An Assessment of the Importance of Chaotic Stirring and Turbulent Mixing on the West Florida Shelf
An Assessment of the Importance of Chaotic Stirring and Turbulent Mixing on the West Florida Shelf
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DOI：
10.1175/2009jpo4046.1
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发表时间：
2009-07-01
影响因子：
3.5
通讯作者：
Olascoaga, M. J.
中科院分区：
文献类型：
--
作者：
Beron-Vera, F. J.;Olascoaga, M. J.
最近，动力系统工具的应用在混合坐标海洋模式(HYCOM)模拟产生的表层洋流中揭示了在西佛罗里达陆架(WFS)南部存在持续的大尺度拉格朗日相干结构(LCS)。与卫星跟踪的漂流物轨迹一致，这种LCS构成了被动示踪剂横向运输的跨陆架屏障。由于上述LCS以及位于岸边的较小尺度LCS可能对污染物扩散及其潜在的非常重要的生物后果施加限制，因此对WFS上表层海洋拉格朗日运动的性质进行了研究。该分析的基础是能够维持上述持续跨陆架运输障碍的相同的模拟表层海洋速度场。对几种诊断方法的研究表明，在长达两个月左右的时间尺度上，混沌搅拌主导着湍流混合。更具体地说，在这些时间尺度上发现，在给定的长度尺度上，示踪剂的演化在一定程度上受较粗尺度的速度场特征的支配，流体颗粒的弥散在空间上是不均匀的，拉格朗日演化比驱动欧拉流更不规则。
Application of dynamical systems tools has recently revealed in surface ocean currents produced by a Hybrid-Coordinate Ocean Model ( HYCOM) simulation the presence of a persistent large-scale Lagrangian coherent structure ( LCS) on the southern portion of the west Florida shelf ( WFS). Consistent with satellite-tracked drifter trajectories, this LCS constitutes a cross-shelf barrier for the lateral transport of passive tracers. Because of the constraints that the above LCS, as well as smaller-scale LCSs lying shoreside, can impose on pollutant dispersal and its potentially very important biological consequences, a study was carried out on the nature of the surface ocean Lagrangian motion on the WFS. The analysis is based on the same simulated surface ocean velocity field that has been able to sustain the aforementioned persistent cross-shelf transport barrier. Examination of several diagnostics suggests that chaotic stirring dominates over turbulent mixing on time scales of up to two months or so. More specifically, it is found on those time scales that tracer evolution at a given length scale is governed to a nonnegligible extent by coarser-scale velocity field features, fluid particle dispersion is spatially inhomogeneous, and the Lagrangian evolution is more irregular than the driving Eulerian flow.