Scalability on pre-exascale EuroHPC systems - Deliverable D1.3

The central objectives of Work Package 1 of ESiWACE2 is to develop and run coupled model simulations at a resolution as high as possible and with a throughput rate of at least one simulated year per day (1 SYPD) producing full model output. This throughput would be sufficient to use these simulations for operational weather predictions and potentially also to run the models for a couple of decades, to address scientific questions that are related to climate change. Four model configurations are considered: EC-Earth with OpenIFS coupled to NEMO, the Integrated Forecasting System (IFS) coupled to NEMO, the ICON model with both atmosphere and ocean, the DYNAMICO model coupled to NEMO, covering both weather and climate configurations as well as well-established models and models that are currently under development. Furthermore, ocean-only simulations with the NEMO models are also pushed to very high spatial resolution (1/36 ◦ ; ∼3 km).
According to the initial plan, the main aim of this deliverable was to perform scalability tests on the pre-exascale EuroHPC systems. However, this was impossible as these machines are only just becoming available. The deliverable is therefore focusing on the ongoing work to make the models more efficient and to enable the porting of the codes to heterogeneous hardware. As the European pre-exascale machines were not available, some tests of the models on other European HPC systems and some of the world’s fastest supercomputers (Summit and Fugaku) are also documented. Furthermore, the work on the treatment of output from ensemble simulations using XIOS that was moved from Deliverable D1.1 is also documented here, showing the successful use of XIOS to generate ensemble model output straight from ensemble simulations.