D2.4: Report documenting Task Readiness Review
Creators: name: Becker, Tobias
name: Pedruzo-Bagazgoitia, Xabier
name: Klocke, Daniel
name: Rackow, Thomas
name: Sandu, Irina
Publisher: name: Zenodo
Year: 2023

description: About this document

This report will describe the improvements to SR-ESMs in Cycles 1 and 2 (including output, and workflows) and will assess readiness for the final preparations for the production simulations.

Work package in charge

WP2

Executive summary

The purpose of this report is to summarise the readiness of the SR-ESMs for performing the Cycle 3 nextGEMS simulations, in advance of final preparation for the production simulations. We summarise both the changes made so far for improving ICON and IFS-FESOM/NEMO, and the remaining challenges that are currently being tackled. We also highlight the experiences in organizing and implementing community input through Hackathons, and how this contributed to develop the SR-ESMs and to ensure their usability for the applications. 

The report shows that the two storm-resolving Earth System Models (SR-ESM), ICON and IFSFESOM/NEMO, will be ready for the next cycle of nextGEMS, Cycle 3, within the next few weeks. This concerns both technical readiness as well as climate-readiness. Both SR-ESMs are also in a good position for the production runs that will be started by the end of 2023. 

Conclusion & Results

With respect to model climate-readiness, the ICON and IFS-FESOM/NEMO configurations have seen great progress with respect to fixing energy and water imbalances, as summarised below.

For ICON, a major hurdle for long climate integrations has been the large net energy flux imbalance at the top of the atmosphere (-5 W m−2). This imbalance was caused by an energy leak in the atmosphere component of the model; in particular, the leaks were identified in the microphysics, and in the turbulence and dynamics schemes of the model. To address these issues, the micro-physics and turbulence schemes were rewritten. Other updates were added for the land (new land maps based on high resolution observations) and the ocean (new vertical coordinate in the ocean to allow for thin layers at the model top). The hydrological discharge from land to ocean now also works with thin ocean layers in high resolution configurations.

In preparation for multi-year coupled simulations with the IFS, the atmospheric water and energy imbalances as well as the top-of-atmosphere imbalances of longwave and shortwave radiation have been strongly reduced, keeping all imbalances below 1 W m−2. This will reduce the drift in global-mean 2m temperature to a minimum in the Cycle 3 simulations. In addition, the representation of several processes that are important for the climate system (atmosphere, land and ocean) have become more realistic. The key model updates include: (i) reduced cloud base mass flux in the convection scheme, (ii) introduction of a new multi-layer snow scheme, and (iii) new high-resolution ocean grid, NG5, which is used in FESOM.

With respect to technical readiness, ICON has demonstrated that the necessary functionality for multi-year integrations is there. Further progress has been made with the atmospheric component of ICON in making effective use of GPUs on several compute systems. The ocean component is still relying on CPUs, but the model can be used in a hybrid configuration as well, where the atmosphere runs on a GPU cluster and the ocean on the CPU cluster of the same compute centre.

For the IFS, technical developments were centered around using the ”Real Applications on Parallel Systems” portable environment (short RAPS) in different supercomputer environments; and around extending IFS capabilities for performing multi-year simulations. Another stream of development dealt with optimising data workflows and model performance by writing simulation output with the forecast database software (FDB), as well as with multIO postprocessing pipelines.