Measuring turbulent large-eddy structures with an ADCP. Part 2. Horizontal velocity variance
Measuring turbulent large-eddy structures with an ADCP. Part 2. Horizontal velocity variance
复制标题
使用 ADCP 测量湍流大涡流结构。
DOI：
10.1357/002224009791218823
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发表时间：
2009
影响因子：
0.5
通讯作者：
C. Grosch
中科院分区：
文献类型：
--
作者：
A. Gargett;A. Tejada;C. Grosch
本文考虑声学多普勒流速剖面仪（ADCP）观测确定湍流水平速度方差的准确度。在以前的文件解决湍流垂直速度的变化，我们使用的技术相结合，从简单的理论和海洋观测与VADCP（ADCP与额外的垂直（V）梁）在两个不同的海洋湍流湍流，朗缪尔超单体（LSC）和不稳定对流的响应函数。在LSC的情况下，我们还通过对具有特定艾德梁几何形状的可用大涡模拟（LES）进行采样来确定响应。与以前的研究相比，垂直速度方差的直接测量可从垂直波束的VADCP，我们缺乏直接测量的水平速度方差。因此，这里报告的水平方差的观测响应是一个估计值，取为一阶方差估计值与（假设更准确）二阶方差估计值的比值，这是由于垂直波束的存在而首次成为可能。理论响应函数用于说明水平尺度、垂直/水平各向异性和湍流场大涡可能的准相干相位结构对响应的影响，并预测改变倾斜光束与垂直方向的角度（cid：1）的影响。观测估计表明，对流湍流的特点是近统一响应整个水柱的水平速度的变化，与理论预测一致。对于朗缪尔超胞，理论响应正确地预测了LES导出的响应函数的定性行为，特别是水柱下部的高估向水面转移到低估。LES对不同（cid：1）值的响应也与理论一致：两种方法都表明，（cid：1）（cid：2）30°比（cid：1）（cid：2）20°（目前的商业标准）提供更准确的水平湍流速度变化测量。对于所有检查的
This paper considers the degree of accuracy with which observations from an acoustic Doppler current profiler (ADCP) can determine turbulent horizontal velocity variance. As in a previous paper addressing turbulent vertical velocity variance, we use a combination of techniques, deriving response functions from simple theory and from oceanic observations taken with a VADCP (an ADCP with an additional vertical (V) beam) in two different oceanic turbulent flows, Langmuir supercells (LSC) and unstable convection. In the case of LSC, we also determine response by sampling available Large-Eddy Simulations (LES) with specified beam geometry. In contrast with the previous investigation, where a direct measurement of vertical velocity variance was available from the vertical beam of the VADCP, we lack direct measurements of horizontal velocity variances. Thus the observational response reported here for horizontal variance is an estimate, taken as the ratio of first-order to the (assumed more accurate) second-order variance estimates made possible for the first time by the presence of a vertical beam. The theoretical response function is used to illustrate effects on response of horizontal scale, vertical/horizontal anisotropy and possible quasi-coherent phase structure of the large eddies of the turbulent field, and to predict the impact of changing (cid:1) , the angle of slant beams from vertical. Observational estimates show that convective turbulence is characterized by near-unity response throughout the water column for both horizontal velocity variances, in agreement with theoretical prediction. For Langmuir supercells, theoretical responses correctly predict qualitative behavior of the LES-derived response functions, specifically overestimation in the lower part of the water column shifting to underestimation toward the surface. LES-derived responses for different values of (cid:1) are also in agreement with theory: both approaches suggest that (cid:1) (cid:2) 30° provides more accurate measurement of horizontal turbulent velocity variance than does (cid:1) (cid:2) 20°, the present commercial standard. For all examined