This paper investigated the integral length scales of turbulence in a low-roughness atmospheric surface layer (ASL), characterised by very smooth terrain in the Utah desert during near-neutral conditions, and evaluated the Engineering Sciences Data Unit (ESDU) 85020 and 86010 predictions for the turbulence length scales in a low-roughness ASL. The correlation integral method was used to estimate the integral length scales of the velocity components with longitudinal, lateral and vertical separations from sonic measurements on a vertical tower and spanwise array in the Surface Layer Turbulence and Environmental Science Test (SLTEST) field experiment. It was found that the longitudinal integral length scales calculated using near-neutral SLTEST data followed a logarithmic relationship with height proportional to the mean velocity profile with approximately constant integral time scale, however the sizes of the longitudinal components of the energy-containing eddies in the low-roughness flat terrain were 2–3 times smaller than those previously measured during field experiments in open country terrains. The calculated length scales with longitudinal separations over the very smooth terrain characteristics of the salt flats at Dugway were not consistent with those predicted by ESDU 85020. In contrast, the scaling of the lateral and vertical components of the three-dimensional turbulence structure with respect to the longitudinal component in the low-roughness ASL were consistent with similarity theory predictions in ESDU 86010 that the scaling ratios are independent of terrain roughness. Furthermore, this confirms the large dependence of the longitudinal turbulence length scales on the upstream terrain roughness and highlights the large variation of turbulence length scales observed at different low-roughness sites in the literature.

中文翻译：

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低粗糙度近中性大气表面层中的湍流长度比例

本文研究了低粗糙度大气表层 (ASL) 中湍流的积分长度尺度，其特征是在近中性条件下犹他州沙漠中地形非常平滑，并评估了工程科学数据单元 (ESDU) 85020 和 86010 的预测用于低粗糙度 ASL 中的湍流长度尺度。在表层湍流和环境科学测试 (SLTEST) 现场实验中，相关积分方法用于从垂直塔和展向阵列上的声波测量中估计具有纵向、横向和垂直分离的速度分量的积分长度尺度。发现使用近中性 SLTEST 数据计算的纵向积分长度尺度遵循对数关系，高度与平均速度剖面成正比，积分时间尺度近似恒定，然而低粗糙度平坦地形比以前在开阔地区地形的现场实验中测量的要小 2-3 倍。在 Dugway 盐滩非常平滑的地形特征上计算出的具有纵向间隔的长度尺度与 ESDU 85020 的预测不一致。 相反，三维湍流结构的横向和垂直分量相对于低粗糙度 ASL 中的纵向分量的缩放与 ESDU 86010 中的相似理论预测一致，即缩放比例与地形粗糙度无关。此外，这证实了纵向湍流长度尺度对上游地形粗糙度的很大依赖性，并突出了文献中在不同低粗糙度地点观察到的湍流长度尺度的巨大变化。