Evaluating LES models across aerosol- and updraft-limited susceptibility regimes

Aerosols play an important role in cloud formation, radiative forcing and precipitation formation. However, the representation of aerosol-cloud interactions in climate models still causes one of the largest uncertainties in future climate projections. Large Eddy Simulation (LES) models have become useful tools for bridging our understanding of small-scale processes with parametrization development for Earth System Models (ESMs). Previous studies have exposed substantial inter-model variability in reproducing the susceptibility of cloud droplet number concentrations (CDNC) to cloud condensation nuclei (CCN) concentrations across aerosol- and updraft-limited regimes. Our work will ultimately contribute to the development of ESMs for reliable future projections under scenarios of changing aerosol emissions. We present preliminary results from the evaluation of LES model output against in-situ observations of aerosol and clouds microphysics and chemistry, from observation sites representing different ranges within the aerosol- and updraft-limited susceptibility regimes. To develop new process-based constraints for LES models, we will utilize data collected during the ARTofMELT expedition in the Arctic, the FAIRARI campaign in the Po Valley and the NOMODODO campaign at the Maïdo Observatory in La Réunion. The diverse settings of the observations give the chance of investigating case studies with varying aerosol loadings and land-atmosphere interactions. As we are interested in cloud susceptibility regimes and aerosol indirect effects on clouds, we mainly focus on liquid-phase processes. We analyze liquid water content, CDNC, CCN concentrations, and aerosol chemical composition. We also examine the shape of the aerosol and cloud droplet size distributions. This study serves as a benchmark to build more consistent representations of aerosol-cloud interactions in numerical models. Our results will be used to inform further research on the sensitivity of cloud properties to aerosol and cloud microphysical processes.