LFRic: Meeting the challenges of scalability and performance portability in Weather and Climate models

• Published in: Journal of parallel and distributed computing Vol. 132; pp. 383 - 396
• Main Authors: Adams, S.V., Ford, R.W., Hambley, M., Hobson, J.M., Kavčič, I., Maynard, C.M., Melvin, T., Müller, E.H., Mullerworth, S., Porter, A.R., Rezny, M., Shipway, B.J., Wong, R.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01-10-2019
• Subjects: Domain specific language; Exascale; Numerical weather prediction; Separation of concerns; Separation of concerns; Domain specific language; Exascale; Numerical weather prediction
• ISSN: 0743-7315; 1096-0848
• DOI: 10.1016/j.jpdc.2019.02.007

This paper describes LFRic: the new weather and climate modelling system being developed by the UK Met Office to replace the existing Unified Model in preparation for exascale computing in the 2020s. LFRic uses the GungHo dynamical core and runs on a semi-structured cubed-sphere mesh. The design of the supporting infrastructure follows object-oriented principles to facilitate modularity and the use of external libraries where possible. In particular, a ‘separation of concerns’ between the science code and parallel code is imposed to promote performance portability. An application called PSyclone, developed at the STFC Hartree centre, can generate the parallel code enabling deployment of a single source science code onto different machine architectures. This paper provides an overview of the scientific requirement, the design of the software infrastructure, and examples of PSyclone usage. Preliminary performance results show strong scaling and an indication that hybrid MPI/OpenMP performs better than pure MPI.
•A new dynamical core and software infrastructure for weather and climate modelling.•Mixed finite element formulation on an unstructured mesh facilitates scalability.•A separation of concerns between domain and computational science.•Use of a Domain Specific Language and automatic code parallelism.•Modular design facilitating use of community libraries and frameworks.•Utilises object-orientated functionality of Fortran 2003.