NLT3D: a non-local three-dimensional turbulence parameterization scheme for next generation numerical weather prediction models

数值天气预报模式必须将大气过程分成两类：空间尺度上大于网格尺度的过程可以用基本方程(守恒定律)显式模拟，而次网格尺度的过程必须用物理参数化方案来表示。随着计算机能力的增强，许多国家预报中心现在的目标是在未来几年内投入运营的千米和亚千米范围内的水平电网规模。由于预报模式中使用的大多数参数化方案都是针对几公里或更长的水平网格尺寸开发的，因此它们的表述和所包括的过程的选择将成为问题。这一点对于表示亚网格尺度动力学和主要在行星边界层(PBL)中的输送的湍流参数化来说尤其适用。由于这里发生了能量、动量、水汽和其他微量气体与地球表面的交换，因此对PBL过程的正确模拟对于良好的预报质量是至关重要的。由于边界层中能量最大的大涡不能用经典的K方法来模拟小涡旋的局部混合，非局地(但仍然是一维)湍流格式被发展来考虑较小的垂直网格尺寸。另一方面，水平方向上的小网格尺寸现在也要求网格箱之间的水平湍流交换的表示，即三维湍流的模拟。为了克服这些问题，我们计划通过水平湍流交换来扩展现有的非局部一维湍流参数化，从而发展一种三维湍流的非局部参数化方案。作为我们方案开发和测试的模型环境，我们将使用来自美国UCAR/NCAR的WRF模型。然而，该方案中的算法将以一种允许在其他高分辨率预测模型中实施的方式来制定。

Numerical weather prediction models have to split the atmospheric processes into two classes: processes on spatial scales larger than the grid size can be simulated explicitly by the basic equations (conservation laws), while subgrid scale processes have to be represented by physical parameterization schemes. With increasing computer power many national forecast centers now aim at horizontal grid sizes in the kilometer and subkilometer range to be operationally available in the next years. Since most parameterization schemes used in forecast models have been developed for horizontal grid sizes of several kilometers and more, their formulation and selection of processes included will then become questionable. This holds especially for the turbulence parameterization representing subgrid scale dynamics and transport mainly in the planetary boundary layer (PBL). Since here the exchange of energy, momentum, moisture and other trace gases with the earth's surface takes place, a correct simulation of the PBL processes is decisive for a good forecast quality. Since the most energetic large eddies in the boundary layer cannot be represented by classical K approaches simulating local mixing by small eddies, non-local (but still one-dimensional) turbulence schemes have been developed to account for smaller vertical grid sizes. On the other hand, small grid sizes in the horizontal direction now also claim the representation of horizontal turbulent exchange between the grid boxes, i.e. the simulation of three-dimensional (3D) turbulence. To overcome these problems, we plan to develop a non-local parameterization scheme for 3D turbulence by extending an existing non-local one-dimensional turbulence parameterization by a horizontal turbulent exchange. As a model environment for development and testing of our scheme we will use the WRF model from UCAR/NCAR, USA. However, the algorithms in the scheme will be formulated in a way allowing for implementation in other high resolution forecasting models as well.