A highly scalable Met Office NERC Cloud model

Large Eddy Simulation is a critical modelling tool for scien- tists investigating atmospheric flows, turbulence and cloud microphysics. Within the UK, the principal LES model used by the atmospheric research community is the Met Office Large Eddy Model (LEM). The LEM was originally devel- oped in the late 1980s using computational techniques and assumptions of the time, which means that the it does not scale beyond 512 cores. In this paper we present the Met Office NERC Cloud model, MONC, which is a re-write of the existing LEM. We discuss the software engineering and architectural decisions made in order to develop a flexible, extensible model which the community can easily customise for their own needs. The scalability of MONC is evaluated, along with numerous additional customisations made to fur- ther improve performance at large core counts. The result of this work is a model which delivers to the community signifi- cant new scientific modelling capability that takes advantage of the current and future generation HPC machine

Profiling Methodology and Performance Tuning of the Met Office Unified Model for Weather and Climate Simulations

Global weather and climate modelling is a compute-intensive task that is mission-critical to government departments concerned with meteorology and climate change. The dominant component of these models is a global atmosphere model. One such model, the Met Office Unified Model (MetUM), is widely used in both Europe and Australia for this purpose. This paper describes our experiences in developing an efficient profiling methodology and scalability analysis of the MetUM version 7.5 at both low scale and high scale atmosphere grid resolutions. Variability within the execution of the MetUM and variability of the run-time of identical jobs on a highly shared cluster are taken into account. The methodology uses a lightweight profiler internal to the MetUM which we have enhanced to have minimal overhead and enables accurate profiling with only a relatively modest usage of processor time. At high-scale resolution, the MetUM scaled to core counts of 2048, with load imbalance accounting a significant fraction the loss from ideal performance. Recent patches have removed two relatively small sources of inefficiency. Internal segment size parameters gave a modest performance improvement at low-scale resolution (such as are used in climate simulation); this however was not significant a higher scales. Near-square process grid configurations tended to give the best performance. Byte-swapping optimizations vastly improved I/O performance, which has in turn a large impact on performance in operational runs

ADVISE: Agricultural developmental visualisation interactive software environment

We present here a package, ADVISE, which acts as a communication interface between the client, typically a graphics device, and the server, a computing resource such as a vector supercomputer, a parallel computer or some network of machines. The approach taken is that the information system comprises three component parts, those of client, server and interface. The interface is an object of sufficient sophistication to permit the use and development of each of the client and server modules separately. Further, multiple distinct jobs may be run simultaneously for multiple clients

Crossing the chasm: how to develop weather and climate models for next generation computers?

Weather and climate models are complex pieces of software which include many individual components, each of which is evolving under pressure to exploit advances in computing to enhance some combination of a range of possible improvements (higher spatio-temporal resolution, increased fidelity in terms of resolved processes, more quantification of uncertainty, etc.). However, after many years of a relatively stable computing environment with little choice in processing architecture or programming paradigm (basically X86 processors using MPI for parallelism), the existing menu of processor choices includes significant diversity, and more is on the horizon. This computational diversity, coupled with ever increasing software complexity, leads to the very real possibility that weather and climate modelling will arrive at a chasm which will separate scientific aspiration from our ability to develop and/or rapidly adapt codes to the available hardware. In this paper we review the hardware and software trends which are leading us towards this chasm, before describing current progress in addressing some of the tools which we may be able to use to bridge the chasm. This brief introduction to current tools and plans is followed by a discussion outlining the scientific requirements for quality model codes which have satisfactory performance and portability, while simultaneously supporting productive scientific evolution. We assert that the existing method of incremental model improvements employing small steps which adjust to the changing hardware environment is likely to be inadequate for crossing the chasm between aspiration and hardware at a satisfactory pace, in part because institutions cannot have all the relevant expertise in house. Instead, we outline a methodology based on large community efforts in engineering and standardisation, which will depend on identifying a taxonomy of key activities – perhaps based on existing efforts to develop domain-specific languages, identify common patterns in weather and climate codes, and develop community approaches to commonly needed tools and libraries – and then collaboratively building up those key components. Such a collaborative approach will depend on institutions, projects, and individuals adopting new interdependencies and ways of working.This paper reports European research funded by the following FW7 and H2020 research and innovation projects: IS-ENES2 under grant agreement 312979; ESCAPE under grant agreement no. 671627; and ESIWACE under grant agreement 675191. The authors acknowledge useful conversations with and input from Venkatramani Balaji, Terry Davies, Peter Fox, Rich Loft, Nigel Wood, and Andy Brown and the input of other participants at the “Crossing the Chasm” meeting, in particular Jean-Claude Andre, Joachim Biercamp, Antonio Cofiño, Marie-Alice Foujols, Sylvie Joussaume, Grenville Lister, Alastair Mckinstry, Annette Osprey, Øyvind Seland, and Manuel Vega.Peer Reviewe