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

Lead Research Organisation: STFC - Laboratories
Department Name: Scientific Computing Department

Abstract

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 two years, 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 corers 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 easy of the development of the model, until we might expected only a computer science expert to be able to develop the ocean model - an unreasonable expectation. One of the particular ways oceans scientists would want to use this increase in computer power is by targeting horizontal resolution where the scientific understanding dictates or where it is particularly important for the application.
A solution to the computational issue 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, they are some important differences, notably the large changes in depth for the ocean and present of land giving complex boundaries and also implying the oceans do not cover the whole globe as the atmosphere does. This naturally leads to ocean modellers not necessarily making the same choices, as in the atmospheric model. 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 Gung-Ho is sufficiently flexible to accommodate the natural choices of grids and solution approaches for ocean models
2. That, when coded within this framework, conventional modelling 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 optimised
This 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.

Planned Impact

The impact of this work lies in its effect on the evolution of ocean modelling in the UK and potentially in Europe and world wide. This proof of concept project is the first step towards the long term goal of being able to run ocean models, with an advanced multiscale capability, that effectively exploit the computational architectures that will be available in 5-10 years time, with a 50-1000 fold increase in computer power over current capability. The impacts of realising this goal would be substantial, benefiting all aspects of applied ocean modelling, on all scales from coastal to global ocean, via shelf seas and regional basins.
Potential, direct beneficiaries include government departments (e.g. DEFRA, DECC, DiFD, MOD), agencies (e.g. Met Office, CEFAS, Environment Agency), international programmes involved in climate change assessment, adaptation and mitigation measures (e.g. IPCC and Future Earth), and commercial users of environmental and climate information, (e.g. offshore mineral extraction, shipping, insurance, and fisheries industries.)
Commercialisation opportunities exist in the use of the model as a regional prediction system, to provide user tailored oceanographic products, particularly at a shelf to coastal scale.
Overall, the aim is that ocean models of the future will be run at a much higher resolution than at present, exploiting the massive increases in computer power which will become available. This is expected to give more accurate predictions through the more reliable inclusion of small-scale physical processes, bathymetry and coastlines. This will only be possible, though, if we are able to fully exploit the increased parallelism of those future computers. The present proposal represents the necessary first step towards this goal.
The primary mechanism for delivering impact from this work is through the Joint Weather and Climate Research Programme (JWCRP; the programme that oversees joint NERC and Met Office work). As this work evolves (beyond this project), it will be taken up through the JWCRP into the UK Earth System Model and GloSea seasonal forecasting system (through the Joint Ocean Modelling Programme), the UK Environmental Prediction System (through the Joint Coastal Ocean Modelling Programme), and into ocean forecasting through NCOF (the National Centre for Ocean Forecasting). The key players in these groups will be invited to the final project workshop, and discussion of the best way to take this forward will continue throughout the project.
Another important mechanism for delivering impact is through the NEMO steering and developer committees and this work will inform the on-going debate on how the international NEMO consortium should evolve in the long to medium term. CoI New is a member of the NEMO steering committee and PI Holt is an 'Invited expert' on the NEMO developers committee.
Once the barotropic (2D) solution of this model has been proved to give good results with realistic forcing and topography, there is an opportunity for early commercialisation of this work as a tidal prediction tool.

Publications

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Description We have shown for an ocean model kernel that the code related to the underlying science may be formally separated from code related to parallelisation and single core optimisations. This separation of concerns allows
scientists to code their science independently of the underlying hardware architecture (thereby keeping a single code base) and for optimisation specialists to be able
to tailor the code for a particular machine independently of the science code.
Exploitation Route The framework described in our work may be applied to many areas of computational science to improve portability while maintaining performance across a range of HPC architectires.
Sectors Aerospace, Defence and Marine,Chemicals,Energy,Environment,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology