EERIE: Ocean Eddy-rich Kilometer-scale Climate Simulation with ICON: Control Simulation (Version 1)

Project: European Eddy RIch Earth System Models - This project, running from January 2023 to December 2026, will reveal and quantify the role of ocean mesoscale processes in shaping the climate trajectory over seasonal to centennial time scales. To this end EERIE will develop a new generation of Earth System Models (ESMs) that are capable of explicitly representing a crucially important, yet unexplored regime of the Earth system – the ocean mesoscale. Leveraging the latest advances in science and technology, EERIE will substantially improve the ability of such ESMs to faithfully represent the centennial-scale evolution of the global climate, especially its variability, extremes and how tipping points may unfold under the influence of the ocean mesoscale.

Model improvements include new dynamical cores, new components (particularly for sea ice), scale-aware parametrisations and the complementary use of Machine Learning (ML). The technological challenge associated with this ambition is very high. EERIE’s goal is to achieve a simulation speed of up to 5 simulated years per day and to make efficient use (reduction in power consumption by 50%) of the pre-exascale supercomputers now available in Europe. The technological solutions that are to be leveraged in EERIE are the use of reduced numerical precision, Graphic Processing Units (GPUs), ML and reduced Input/Output (I/O). Alongside model improvements, EERIE will develop innovative experimental simulation protocols that are suitable for the mesoscale, to be pioneered on behalf of the global climate modelling community, in preparation for the next Intergovernmental Panel on Climate Change (IPCC) cycle.

(Ref: https://eerie-project.eu/about/)
Summary: The EU project European Eddy RIch Earth System Models (EERIE) is developing a new generation of Earth System Models (ESMs) that explicitly resolve ocean mesoscale dynamics, an essential but still poorly explored part of the climate system. By using recent advances in computing and model design, EERIE aims to improve long-term climate simulations, including variability, extremes, and potential tipping points influenced by mesoscale ocean processes.

ICON in Sapphire configuration is one of these new models. Developed at the Max Planck Institute for Meteorology, ICON couples the atmosphere, land, ocean, and sea ice at kilometer-scale resolution. It resolves deep atmospheric convection and captures mesoscale to sub-mesoscale ocean eddies, with the option to refine the global ocean grid locally as a “computational telescope.”

The atmospheric component uses a nonhydrostatic icosahedral C grid with a hybrid sigma-z vertical coordinate and parameterizes only unresolved processes (radiation, microphysics, turbulence). The ocean component shares the same grid and solves the hydrostatic Boussinesq equations, using only a subset of parameterizations such as vertical mixing and velocity dissipation. Sea ice is included via FESIM dynamics and a simplified thermodynamic scheme. Ocean biogeochemistry is represented by HAMOCC6, simulating more than 20 tracers. The land component, JSBACH 4, provides surface fluxes and simplified hydrology with prescribed vegetation. All components are coupled through the YAC coupler (v2.4.2).

The main simulations were preceded by a 40-year spin-up period using 1950 CMIP6 forcing. From the spin-up’s final state, two parallel simulations were started: a 100-year control run and a historical run. The control run is used to identify and quantify model drift, ensuring that any long-term changes in the historical simulation could be attributed to variations in radiative forcing rather than internal drift.