Anthropogenic aerosol effects on convective clouds and precipitation in global km-scale simulations with ICON-HAM-lite 
Stier P., Weiss P., De S., Sela M., Jones W.
Aerosol effects on convective clouds and precipitation mediated via radiative and microphysical perturbations remain highly uncertain. Microphysical perturbations are generally not included in current climate models due to the simplified representation of convective clouds in existing parameterisations. Progress has been made through regional cloud resolving modelling; however, such simulations often neglect energy and water budget constraints and the coupling to larger scales. The emergence of global km-scale climate models provides a significant opportunity to advance our understanding of aerosol-convection interactions, but the inclusion of prognostic aerosols has been limited previously by their high computational demands.Here we present results from global km-scale atmospheric model simulations using ICON coupled to HAM-lite, a new reduced complexity aerosol model derived from the microphysical aerosol scheme HAM, suitable for global km-scale simulations [Weiss et al., GMD Discussions, 2024]. Performing aerosol perturbation experiments with pre-industrial and present-day aerosol emissions allows us to isolate anthropogenic aerosol effects on convective clouds and precipitation globally. As a first step, we compare simulated perturbations in terms of radiative (aerosol optical depth) and microphysical (cloud droplet number concentrations) against a set of observationally constrained idealised perturbations [Herbert et al., ACP Discussions, 2024]. This will allow us to put simulated cloud and precipitation responses in the simulations in the context of the perturbation strength.Comparison of our global km-scale simulations with prognostic aerosols with idealised simulations with prescribed aerosols [Herbert et al., 2024] provides a first insight into the effect of simulating global aerosols at the km-scale. Ultimately, this work offers a new way to study anthropogenic aerosol effects on convective clouds and precipitation globally, including microphysical and radiative perturbations, the diurnal cycle of convection, the coupling to the global circulation and regional climate.