Driven around the bend: Spatial evolution and controls on the orientation of helical bend flow in a natural submarine gravity current
Driven around the bend: Spatial evolution and controls on the orientation of helical bend flow in a natural submarine gravity current
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DOI：
10.1002/2013jc009008
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发表时间：
2014-02
影响因子：
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通讯作者：
E. Sumner;J. Peakall;R. Dorrell;D. Parsons;S. Darby;R. Wynn;S. McPhail;J. Perrett;A. Webb
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文献类型：
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作者：
E. Sumner;J. Peakall;R. Dorrell;D. Parsons;S. Darby;R. Wynn;S. McPhail;J. Perrett;A. Webb
海底航道系统将大量陆地沉积物输送到深海。了解创建这些系统的重力流的动力学，特别是这些流如何与弯曲相互作用并形成弯曲，对于预测系统架构和演化至关重要。弯曲流的特点是螺旋结构，在河流中通常包括向内的近河床流和向外的近地表流。经过十年的争论，现在人们普遍认为海底航道弯曲处的螺旋流可以表现出多种结构，包括与河流中观察到的相反的结构。新的挑战是了解是什么控制着海底流中螺旋流动池的方向并确定反转的条件。我们提供来自黑海的数据，首次显示活跃海底重力流的三维速度和密度结构。通过计算作用在流动上的力，我们评估控制螺旋流动池方向的因素。我们证明，在控制螺旋流的方向方面，由流道跨层分层引起的径向压力梯度比离心加速度更重要。我们还证明，由于地形强迫和横流流的下游平流而引起的非局部流动加速是动量平衡中的重要项。这些发现对海底航道动力学的概念和数值模型具有重大意义，因为它们表明需要结合跨航道流动分层的三维模型来准确表示此类系统中曲率引起的螺旋流。
Submarine channel systems transport vast amounts of terrestrial sediment into the deep sea. Understanding the dynamics of the gravity currents that create these systems, and in particular how these flows interact with and form bends, is fundamental to predicting system architecture and evolution. Bend flow is characterized by a helical structure and in rivers typically comprises inwardly directed near-bed flow and outwardly directed near-surface flow. Following a decade of debate, it is now accepted that helical flow in submarine channel bends can exhibit a variety of structures including being opposed to that observed in rivers. The new challenge is to understand what controls the orientation of helical flow cells within submarine flows and determines the conditions for reversal. We present data from the Black Sea showing, for the first time, the three-dimensional velocity and density structure of an active submarine gravity current. By calculating the forces acting on the flow we evaluate what controls the orientation of helical flow cells. We demonstrate that radial pressure gradients caused by across-channel stratification of the flow are more important than centrifugal acceleration in controlling the orientation of helical flow. We also demonstrate that non-local acceleration of the flow due to topographic forcing and downstream advection of the cross-stream flow are significant terms in the momentum balance. These findings have major implications for conceptual and numerical models of submarine channel dynamics, because they show that three-dimensional models that incorporate across-channel flow stratification are required to accurately represent curvature-induced helical flow in such systems.