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首页> 外文期刊>Journal of the Atmospheric Sciences >An evaluation of the scale at which topographical features affect the convective boundary layer using large eddy simulations
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An evaluation of the scale at which topographical features affect the convective boundary layer using large eddy simulations

机译：使用大涡模拟评估地形特征影响对流边界层的尺度

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The major objective of this study was to evaluate at which scale topography starts to significantly affect the mean characteristics and structure of turbulence in the convective boundary layer (CBL). The large eddy simulation option of the Regional Atmospheric Modeling System developed at Colorado State University was used for that purpose. It is found that turbulence is nonlinearly dependent on the scale of the topographical features. At a horizontal length scale of less than about 5 km, topography has very little impact on the mean properties of the CBL, even with hills as high as 30% of the height of the CBL. However, it has a significant impact on the organization of the eddies. At larger horizontal scales, topographical features as small as about 10% of the height of the CBL have some effect on the mean characteristics of the CBL. In particular a pronounced impact on the "dispersion" statistics (i.e., horizontal and vertical velocity variances and higher moments) is noticed. Furthermore. the mean turbulence kinetic energy profile depicts two maxima, one near the ground surface and one near the top of the CBL, corresponding to the strong horizontal flow that develops near the ground surface and the return flow at the top of the CBL resulting from the organization of eddies into rolls. The larger the sensible heat Aux fueling the CBL at the ground surface, the less important this impact is. It is concluded that in a very irregular terrain, where topography presents a vertical scale of at least 200-400 m, and a horizontal scale larger than about 5 km, CBL parameterizations of turbulence currently employed in mesoscale and large-scale atmospheric models (e.g., general circulation models), as well as in dispersion models, need to be improved. [References: 34]
机译：这项研究的主要目的是评估在哪个尺度上地形开始显着影响对流边界层（CBL）的平均特征和湍流结构。为此，使用了科罗拉多州立大学开发的区域大气建模系统的大型涡流模拟选项。发现湍流非线性地取决于地形特征的尺度。在小于约5 km的水平长度尺度上，地形对CBL的平均性能影响很小，即使丘陵高达CBL高度的30％。但是，它对涡流的组织有重大影响。在较大的水平比例上，低至CBL高度约10％的地形特征会对CBL的平均特性产生一定影响。特别地，注意到对“分散”统计量（即，水平和垂直速度变化以及更高的力矩）的显着影响。此外。平均湍流动能分布描绘了两个最大值，一个在地面附近，一个在CBL顶部附近，对应于在地面附近发展的强大水平流和在CBL顶部的回流，这是由于组织涡流成卷。在地面上为CBL供能的显热Aux越大，这种影响就越不重要。结论是，在非常不规则的地形中，地形的垂直尺度至少为200-400 m，水平尺度大于约5 km，目前在中尺度和大规模大气模型中使用的CBL湍流参数化（例如，一般流通模型）以及分散模型中的数据需要改进。 [参考：34]

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