The Association Between Rain Rates in Shallow Subtropical Marine Clouds and Marine Atmospheric Boundary Layer Circulations Observed by Synthetic Aperture Radar

Abstract Extensive, coherent circulations in the marine atmospheric boundary layer (MABL) are detected and classified using an automated image processing routine applied to synthetic aperture radar (SAR) images from Sentinel‐1 over subtropical oceans at sunrise and sunset. Circulations are inferred from patterns of capillary waves detected by the SAR. Classifications include wind streaks (WS, the surface imprint of roll structures), microscale convective patches (MC), combined WS/MC, cold pools, and rain columns. Using 12‐hr Lagrangian trajectories, classified MABL states are linked to warm rain rates estimated from the Advanced Microwave Scanning Radiometer (AMSR/2) sensor and to cloud variables observed by the Moderate Resolution Imaging Spectroradiometer (MODIS) in NASA's A‐Train, to assess whether MABL states correspond to variations in rain rates, and other cloud variables, including cloud drop concentration, water content, and cloud top height. Results indicate that rain rates and cloud water path observed along trajectories that contain cold pools and rain columns, as seen by SAR, are greater than in other states. Wind streaks are associated with higher rain rates than MC and WS/MC, even after controlling for a selection of confounding variables, while cloud top heights are higher in MC environments. A sensitivity test shows that rain rates are significantly more sensitive to a selection of predictors when WS are present compared to MC.