Coherent Structures and Mixing at a River Plume Front
Coherent Structures and Mixing at a River Plume Front
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河流羽流前沿的相干结构和混合
DOI：
10.1002/9781118527221.ch23
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
D. MacDonald
中科院分区：
文献类型：
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作者：
A. Horner‐Devine;C. Chickadel;D. MacDonald
尽管对重力流的动力学和混合进行了多年的研究，但在地球物理尺度上的详细观测相对较少。在本章中，我们给出了锋面传播的测量结果，以及锋面湍流和混合的分布和结构。测量是使用一种新型平台进行的，该平台由一个安装在气球上的红外摄像机和一个安装在容器上的电导率温度传感器链组成。采样船被故意困在汇聚锋中，并在退潮期间跟随它向海航行了近三个小时，以便测量结果固定在锋的参考框架中。在该模式下，对红外图像进行处理，生成高分辨率的锋面速度场和湍流场，并采用控制体积法对锋面混合进行估计。根据湍流动能（TKE）的衰减和TKE耗散率(e)，我们在锋面附近确定了一个大约16 m的高架混合带。锋面混合区域在水面上以相对较冷的水的上涌条纹为标志，这些条纹从锋面向陆地延伸。在锋面上观察到裂片和裂缝，这是实验室实验中观察到的重力流的特征。湍流是在叶和间隙的环流中组织起来的，叶的耗散率比周围锋面区域的耗散率高一个数量级。
Despite years of research on the dynamics and mixing of gravity currents, there are relatively few detailed observations at geophysical scales. In this chapter, we present measurements of the frontal propagation, and distribution and structure of frontal turbulence and mixing, at a river plume front. The measurements are made using a novel platform that consists of a balloon-mounted infrared camera in combination with a vessel-mounted conductivitytemperature sensor chain. The sampling vessel was deliberately trapped in the convergent front, and followed it seaward for almost three hours during the ebb tide, so that the measurements were fixed in the frame of reference following the front. In this mode, the infrared images have been processed to generate high-resolution frontal velocity and turbulence fields, and a control volume approach is used to estimate the frontal mixing. We identify an approximately 16 m band of elevated mixing near the front based on the decay of turbulent kinetic energy (TKE) and TKE dissipation rate (e). This region of frontal mixing is marked on the water surface by upwelling streaks of relatively cool water that extend landward from the front. Lobes and clefts were observed along the front that are characteristic of gravity currents observed in laboratory experiments. Turbulence is organized within the circulation of the lobes and clefts, with dissipation rates in the lobes being an order of magnitude higher than in the surrounding frontal regions.