Profiles of MBL Cloud and Drizzle Microphysical Properties Retrieved From Ground-Based Observations and Validated by Aircraft In Situ Measurements Over the Azores

The profiles of marine boundary layer (MBL) cloud and drizzle microphysical properties are important for studying the cloud-to-rain conversion and growth processes in MBL clouds. However, it is challenging to simultaneously retrieve both cloud and drizzle microphysical properties within an MBL cloud layer using ground-based observations. In this study, methods were developed to first decompose drizzle and cloud reflectivity in MBL clouds from Atmospheric Radiation Measurement cloud radar reflectivity measurements and then simultaneously retrieve cloud and drizzle microphysical properties during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign. These retrieved microphysical properties, such as cloud and drizzle particle size (r_c and r_m,d), their number concentration (N_c and N_d) and liquid water content (LWC_c and LWC_d), have been validated by aircraft in situ measurements during ACE-ENA (~158 hr of aircraft data). The mean surface retrieved (in situ measured) r_c, N_c, and LWC_c are 10.9 μm (11.8 μm), 70 cm⁻³ (60 cm⁻³), and 0.21 g m⁻³ (0.22 g m⁻³), respectively. For drizzle microphysical properties, the retrieved (in situ measured) r_d, N_d, and LWC_d are 44.9 μm (45.1 μm), 0.07 cm⁻³ (0.08 cm⁻³), and 0.052 g m⁻³ (0.066 g m⁻³), respectively. Treating the aircraft in situ measurements as truth, the estimated median retrieval errors are ~15% for r_c, ~35% for N_c, ~30% for LWC_c and r_d, and ~50% for N_d and LWC_d. The findings from this study will provide insightful information for improving our understanding of warm rain processes, as well as for improving model simulations. More studies are required over other climatic regions.