Towards a Next generation Ocean Model in the Gung-Ho framework: 2D test cases (G-Ocean:2D)

该项目旨在开发和测试一种新的软件方法来编码海洋模型，这种方法可以利用下一代计算机架构。海洋模型是气候模型的一个重要组成部分，为政府间气候变化专门委员会（ipcc）等机构提供未来气候预测。它们也是探索从沿海到陆架海和全球尺度海洋环境各个方面的重要工具。海洋模型的使用依赖于世界上速度最快的国家计算机设备。计算机能力几乎每年都翻一番，随着这些设施的改进，海洋模型提供更精确模拟的潜力也在增加，这有利于气候和天气预报，以及我们对海洋环境的了解。然而，现在计算机能力的提高主要是通过提高并行性来实现的，每个芯片有更多的计算机内核，每台计算机有更多的芯片。因此，为了利用计算机能力的增长，我们必须开发能够利用尽可能多的不同形式的并行性的模型。虽然有很多方法可以实现这一目标，但它们通常是以牺牲模型开发的便便性为代价的，因此，最终只有计算机科学专家才能开发海洋模型——这是一个不合理的期望。海洋科学家希望利用计算机能力的提高的一种特殊方式是，在科学理解要求或对应用特别重要的地方，瞄准水平分辨率。为英国气象局（GungHo）开发一种新的大气模型的一个正在进行的项目已经确定了这些计算问题的解决方案，以应对这里所确定的许多相同的挑战和机遇。建议的解决方案是将模型计算机代码分成几层，每一层都需要不同的专业知识来开发，从而将自然科学家与计算机科学方面的复杂性隔离开来。虽然海洋和大气在物理上有许多相似之处，但也有一些重要的区别，特别是海洋深度的巨大变化和陆地的存在导致了复杂的边界，因为海洋不像大气那样覆盖整个地球。这自然导致海洋建模者在模型设计中不一定要做出与大气建模者相同的选择。因此，本项目的目的是将“分层方法”应用于一个简单的海洋案例，以证明以下概念：GungHo正在开发的计算框架足够灵活，可以适应海洋模型的网格和解决方法的自然选择。当在这个框架内编码时，传统的解决方案方法至少可以在效率和可扩展性方面与现有模型一样好，并且在高度优化时也具有易于使用和开发的好处。这项工作将提供在GungHo框架中构建和设计的海洋模型可能如何执行的第一个视图。这里建立的工具将允许我们探索海洋模型设计，并帮助回答这个问题：为GungHo开发的方法是否适合海洋？还是需要替代方案？这项工作的长期影响可能非常深远。我们的愿景是，这是迈向海洋模型的第一步，该模型可以在数十万到数百万个计算核心上高效运行，并且可以根据科学或用户兴趣的要求灵活地改变分辨率，同时也很容易被许多学科的海洋学家使用。实现这一愿景将代表地球系统建模和区域系统建模能力的一个步骤变化，这将是真正的世界领先。

This project aims to develop and test a new a software approach to coding ocean models that can exploit the next generation of computer architectures. Ocean models form a vital component of the climate models that produce future climate projections, for example, for the Inter-Governmental Panel on Climate Change. They are also important tools for exploring all aspects of the marine environment from coastal to shelf sea and global scales. The use of ocean models relies on national computer facilities that are among the fastest computers in the world. Computer power tends to approximately double every year, and as these facilities improve then so does the potential for ocean models to provide more accurate simulations, with benefits for climate and weather forecasting, as well as our understanding of the marine environment. However, increases in computer power are now occurring primarily through increased parallelism, with more computer cores per chip and more chips per computer. Hence to exploit increases in computer power we must develop models that can exploit as many different forms of parallelism as possible. While there are many ways of achieving this, they are generally at the expense of the ease of the development of the model, so that in time only a computer science expert would be able to develop the ocean model - an unreasonable expectation. One of the particular ways ocean scientists would want to use this increase in computer power is to target horizontal resolution where the scientific understanding dictates or where it is particularly important for the application.A solution to these computational issues has been identified in an on-going project to develop a new atmospheric model for the UK Met Office (GungHo) to meet many of the same challenges and opportunities identified here. The proposed solution is to separate the model computer code into layers, each requiring different expertise to develop, and so isolate the natural scientist from the complexities of the computer science aspects. While oceans and the atmosphere show many similarities in their physics, there are some important differences, notably the large changes in depth of the ocean and the presence of land leading to complex boundaries since the oceans do not cover the whole globe as the atmosphere does. This naturally leads to ocean modellers not necessarily making the same choices in model design as atmospheric modellers. Hence, the aim of this project is to apply the 'layered approach' to a simple ocean case to prove the concepts:1. That the computational framework under development in GungHo is sufficiently flexible to accommodate the natural choices of grids and solution approaches for ocean models.2. That, when coded within this framework, conventional solution approaches can perform at least as well as the existing models in terms of their efficiency and scalability, and also have benefits of ease of use and development when highly optimisedThis work will provide a first view of how an ocean model built and designed in the GungHo framework is likely to perform. The tools built here will allow us to explore ocean model design and help answer the question: Are the approaches being developed for GungHo appropriate for the ocean? Or will alternatives be needed? The long term impact of this work is potentially very far reaching. The vision is that this is the first step on the route to an ocean model that runs efficiently on hundreds of thousands to millions of computational cores and has flexibility to change resolution as the science or user interest dictates, but is also readily usable by oceanographers of many disciplines. Realising this vision would represent a step change in Earth System Modelling and Regional System Modelling capability that would be truly world leading.