Development of a Coherent Transilient Turbulence and Convection (CTTC) parameterization scheme for use in numerical weather prediction models

通常，在数值天气预报（NWP）模式中，垂直亚网格尺度运动的参数化要么是湍流格式，要么是对流格式。该决定通常基于由浮力或剪切不稳定引起的动力学的预期垂直程度：如果运动的垂直范围很短和/或限于行星边界层（PBL），那么它被湍流方案视为混合事件。在垂直范围更大的情况下，对流方案将运动视为具有云物理、上升和下降气流以及可能的降水的垂直输送。意识到这种分类在本质上没有明显的限制，要求统一或连贯的湍流和对流参数化出现了。提出的项目旨在开发一个统一的、无缝的，即连贯的湍流和对流参数化方案。为了解决这一问题，我们提出了一种结合局部湍流涡旋扩散系数（k -逼近）项和各种非局部湍流和对流羽流的质量通量项的方法。作为一种直观的形式，我们将采用弹性矩阵方法，其中每个矩阵元素量化了某一源层和目标层之间的传输。在我们的项目中，经典的质量通量项将被允许净质量输运的形式所取代。一个核心问题将是，湍流/对流环流何时以及在何种程度上在网格尺度上得到解决。换句话说，什么时候和多少净质量传递是参数化的。根据空间尺度对局部湍流、非局部湍流、浅对流和深对流进行分类，很明显，根据宿主模式的网格大小，可能存在从没有到完全的净质量输运或多或少的平滑过渡。此外，所涉及的物理过程，如热力学、云的形成和降水，必须由物理参数控制，而不是依赖于模型网格的决策。根据网格大小，净质量输运将无缝地考虑到非局部湍流/浅对流的空间状态。由于全局高分辨率的NWP模型对于操作应用来说计算成本太高（并且仍然会如此），NWP必须依赖于模型链或具有在线嵌套的多尺度模型。对于两种可操作的NWP模式，一个相干的、尺度自适应的湍流和对流方案将避免由于预期的动力学空间尺度和当前网格尺度而在不同方案之间进行人为切换。在建议的项目范围内，我们将使用DWD的ICON模型作为开发环境，但将参数化方案保留为通用形式，以便在其他NWP模型中实施。

Usually, in numerical weather prediction (NWP) models vertical subgrid scale motions are either parameterized by a turbulence scheme or a convection scheme. The decision is often based on the expected vertical extent of the dynamics resulting from buoyancy or shear instability: If the motion is of short vertical range and/or confined to the planetary boundary layer (PBL), then it is treated as a mixing event by the turbulence scheme. In case of a more extended vertical range, the motion is treated by the convection scheme as a vertical transport with cloud physics, up- and downdrafts and possibly precipitation. Being aware that there are no sharp limits for such classifications in nature, the claim for a unified or coherent turbulence and convection parameterization arises.The proposed project aims at the development of a unified and seamless, i.e. a coherent turbulence and convection parameterization scheme. To solve this problem, we propose an approach that combines eddy diffusivity (K-approach) terms for local turbulence and mass flux terms for a variety of convective plumes for nonlocal turbulence and convection. As an intuitive formalism we will apply the transilient matrix method, in which each matrix element quantifies the transport between a certain source and target layer.In our project, the classical mass flux term will be replaced by a form allowing for net mass transport. A central question will be, when and to which extent the turbulent / convective circulation is resolved on the grid scale. In other words, when and how much net mass transport is to be parameterized. Sorting local turbulence, nonlocal turbulence, shallow and deep convection by their spatial scales, it becomes clear that there may be a more or less smooth transition from no to full net mass transport depending on the grid size of the hosting model. Furtheron, the involved physical processes such as thermodynamics, cloud formation and precipitation have to be controlled by physical arguments rather than model grid dependent decisions. Depending on the grid size, net mass transport will seamlessly taken into account in the spatial regimes of nonlocalturbulence / shallow convection.Because globally high-resolved NWP models are (and still will be) computationally too expensive for operational application, NWP has to rely either on a model chain or a multi scale model with online nesting. For both types of operational NWP models a coherent and scale adaptive turbulence and convection scheme will avoid the artificial switching between different schemes depending on the expected spatial scale of the dynamics and the current grid scale.In the scope of the proposed project, we will use the ICON model of DWD as the development environment but keep the parameterization scheme in a generalized form for implementation in other NWP models as well.