CALIOP retrieval of droplet effective radius accounting for cloud vertical homogeneity

Monitoring cloud droplet effective radius (re) is of great significance for studying aerosol-cloud interactions (ACI). Passive satellite retrieval, e.g., MODIS (Moderate Resolution Imaging Spectroradiometer), requires sunlight. This requirement prompted developing re retrieval using active sensors, e.g., CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization). Given the highest sensitivity of vertically homogeneous clouds to aerosols that feed to cloud base, here CALIOP profile measurements were used for the first time to quantify cloud vertical homogeneity and estimate cloud re during both day and night. Comparison using simultaneous Aqua-MODIS measurements demonstrates that CALIOP retrieval has the highest accuracy for vertically homogeneous clouds, with R-2 (MAE, RMSE) of 0.72 (1.75 mu m, 2.25 mu m), while the accuracy is lowest for non-homogeneous clouds, with R-2 (MAE, RMSE) of 0.60 (2.90 mu m, 3.70 mu m). The improved re retrieval in vertically homogeneous clouds provides a basis for possible breakthrough insights in ACI by CALIOP since re in such clouds reflects most directly aerosol effects on cloud properties. Global day-night maps of cloud vertical homogeneity and respective re are presented. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

Monitoring cloud droplet effective radius (re) using CALIOP shows highest accuracy for vertically homogeneous clouds, providing a basis for breakthrough insights in aerosol-cloud interactions (ACI). Global day-night maps of cloud vertical homogeneity and respective re are presented.