A nonlocal three‐dimensional turbulence parameterization (NLT 3D ) for numerical weather prediction models
A nonlocal three‐dimensional turbulence parameterization (NLT 3D ) for numerical weather prediction models
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DOI：
10.1002/qj.4195
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发表时间：
2021-10
影响因子：
8.9
通讯作者：
V. Kuell;Andreas Bott
中科院分区：
文献类型：
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作者：
V. Kuell;Andreas Bott
随着数值天气预报(NWP)模式分辨率的提高，经典的次网格尺度过程在模式网格上的分辨率越来越高。特别是，行星边界层(PBL)中的湍流在垂直方向上已经部分地在当代模型中得到了解决。对于经典的局部PBL格式，所产生的上梯度热传输不能被正确处理。因此，过去已经开发了非局部湍流格式。当数值预报模式的水平网格尺寸小于几公里时，边界层中的大湍流涡旋也将开始在水平方向上部分分解。描述非局部湍流交换的一种非常灵活的方法是传递矩阵法，该方法被用来发展一种新的湍流参数化方法。由此产生的NLT 3D方案将瞬变混合矩阵应用于所有三个维度的次网格尺度的传输。我们将WRF实况模拟的结果与均匀地形(Case-99)和复杂地形(CAPTEX)上的现场观测结果进行了比较，其中包括我们的方案、经典的局部湍流方案(Mynn)和现有的非局部一维方案(ACM2)。在均匀地形上，三种方案都能很好地捕捉到观测到的地表通量和探空仪剖面，而在复杂地形上，差异变得更加明显。在阿巴拉契亚山区的示踪剂释放实验(CAPTEX)中，PBL的混合和垂直程度对重现观测到的示踪剂标记气团的平流速度是决定性的。更深的混合不仅加速了地面风，还使示踪剂在高海拔地区移动得更快，然后混合回地面。正如只有标准水平斯马戈林斯基扩散(NLT 1D)的NLT 3D版本的结果表明，在水平网格大小为几公里的情况下，模拟三维湍流可能已经是有益的。
With increasing resolution of numerical weather prediction (NWP) models, classical subgrid‐scale processes become increasingly resolved on the model grid. In particular, turbulence in the planetary boundary layer (PBL) is vertically already partially resolved in contemporary models. For classical local PBL schemes, resulting up‐gradient heat transports cannot be treated correctly. Thus, nonlocal turbulence schemes have been developed in the past. As the horizontal grid sizes of NWP models become smaller than a few kilometers, the large turbulence eddies in the PBL will also start to become partially resolved in the horizontal direction. A very flexible way to formulate nonlocal turbulent exchange is the transilient matrix method, which is used here to develop a new turbulence parameterization. The resulting NLT 3D scheme applies transilient mixing matrices to subgrid‐scale transports in all three dimensions. We compare results of WRF real‐case simulations including our scheme, a classical local turbulence scheme (MYNN), and an existing nonlocal one‐dimensional scheme (ACM2) with observations from field campaigns over homogeneous terrain (CASES‐99) and complex terrain (CAPTEX). Over homogeneous terrain, all three schemes similarly well capture the observed surface fluxes and radiosonde profiles, whereas over complex terrain more differences become obvious. During a tracer release experiment (CAPTEX) over the Appalachian mountain region, the mixing and vertical extent of the PBL turn out to be decisive to reproduce the observed advection speed of the tracer‐marked air mass. Deeper mixing not only accelerates surface winds but also enables tracer to travel faster at higher altitudes and then mix back to the ground. As results from a version of NLT 3D with only standard horizontal Smagorinsky diffusion (NLT 1D ) demonstrate, simulating three‐dimensional turbulence can be beneficial already at horizontal grid sizes of a few kilometers.