Coupling the regional climate model ICON-CLM v2.6.6 into the Earth system model GCOAST-AHOI v2.0 using OASIS3-MCT v4.0

Abstract. Interactions and feedback between compartments of the Earth system can have a significant impact on local and regional climate and its changes due to global warming. These effects can be better represented by regional Earth system models (RESMs) than by traditional stand-alone atmosphere and ocean models. Here, we present the RESM GCOAST-AHOI version 2.0, which includes a new atmospheric component, the regional climate model ICON-CLM, which is coupled with the ocean model NEMO and the hydrological discharge model HD via the OASIS3-MCT coupler. The GCOAST-AHOI model has been developed and applied for climate simulations over the EURO-CORDEX domain. Two 11-year simulations from 2008–2018 of the uncoupled ICON-CLM and GCOAST-AHOI give similar results for seasonal and annual means of near-surface air temperature, precipitation, mean sea level pressure and wind speed at 10 m height. However, GCOAST-AHOI has a cold SST bias of 1–2 degrees over the Baltic and the North Seas, most pronounced in winter and spring seasons. A possible reason for the cold SST bias could be the underestimation of the downward shortwave radiation at the surface of ICON with the current model settings. Despite of the cold SST bias, GCOAST-AHOI was able to capture other key variables such as those mentioned above well. Therefore, GCOAST-AHOI can be a useful tool to apply for long-term climate simulations over the EURO-CORDEX domain. The new OASIS3-MCT coupling interface OMCI implemented in the ICON-CLM model makes the ICON-CLM model more flexible to couple with an external ocean model and an external hydrological discharge model. Using OMCI, it is also possible to set up a RESM for other regions, such as the Mediterranean Sea.