Global 2.8 km coupled simulations with the Integrated Forecasting System

Global kilometre‑scale modelling is advancing rapidly, supported by international efforts such as the 2025 global km‑scale hackathon (HK25) and the development of km-scale models in the nextGEMS, EERIE, and Destination Earth projects. As part of HK25, ECMWF produced two dedicated global coupled IFS–FESOM simulations and one atmosphere-only IFS (AMIP) simulation, representing one of the highest‑resolution global datasets currently available. Here we present the simulation setups, describe the creation of cloud and analysis-ready datasets, and showcase some initial results.

The simulations employ a fully coupled atmosphere–ocean–sea‑ice system at 2.8 km atmospheric resolution and around 5km in the ocean, explicitly resolving mesoscale ocean eddies, tropical cyclone cold wakes, and fine‑scale sea‑ice structures. The two coupled simulations differ only in their representation of atmospheric deep convection. Cloud‑ready Zarr output on the HEALPix grid enabled efficient analysis and remote access from the different HK25 nodes word-wide, and supported a number of case studies.

These 2.8 km simulations will form a core contribution to the DYAMOND3 intercomparison, providing some of the first fully coupled global simulations at this scale for coordinated intercomparison. Beyond this, the simulations enable unprecedented investigation of ocean–atmosphere interactions, including air–sea fluxes, mesoscale SST–atmosphere coupling, and the influence of ocean variability on extreme events.