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

在数值天气预报（NWP）模式中，亚网格尺度的垂直运动通常采用湍流方案或对流方案。决定通常是基于浮力或剪切不稳定性导致的动力学的预期垂直范围：如果运动是短的垂直范围和/或局限于行星边界层（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。由于自然界中对湍流和对流的分类没有严格的限制，因此提出了统一或相干的湍流和对流参数化方案，本项目的目标是发展一个统一和无缝的，即相干的湍流和对流参数化方案。为了解决这个问题，我们提出了一种方法，结合涡扩散（K-方法）条款的局部湍流和质量通量条款的各种对流羽流的非局部湍流和对流。作为一种直观的形式主义，我们将应用瞬态矩阵方法，其中每个矩阵元素量化特定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替换为允许净质量传输的形式。一个中心问题是，何时以及在何种程度上的湍流/对流环流是解决网格尺度。换句话说，何时以及有多少净质量传输是参数化的。通过对局部湍流、非局部湍流、浅对流和深对流的空间尺度进行分类，可以清楚地看出，根据托管模型的网格大小，从没有到完全净质量输送可能会有一个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控制的物理参数，而不是模型网格依赖的决定。根据网格的大小，净质量输运将无缝地考虑到在nonlocalturbulence /浅对流的空间regimes.Because全球高分辨率NWP模式是（仍然会）计算太昂贵的业务应用，NWP必须依赖于一个模式链或多尺度模式与在线嵌套。对于这两种类型的业务NWP模式，相干和尺度自适应湍流和对流方案将避免根据动力学的预期空间尺度和当前网格尺度在不同方案之间进行人为切换。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模型中实现，好.

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.