Regionally focused aerosol-climate modelling at kilometer scale

Aerosol particles from natural and anthropogenic sources play an important role in the Earth's climate through their interactions with radiation and clouds. However, the underlying mechanisms and their climate impacts remain poorly understood. Kilometer-scale high-resolution climate simulations provide a powerful tool to tackle these uncertainties and reveal new details about the effects of aerosols, e.g., on moist convective clouds and fine-scale atmospheric dynamics. Recently, the reduced-complexity aerosol module HAM-lite was developed for global simulations within the ICON-MPIM Earth system model. While based on the proven but complex aerosol module HAM, HAM-lite represents aerosols as a group of logarithmic-normal modes with predefined sizes and compositions. It uses one mode each for pure dust and sea salt particles, and two internally mixed modes with organic carbon, black carbon, and sulfate. Now, this coupled model system has been further advanced to support limited-area mode (LAM) applications, enabling faster, targeted simulations of specific source and target regions and their associated aerosol processes.

We showcase the enhanced capability of ICON-MPIM and HAM-lite through LAM case studies. Regional simulations are performed at a resolution of approximately 2.5 kilometers over several months, using AMIP boundary conditions for sea surface temperature and sea ice. Initial and lateral boundary conditions for the atmosphere are sourced from ECMWF operational analysis, while aerosol boundary data are derived from either the Copernicus Atmosphere Monitoring Service reanalysis (EAC4 CAMS) or global ICON-MPIM-HAM-lite simulations. In this study, we present LAM applications for case studies of air pollution in Central Europe and Eastern Australia, densely populated regions with extensive aerosol measurement networks for model evaluation in the northern and southern hemispheres, respectively. Further analyses include aerosol processes at high-latitudes in the Fram Strait-Svalbard Arctic region, investigating the effects of sea ice on sea-spray emissions and polar air mass exchange; and low-latitude events in West Africa, focusing on the transport and impacts of dust and biomass burning smoke on regional climate and air quality.