Impacts of aerosols on MBL Cloud Microphysical and Drizzle Properties using Aircraft in-Situ Measurements during ACE-ENA

The relationships of marine stratocumulus microphysical properties, drizzle properties, and aerosol properties are examined using in-situ measurements obtained from the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA). During Summer 2017 and Winter 2018, 6 research flights and 5 research flights are selected as drizzling and non-drizzling cloud cases respectively, in order to investigate the cloud and drizzle susceptibilities to aerosol. The aerosol first indirect effect is well manifested in aircraft measurements. The cloud droplet number concentrations (N_d) show increasing trends with sub-cloud aerosol loading for both drizzle and non-drizzle cases. While the cloud droplet effective radius (r_e) decrease with increasing aerosol loading for non-drizzle cases. As for drizzle cases, r_e values show no significant dependence on the aerosol, which might due to the substantial impact of drizzle formation process on the droplet size distributions. It is noteworthy that there are different aerosol-cloud interactions near cloud-top and cloud-base regions, partly owing to the different air masses above (advected from polluted regions) and below (local source) the cloud layer. In terms of cloud drizzle susceptibility, relatively lower leg-mean cloud-base drizzle rates are found accompanied by relatively higher sub-cloud aerosol number concentrations, indicating increasing aerosol loading does effectively reduce drizzle production. Under given liquid water content condition, the drizzle susceptibility of Winter cloud cases is slightly higher than Summer cloud cases, suggesting the meteorological factors and aerosol sources might be jointly contributing to the aerosol suppression effect on drizzle.