摘要:为研究黄河源区边界层湍流特征及其对物质和能量输送的影响，本文首次采用大涡模拟的方法，对比分析了黄河源区两种不同下垫面上（鄂陵湖和湖边草地）对流边界层（CBL）中精细的湍流结构特征。使用资料为2012年夏季黄河源区鄂陵湖流域野外观测实验的GPS探空资料、涡动相关观测资料。分析表明，模拟的黄河源区草地和湖上CBL的平均结构与实测结果吻合较好，但草地和湖上CBL的湍流结构特征差异较明显。模拟结果显示，草地CBL内湍能收支、湍流特征量的时空分布和湍涡结构特征均与陆地上热力驱动CBL的研究结果一致；湖上CBL顶部存在明显的对流卷特征，且夹卷层的湍流强度比草地的强，而草地近地面湍强则更大。通过改变水平分辨率的模拟试验，发现两个不同下垫面上模拟结果对模式分辨率的敏感性不同，湖面CBL的模拟要选择较高的水平分辨率（50～100 m），以提高近湖面和夹卷层对湍流动能和湍流通量模拟的精度，也充分模拟出各种尺度的波对湍流通量的累积贡献。考虑到计算时间等影响，模拟草地边界层精细的湍流结构时建议选择网格距为100～200 m。
关键词:黄河源区/
对流边界层/
湍流结构/
大涡模拟/
水平分辨率
Abstract:In order to study the turbulent characteristics of the boundary layer and its effects on the transport of momentum, heat, and water vapor in the Source Region of the Yellow River (SRYR), northeast of the Tibetan Plateau, large eddy simulations are performed for the first time to investigate the fine structure of turbulence in the convective boundary layer (CBL) over two different underlying surfaces (grassland and lake) in the SRYR. GPS soundings and eddy covariance data observed during a field experiment in the Ngoring Lake Basin in summer 2012 are used. It shows that the averaged structures of CBLs over the grassland and lake are in good agreement with the observations, but the characteristics of the turbulent structures over both surfaces show large differences. The budget of turbulent energy, spatial-temporal distribution of turbulent properties, and the structural features of turbulent eddies above the grassland are consistent with the thermal-driven CBL over the land. Organized convective rolls presented at the top of the CBL over the lake. There is larger turbulent intensity at the top of CBL over the lake due to strong entrainment, while the same occurs in the surface layer over the grassland. It is found that the simulated results are sensitive to the horizontal resolution over both surfaces. The denser horizontal resolution applied over the lake helps to improve accuracy in simulation of turbulent kinetic energy and turbulent fluxes of the surface layer and the entrainment layer, and the contributions of various scale’s waves to turbulent fluxes are fully simulated as well. The grid spacings of 100–200 m are recommended to simulate the fine turbulent structure over the grassland if the simulated time is considered.
Key words:SRYR/
CBL/
Turbulent structure/
Large eddy simulation/
Horizontal resolution
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