Accurately predicting bare-soil evaporation requires the proper characterization of the near-surface atmospheric conditions. These conditions, dependent on factors such as surface microtopography and wind velocity, vary greatly and therefore require high-resolution datasets to be fully incorporated into evaporation models. These factors are oftentimes parameterized in models through the aerodynamic resistance (r_a), in which the vapor roughness length (z_0v) and the momentum roughness length (z_0m) are two crucial parameters that describe the transport near the soil-atmosphere interface. Typically, when evaluating bare-soil evaporation, these two characteristic lengths are assumed equal, although differences are likely to occur especially in turbulent flows over undulating surfaces. Thus, this study aims to investigate the relationship between z_0v and z_0m above undulating surfaces to ultimately improve accuracy in estimating evaporation rate. To achieve this goal, four uniquely designed wind tunnel—soil tank experiments were conducted considering different wind speeds and undulation spacings. Particle image velocimetry (PIV) was used to measure the velocity field above the undulating surface in high resolution. Using the high-fidelity data set, the logarithmic ratio of z_0v to z_0m is determined and used to estimate r_a. Results confirm that these lengths differ significantly, with the logarithmic ratio roughly ranging from −15 to −5 under the conditions tested. PIV-measured results demonstrate this ratio is closely tied to the mass and momentum transport behaviors influenced by surface undulations. Using the data-integrated formulation of r_a, predictions of evaporation rate were prepared for both the laboratory and lysimeter experiments, demonstrating the efficacy of the proposed approach in this study.

中文翻译：

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基于 PIV 测得的速度剖面确定起伏土壤表面上方的蒸汽和动量粗糙度长度

准确预测裸土蒸发需要对近地表大气条件进行适当的表征。这些条件取决于表面微地形和风速等因素，变化很大，因此需要将高分辨率数据集完全纳入蒸发模型。这些因素通常通过空气动力阻力 ( r _a )在模型中参数化，其中蒸汽粗糙度长度 ( z _0v ) 和动量粗糙度长度 ( z _{0m )}) 是描述土壤-大气界面附近传输的两个关键参数。通常，在评估裸土蒸发时，假设这两个特征长度相等，尽管可能会出现差异，尤其是在起伏表面上的湍流中。因此，本研究旨在研究z _0v和z _0m之间的关系。以最终提高估计蒸发率的准确性。为了实现这一目标，考虑到不同的风速和起伏间距，进行了四个设计独特的风洞-土壤罐实验。粒子图像测速仪 (PIV) 用于以高分辨率测量起伏表面上方的速度场。使用高保真数据集，确定z _0v与z _0m的对数比并用于估计r _a. 结果证实这些长度存在显着差异，在测试条件下对数比大致范围从 -15 到 -5。PIV 测量结果表明该比率与受表面起伏影响的质量和动量传输行为密切相关。使用r _a的数据集成公式，为实验室和蒸渗仪实验准备了蒸发率的预测，证明了所提出的方法在本研究中的有效性。