Porting and enabling use of the Community Earth System Model on ARCHER

Key Personnel

PI/Co-I: Dr Massimo Bollasina and Dr Mike Mineter - The University of Edinburgh

Technical: Dr Gavin Pringle - EPCC, The University of Edinburgh

Relevant Documents

eCSE White Paper: Porting and Enabling Use of the Community Earth System Model on ARCHER

Project summary

The Community Earth System Model (CESM) is a coupled climate model for simulating the earth's climate system. Composed of four separate sub-models simultaneously simulating the earth's atmosphere, ocean, land surface and sea-ice, and one central coupler component, CESM allows researchers to conduct fundamental research into the earth's past, present and future climate states.

This project involved the porting to ARCHER and optimisation of two versions of CESM: the most current version (v1.2.2), and an older yet still popular version (v1.0.6). These are now both readily usable by the UK climate research community. The associated "amwg" tool was also made available.

Further, a methodology has been established for all UK researchers to work with the code on ARCHER via a new section on the ARCHER website.

Now that CESM is available, there will be a further growth in interest in the model. This state-of-the-art model complements those already planned for deployment on ARCHER, namely the Met. Office's Unified Model, WRF and WRF-CHEM, in that:

1. CESM simulates tropical climate better than current alternative models;
2. CESM is a prominent model developed by the US climate research community. There is the need to facilitate the comparison between US and UK state-of-the-art models in order to resolve uncertainties in climate projections;
3. CESM can exploit the high level of parallelism provided by ARCHER;
4. CESM can be configured in many ways, opening a wide range of avenues for climate research.

It should be noted that the climate research community views a model not so much as a black box to be invoked and run, but rather as a toolbox: an extensible, modifiable suite of software in which the code can be changed by the researcher to include different representations of physical processes.

This project has opened advantage to a research community that is wider than our own collaborations across three research groups, and includes the developers of the new UKESM model, which will need to be validated against other models.

An ARCHER-specific Validation Suite has been developed, based closely on CESM's own Validation Suite, which ensures that CESM is installed correctly; and two very large global climate simulations were employed to ensure CESM is installed efficiently. By switching from the default installation of serial I/O and low optimisation to using parallel I/O via pnetcdf, with careful striping, and higher optimisation, we have improved the out-of-the-box performance by just under 10%.

Summary of the software

The Community Earth System Model (CESM) is a coupled climate model for simulating the earth's climate system. Composed of four separate sub-models simultaneously simulating the earth's atmosphere, ocean, land surface and sea-ice, and one central coupler component, CESM allows researchers to conduct fundamental research into the earth's past, present and future climate states.

Both versions 1.0.6 and 1.2.2 have been ported and optimised for ARCHER, and detailed instructions may be found via http://www.archer.ac.uk/documentation/software/cesm/.

Users must first register with CESM to download CESM to their local disk and install CESM for their particular simulation(s). The CESM download page may be found at https://www2.cesm.ucar.edu/models/current/. Lastly, ARCHER-specific instructions and a number of ARCHER-specific files are provided via the ARCHER CESM webpage at http://www.archer.ac.uk/documentation/software/cesm/.