The main components of an atmospheric model for numerical weather prediction are the dynamical core, which describes the resolved flow, and the physical parametrisations, which capture the effects of unresolved processes. Additionally, models used for air quality or climate applications may include a component that represents the evolution of chemicals and aerosols within the atmosphere. While traditionally all these components use the same mesh with the same resolution, we present a formulation for the different components to use a series of nested meshes, with different horizontal resolutions. This gives the model greater flexibility in the allocation of computational resources, so that resolution can be targeted to those parts which provide the greatest benefits in accuracy. The formulation presented here concerns the methods for mapping fields between meshes, and is designed for the compatible finite element discretisation used by LFRic-Atmosphere, the Met Office's next-generation atmosphere model. Key properties of the formulation include the consistent and conservative transport of tracers on a mesh that is coarser than the dynamical core, and the handling of moisture to ensure mass conservation without generation of unphysical negative values. Having presented the formulation, it is then demonstrated through a series of idealised test cases which show the feasibility of this approach.

翻译：数值天气预报大气模型的主要组成部分是描述解析流动的动力学核心和捕捉未解析过程影响的物理参数化。此外，用于空气质量或气候应用的模型可能包含代表大气中化学物质及气溶胶演化过程的组分。传统上，所有这些组件均使用相同分辨率的同一网格。然而，我们提出了一种新方案，允许不同组件使用一系列嵌套网格并具有不同的水平分辨率。这赋予模型更大的计算资源分配灵活性，从而可将分辨率集中于能最大程度提升精度的区域。本文提出的公式涉及网格间场映射方法，专为英国气象局下一代大气模型LFRic-Atmosphere采用的兼容有限元离散化设计。该公式的关键特性包括：在比动力学核心更粗糙的网格上实现示踪物的一致守恒输运，以及处理水汽以确保质量守恒且不产生非物理负值。在阐明公式后，我们通过一系列理想化测试案例验证了该方法的可行性。