geophysics. The grant will also provide continuing support for a graduate student to complete his thesis.