Impact of the online climate-chemistry in regional climate simulations in meteorological variables over Europe

Work Package 4 of the FOCI project (“Non-CO2 Forcers and their Climate, Weather, Air Quality and Health Impacts”; https://www.project-foci.eu/wp/) is tasked with tuning, testing, and conducting long-term simulations to validate various regional models in downscaling of reanalysis and global climate models for historical period. The long-term simulations are performed by RegCM5-Chem and WRF-Chem, both of which are coupled with chemistry over the European domain. A notable aspect of this work is the use of RegCM5-Chem for long-term simulations, which is a novel approach within the community. Besides that, the land cover is dynamic, derived from the Land Use and Climate Across Scales flagship pilot study of the EURO-CORDEX initiative. The initial and boundary conditions for the atmospheric variables and chemical composition were created from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis version 5 (ERA5) and Atmospheric Composition Reanalysis 4 (EAC4) datasets. Emissions of atmospheric pollutants and greenhouse gases are obtained from the Copernicus Atmosphere Monitoring Service (CAMS) high-resolution European emission inventory for air quality modeling. E-OBS is utilized for validating the outputs. Sensitivity tests have shown that coupled chemistry impacts surface meteorological variables, such as temperature and shortwave radiation. In this study, we will evaluate these variables in greater detail, as well as examine how this coupling affects precipitation and surface wind speed. It is important to note that the chemical mechanism enables interactive coupling between modeled ozone and its radiative effects, as well as between gas-phase chemical processes and aerosol formation. These interactions, in turn, have feedback on the radiative, thermodynamic, and dynamic fields. This evaluation is crucial for enabling further comparisons with simulations driven by EC-Earth-AerChem in both present and future climates, as part of FOCI Work Package 6.