Analyzing the Underestimation of Low Clouds in Satellite Observations Over the Southern Ocean
Anik Das1, Xiquan Dong1, Baike Xi1
1Department of Hydrology and Atmospheric Sciences
The University of Arizona, Tucson, AZ
The Southern Ocean (SO) serves as a natural laboratory for studying cloud formation and cloud-aerosol interactions with minimal anthropogenic influence. Dominated by low-level marine stratocumulus with significant supercooled liquid water, these clouds regulate the surface energy balance by reflecting solar radiation. The NASA CloudSat satellite, equipped with the 94 GHz Cloud Profiling Radar (CPR), has advanced global cloud observations, aiding passive satellite validation and climate modeling. However, CPR struggles with surface clutter, attenuation, and reduced sensitivity, particularly for marine boundary layer (MBL) clouds. Its 500-m pulse length limits detection below 500 m, while attenuation in high liquid water content clouds and a -26 dBZ sensitivity threshold contribute to underestimated cloud fractions (CF). To evaluate CPR’s MBL cloud detection, we compare cloud radar observations with two field campaigns: the aircraft-based SOCRATES (94 GHz HIAPER cloud radar) and the ship-based MARCUS (95 GHz M-WACR). These campaigns provided in-situ and remote sensing measurements of low-level SO clouds that CPR struggles to resolve. While all three radars detect large drizzle drops, M-WACR and HCR excel at detecting smaller cloud droplets missed by CPR. Underestimated CFs result from increased attenuation below 3 km and surface clutter below 1 km. Combining radar and lidar observations improved cloud detection by 20–60%. These findings provide insights for future cloud radar system designs, enhancing MBL cloud observations.