Eddy correlation flux measurements: The sediment surface area that contributes to the flux
Eddy correlation flux measurements: The sediment surface area that contributes to the flux
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DOI：
10.4319/lo.2007.52.4.1672
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发表时间：
2007-07-01
影响因子：
4.5
通讯作者：
Wiberg, Patricia L.
中科院分区：
文献类型：
--
作者：
Berg, Peter;Roy, Hans;Wiberg, Patricia L.
我们调查的大小和形状的沉积物表面上的区域，所谓的足迹，有助于通量在水下涡动相关测量。示踪剂跟踪模拟进行了溶解的保守示踪剂从沉积物表面释放到电流驱动的流不受密度分层和表面波。模拟结果表明，足迹长度（l）可以计算为l = -2.783 - 158.7h +159.2h（2）- 120.8h log（z（0））（所有单位均为m），对于涡动相关测量，高度（h）在沉积物表面以上0.05至0.3 m之间，对于沉积物表面粗糙度参数（z（0））值在7.04 x 10（-6）和0.01 m.到贡献最强通量信号的位置的上游距离（x（max））同样可以被估计为x（max）= -0.09888-11.53h +10.25h（2）-6.650h log（z（0））。由于垂直湍流混合尺度与平均流速有关，l和x（max）与流速无关。足迹宽度（w）可计算为w = 6.531h。这些表达式适用于水深（H）> 27 h的情况。在深度区间6.7h < H <27 h中，l可以通过将上述长度乘以因子1 + 8.347exp（-0.2453 H/h）来计算，而x（max）与H无关。当H < 6.7h时，示踪剂在气-水界面上的迁移速率控制着足迹的大小和形状。所有表达式对各向同性湍流都是有效的，但作为一阶估计，l和x（max）的表达式也适用于各向异性条件。相比之下，w与根E-y / E-z成比例，其中E-y和E-z分别是横向和垂直涡动扩散率。最后，我们描述了如何现场特定的值z（0）和水平的各向异性的湍流近底流可以直接从涡动相关测量提取。
We investigated the size and shape of the area on the sediment surface, the so-called footprint, that contributes to the flux in subaqueous eddy correlation measurements. Tracer tracking simulations were performed for a dissolved conservative tracer released from the sediment surface into a current-driven flow not affected by density stratifications and surface waves. Simulations revealed that the footprint length (l) can be calculated as l = -2.783 - 158.7h + 159.2h(2) - 120.8h log(z(0)) (all units in m) for eddy correlation measurements heights (h) between 0.05 and 0.3 m above the sediment surface and for sediment surface roughness parameter (z(0)) values between 7.04 x 10(-6) and 0.01 m. The upstream distance (x(max)) to the location that contributes the strongest flux signal can likewise be estimated as x(max) = -0.09888 - 11.53h + 10.25h(2) - 6.650h log (z(0)). Because vertical turbulent mixing scales with mean current velocity, l and x(max) are independent of current velocity. The footprint width (w) can be calculated as w = 6.531h. These expressions were developed for water depths (H) of H > 27h. In the depth interval 6.7h < H < 27h, l can be calculated by multiplying the length, as given above, by the factor 1 + 8.347exp(- 0.2453 H/h), whereas x(max) is independent of H. For H < 6.7h, the tracer transfer rate over the air-water interface controls the size and shape of the footprint. All expressions are valid for isotropic turbulence, but as a first-order estimate, the expressions for l and x(max) also hold for anisotropic conditions. In contrast, w scales with root E-y / E-z, where E-y and E-z are the transverse and the vertical eddy diffusivity, respectively. Finally, we describe how site-specific values of z(0) and levels of anisotropy in a turbulent near-bottom flow can be extracted directly from eddy correlation measurements.