ARCHER2 eCSE project: Porting, testing, optimising, and configuring the Community Earth System Model

The Community Earth System Model 2 (CESM2) is a world-leading global climate model developed by the National Center for Atmospheric Research (NCAR) in the USA. NCAR provides not only the CESM2 code and support but also various experiments and output for two main purposes: to provide climate projections and predictions, and to make it usable as a state-of-the-art research tool. CESM2 is widely recognized and successfully used by the international research community. The availability of CESM2 to the UK research community opens up a wide range of avenues for various research directions, collaborations, and applications.

This project aimed at porting, optimising, testing, and validating the model’s key configurations and making them available to the UK community through ARCHER2, the UK National Supercomputing Service. A quick start guide, as well as the codes involved and documentation to set up experiments, have been now made available through the ARCHER2 website.

CESM2 is a fully-coupled, community, global climate model that provides state-of-the-art computer simulations of the Earth's past, present, and future climate states. This level of complexity requires careful documentation that is best tested by someone who is HPC literate but external to the CESM2 development team.

The main part of this testing focussed on the four CESM2 benchmarks, checking that these would run as expected for someone unfamilliar with the CESM2 climate model. Several simulation types are covered by the benchmarks, atmosphere-only, slab-ocean and coupled (atmosphere+ocean). Small 4-8 node jobs were run for long enough to capture a meaningful performance metric, eg simulation years per day (SYPD).

Issues discovered were incorrect paths to input data, incompatible software modules and insufficient workload distribution for the coupled benchmarks. The latter was rectified by altering the mesh resolution. The other two problems were caused by attempting to run the benchmark outside of the n02 NERC consortium project. The documentation was altered to make it clear that users must run the CESM2 instructions from within the n02 project on ARCHER2. 

Find out more

Read the full report on the ARCHER2 website: Porting, Testing, Optimising, and Configuring the Community Earth System Model (CESM2) on ARCHER2

ARCHER2, the UK’s National High Performance Computing system