Variable Physical Drivers of Near‐Surface Turbulence in a Regulated River
Variable Physical Drivers of Near‐Surface Turbulence in a Regulated River
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DOI：
10.1029/2020wr027939
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发表时间：
2021-11
影响因子：
5.4
通讯作者：
S. Guseva;M. Aurela;A. Cortés;R. Kivi;E. Lotsari;S. Macintyre;I. Mammarella;A. Ojala;V. Stepanenko
中科院分区：
文献类型：
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作者：
S. Guseva;M. Aurela;A. Cortés;R. Kivi;E. Lotsari;S. Macintyre;I. Mammarella;A. Ojala;V. Stepanenko
内陆沃茨，如湖泊、水库和河流，是气候强迫痕量气体的重要来源。调节水和大气之间气体交换的一个关键参数是气体传输速度，其本身由水中近表面湍流控制。而在湖泊和水库中，近地表湍流主要由大气强迫驱动，在浅水河流和溪流中，它是由重力强迫流动的底部摩擦产生的。大型河流代表了这两种情况之间的过渡。在河流中很少测量近地表湍流，湍流的驱动因素也没有量化。我们分析了连续测量的流速和量化湍流的湍流动能耗散率在无冰的季节在一个大的调节河流在北方芬兰。测量的耗散率与整体参数的预测一致，包括平均流速、风速、表面热通量和一维数值湍流模型。数值范围为10− 10 m2 s −3至10− 5 m2 s −3。大气强迫或重力是近地表湍流的主要驱动因素，时间相似。当水流速度受到下游大坝运行的强烈影响时，近地表耗散率在昼夜时间尺度上发生较大的变化。通过结合河床和气水界面边界层湍流的标度关系，我们推导出一个简单的模型，用于估计风速和河流底部摩擦力随深度的相对贡献。
Inland waters, such as lakes, reservoirs and rivers, are important sources of climate forcing trace gases. A key parameter that regulates the gas exchange between water and the atmosphere is the gas transfer velocity, which itself is controlled by near‐surface turbulence in the water. While in lakes and reservoirs, near‐surface turbulence is mainly driven by atmospheric forcing, in shallow rivers and streams it is generated by bottom friction of gravity‐forced flow. Large rivers represent a transition between these two cases. Near‐surface turbulence has rarely been measured in rivers and the drivers of turbulence have not been quantified. We analyzed continuous measurements of flow velocity and quantified turbulence as the rate of dissipation of turbulent kinetic energy over the ice‐free season in a large regulated river in Northern Finland. Measured dissipation rates agreed with predictions from bulk parameters, including mean flow velocity, wind speed, surface heat flux, and with a one‐dimensional numerical turbulence model. Values ranged from ∼10−10m2s−3 to 10−5m2s−3 . Atmospheric forcing or gravity was the dominant driver of near‐surface turbulence for similar fraction of the time. Large variability in near‐surface dissipation rate occurred at diel time scales, when the flow velocity was strongly affected by downstream dam operation. By combining scaling relations for boundary‐layer turbulence at the river bed and at the air‐water interface, we derived a simple model for estimating the relative contributions of wind speed and bottom friction of river flow as a function of depth.