Exploring impacts of absorbing aerosol layers on underlying stratocumulus clouds using large-eddy simulation with explicit aerosol-radiation interactions.

Biomass-burning aerosol layers overlaying stratocumulus clouds are frequent over the Southeast Atlantic during the southern African fire season (June-October). This scenario can trigger a rich set of aerosol-cloud-radiation interactions with climatic consequences that are still poorly quantified. Although satellites and in-situ measurements provide useful information on these situations, the covariance between aerosols and meteorology makes it difficult to disentangle any causal aerosol impacts on stratocumulus clouds, a problem that can be avoided when using models. In this work, we have incorporated aerosol-radiation interactions into the large-eddy simulation code MIMICAV5 to study how a biomass burning aerosol layer (composed of black carbon and organic carbon) affects an underlying stratocumulus cloud over the Southeast Atlantic. More specifically, we explore how the arrival time (time of the day during the simulation) of the absorbing aerosol layer cloud affects the underlying stratocumulus cloud properties. In addition, we explore the susceptibility of cloud droplet number concentration in the stratocumulus cloud to the absorbing aerosol number concentration above the cloud.