The effect of physical and chemical aerosol properties on warm cloud droplet activation

TLDR

Atmospheric aerosols have a potentially large but poorly quantified impact on climate forcing, especially through uncertain indirect effects on cloud radiative properties. The study investigates how aerosol composition and properties influence warm‑cloud droplet activation and thus the indirect climate effect. The authors evaluate aerosol size, composition, mixing state, and derived properties using observational data, test process‑level descriptions for sensitivity and closure, and review their implementation in global models, offering guidance for future work. Abstract.

Abstract

Abstract. The effects of atmospheric aerosol on climate forcing may be very substantial but are quantified poorly at present; in particular, the effects of aerosols on cloud radiative properties, or the "indirect effects" are credited with the greatest range of uncertainty amongst the known causes of radiative forcing. This manuscript explores the effects that the composition and properties of atmospheric aerosol can have on the activation of droplets in warm clouds, so potentially influencing the magnitude of the indirect effect. The effects of size, composition, mixing state and various derived properties are assessed and a range of these properties provided by atmospheric measurements in a variety of locations is briefly reviewed. The suitability of a range of process-level descriptions to capture these aerosol effects is investigated by assessment of their sensitivities to uncertainties in aerosol properties and by their performance in closure studies. The treatment of these effects within global models is reviewed and suggestions for future investigations are made.