A Length Scale Defining Partially-Resolved Boundary-Layer Turbulence Simulations
A Length Scale Defining Partially-Resolved Boundary-Layer Turbulence Simulations
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DOI：
10.1007/s10546-013-9881-3
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发表时间：
2014-04-01
影响因子：
4.3
通讯作者：
Beare, Robert J.
中科院分区：
文献类型：
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作者：
Beare, Robert J.
数值天气预报(NWP)模式预报现在可以在100米到1公里的水平网格长度范围内进行。在这个网格长度范围内，对流边界层(CBL)被部分分解，因此处于所谓的“灰色区域”。对于灰色区域的模拟，来自平流方案和次网格模式的数值耗散源可能是重要的。到目前为止，这些影响还没有完全纳入我们对灰色地带的理解。为了量化这些影响，定义了一个基于湍动能谱二阶矩的耗散长度尺度。使用大涡模式对CBL进行了一系列模拟，包括灰区分辨率和一系列子格子模式、平流方案和垂直格子配置。耗散长度尺度区分了灰色区域内不同模式配置的影响。在边界层中部，数值耗散对分解的TKE有很强的控制作用。这导致了利用耗散长度尺度在灰色区域中解析的TKE的相似律。在逆温深度和耗散长度尺度相同的情况下，出现了灰色区域的新定义。这与使用水平网格长度的典型定义形成对比。然而，在逆温中，耗散长度尺度随网格长度的变化是不可预测的，这反映了在灰色区域模拟卷吸的重大挑战。因此，耗散长度尺度是一种简单的诊断方法，可以帮助数值预报和大涡模式人员理解灰色区域。
Numerical weather prediction (NWP) model forecasts at horizontal grid lengths in the range of 100 m to 1 km are now possible. Within this range of grid lengths, the convective boundary layer (CBL) is partially resolved and thus in the so-called 'grey zone'. For simulations in the grey zone, numerical dissipation sources from both the advection scheme and the subgrid model are likely to be significant. Until now, these effects have not been incorporated fully into our understanding of the grey zone. In order to quantify these effects, a dissipation length scale is defined based on the second moment of the turbulent kinetic energy (TKE) spectrum. An ensemble of simulations of a CBL are performed using a large-eddy model across the grey-zone resolutions and for a range of subgrid model, advection scheme and vertical grid configurations. The dissipation length scale distinguishes the effects of the different model configurations in the grey zone. In the middle of the boundary layer, the resolved TKE is strongly controlled by the numerical dissipation. This leads to a similarity law for the resolved TKE in the grey zone using the dissipation length scale. A new definition of the grey zone emerges where the inversion depth and dissipation length scale are the same size. This contrasts with the typical definition using the horizontal grid length. At the inversion, however, the variation of the dissipation length scale with grid length is less predictable, reflecting significant challenges for modelling entrainment in the grey zone. The dissipation length scale is thus a simple diagnostic to aid both NWP and large-eddy modellers in understanding the grey zone.