Aerosol Optical Depth Impact on Oceanic Warm Clouds in Three Regions

This study investigates the influence of aerosol optical depth (AOD) on warm cloud microphysics in three distinct regions: East Asia (EA), the Equatorial Atlantic Ocean (EqAO), and Peru (PR), using Cloud Frequency by Optical Depth Diagram (CFODD) analysis. Satellite data from Aqua/MODIS and CloudSat/CPR during the period 2006-2014 were utilized to compare cloud properties under low and high AOD conditions. In EA, high AOD levels are associated with enhanced radar reflectivity at smaller cloud droplet radius (CDR), particularly within the 12-15 μm range. This indicates an increased droplet numbers and greater reflectivity variability within the same CDR interval. The observed enhancement in radar reflectivity at the cloud base under high AOD suggests an intensified collision-coalescence processes, consistent with the Anti-Twomey effect. A similar, though weaker, pattern is observed over the EqAO, indicating a reduced aerosol impact. In contrast, the PR region, exhibits minimal AOD variability, leading to limited aerosol effect and relatively stable cloud structures. These regional differences highlight the importance of considering both Twomey and Anti-Twomey effects to improve the representation of aerosol–cloud interactions (ACI) representation in climate models.