Relative roles of aerosol size and hygroscopicity in modulating marine liquid-phase cloud responses under the winter monsoon

Abstract. How aerosol physicochemical properties affect aerosol-cloud interactions (ACI) and when these impacts are most pronounced represent an important source of ACI uncertainty. Targeting a representative liquid-phase cloud case over the Eastern China Ocean (ECO) under the winter monsoon featuring abundant meteorological, aerosol, and cloud variations, this study investigates the impacts of changes in aerosol size (volume-mean radius increased by 1.2 times and decreased by 45 %) and hygroscopicity (volume-mean hygroscopicity increased by 2.2 times and decreased by 62 %) using a spectral-bin cloud model. Results indicate that increased aerosol size and hygroscopicity generally enhance cloud development, raising the ECO-averaged cloud droplet number concentration (N_d) by 92 % and 53 %, respectively. These impacts peak under moderate aerosol concentrations (N_a) and cold advection, where N_d increases up to 10-fold. Concurrently, increased aerosol size raises cloud water by 1.3 times and extends cloud lifetime by 85 %, whereas increased hygroscopicity has a much weaker effect. By contrast, decreased aerosol size and hygroscopicity generally suppress cloud development, reducing the ECO-averaged N_d by 49 % and 43 %, respectively. The former has a relatively strong impact, which is most notable in moderate-to-high N_a environments under cold advection, reducing N_d and cloud water by over 80 % and 50 %, respectively. While changes in aerosol size generally exert a stronger overall impact than changes in hygroscopicity, specific conditions reveal the opposite. Notably, the enhancement of N_d by increased hygroscopicity under high N_a, and the preservation of cloud and rainwater through evaporation suppression by decreased hygroscopicity, both surpass the effects caused by corresponding aerosol size changes.