'Next Generation' unstructured mesh ocean global circulation modelling.

我们将建立比现有模式更精确、分辨率更高的下一代海洋全球环流模式。该模型将能够同时在全球、流域、区域和过程尺度上解决流动问题。它将能够改变数值细节，以响应建模流的结构和用户定义的特定重要区域和结构的偏好。我们将利用该模型进行现有模型无法进行的海洋研究。尽管在过去十年中取得了重大进展，但数值海洋全球环流模式（ogcm）基本上是基于与20世纪60年代开发的最早海洋模式相同的有限差分方法。与此同时，非结构有限元/体积方法已经在工程应用中得到了很大的应用，并为海洋建模提供了几个主要优势。这些能力包括：准确符合复杂的盆地几何形状；重点解决最需要的问题，以应对不断变化的流量或区域重要性；根据误差规范移动网格，保持垂直密度结构；以直接的方式纳入各种自然边界条件；并对模型误差和数值收敛性做出严格的表述。一个非结构化的网格海洋模型能够平滑和动态地改变分辨率，以响应不断变化的海洋动力学，可以被视为“网格嵌套的终极”，但避免了在巢边界匹配不同动态制度所固有的各种困难。尽管非结构化网格建模一直是许多海洋学家的目标，但由于在非结构化网格上准确稳定地处理科里奥利和浮力项的挑战，将这种方法应用于全球环流建模的尝试失败了。在过去的几年里，这个问题的重要解决方案已经被开发出来（其中许多是由我们开发的），并被纳入了帝国理工学院海洋模型（ICOM）。该模型具有最佳的并行网格自适应方法，一套空间导数选项（如密度/示踪平流的高分辨率方法），新颖而稳健的平衡处理，优化的测深和海岸线几何形状以及新的大涡网格自适应湍流模型。国际博协将成为拟议财团建立的OGCM的基础。它的驱动因素有两个：(a)一个新的研究工具是必要的，因为“标准”有限差分代码变得更难调整以提高其准确性；(b)存在重大的科学问题，其中长度尺度之间的差异需要应用新的建模技术，例如我们的技术（例如流过斜坡和斜坡的流动，涡流，环流内的对流等）。这些方法有可能彻底改变海洋建模的方式，从而确保英国海洋建模在该领域的前沿的长期未来。下一代海洋模型具有有效解决大范围尺度的能力，将在NERC和更广泛的社区中有许多应用。对于海洋建模者来说，它提供了有效解决盆地尺度环流和小尺度过程的机会，如边界流、过流和溢流以及地转涡旋。对于地球系统和气候建模者来说，它提供了将分辨率集中在特别重要的区域的机会，例如边界流和溢出，而不会比传统的粗分辨率模型增加计算成本。在海洋学、气候变化、防洪、污染和污染物扩散、水质可持续性和渔业等领域有着广泛的应用，开发这样的模型是非常可取的。

We will build a next generation ocean global circulation model that is more accurate and has more detailed resolution than existing models. This model will be capable of resolving flows simultaneously on global, basin, regional, and process scales. It will be able to change numerical detail in response to both the structure of the modelled flows and user-defined preferences of regions and structures of specific importance. We shall use the model to carry out ocean research which is not possible with existing models. Despite significant advances over the past decade, numerical ocean global circulation models (OGCMs) are based on essentially the same finite-difference methods employed in the earliest ocean models developed in the 1 960s. Meanwhile, unstructured finite element/volume methods have been deployed to great effect in engineering applications and offer several major advantages for ocean modelling. These include the abilities to: conform accurately to complex basin geometries; focus resolution where it is most needed in response to the evolving flow or regional importance; move the mesh in response to error norms and maintain vertical density structures; incorporate various natural boundary conditions in a straightforward manner; and to make rigorous statements about model errors and numerical convergence. The ability of an unstructured mesh ocean model to change resolution smoothly and dynamically in response to changing ocean dynamics can be viewed as the 'ultimate in grid nesting', but avoiding the various difficulties inherent in matching different dynamical regimes at nest boundaries. Although unstructured mesh modelling has long been a goal of many oceanographers, attempts to apply such methods to model the global circulation have failed due to challenges in treating the Coriolis and buoyancy terms accurately and stably on unstructured meshes. Over the past few years important solutions to this problem have been developed (many by us) and incorporated into the Imperial College Ocean Model (ICOM). This model has the best available parallel mesh adaptivity methods, a suite of options for spatial derivatives (such as high-resolution methods for density/tracer advection), novel and robust treatments of balance, optimised bathymetry and coastline geometries and new large eddy mesh adaptive turbulence models. ICOM will form the foundation of the OGCM built by the proposed consortium. The drivers for it are twofold: (a) a new research tool is a necessity as 'standard' finite-difference codes become harder to tweak to improve their accuracy; and (b) there are significant science problems where the disparity between length scales requires the application of new modelling techniques such as ours (e.g. flow through sills and down slopes, eddies, convection within gyres, etc). These methods have the potential to revolutionise the way in which ocean modelling is done, and thus to secure the long-term future of UK Ocean Modelling at the forefront of the field. The next generation ocean model, with its ability to efficiently resolve a wide range of scales, will have numerous applications to the NERC and wider communities. For ocean modellers, it offers the opportunity to efficiently resolve both basin scale circulation and small-scale processes such as boundary currents, through- and overflows and geostrophic eddies. For Earth system and climate modellers, it offers the opportunity to focus resolution in regions of particular importance, such as boundary currents and overflows, without increasing the computational cost above that of a conventional coarse-resolution model. With a wide range of applications in oceanography, climate change, flood defence, pollution and contaminant dispersal, sustainability of water quality and fisheries, the development of such a model is extremely desirable.