Marine Warm Cloud Fraction Decreases Monotonically With Rain Rate for Fixed Vertical and Horizontal Cloud Sizes

Abstract

Abstract Precipitation has been hypothesized to play a key role in the determination of cloud fraction (CF). The relationships between CF and rain rate (R) in marine boundary layer clouds were studied based on long‐term satellite retrievals. We find that both CF and R increase with cloud geometric width (CGW) and thickness (CGT). Increased CGW causes increased R even without cloud deepening, but increasing CGW beyond 15 km leads to a slight decrease in R. Coincident change in CF and R with increased CGW causes a spurious positive CF‐R relationship. When fixing CGT and CGW, CF generally decreases monotonically with increasing R, and the dependence generally weakens with warmer sea surface temperature and thinner, larger clouds. This finding supports well the hypothesis that aerosols could increase cloudiness by suppressing precipitation. This study also emphasizes the importance of cloud morphology in marine boundary layer cloud studies connected to precipitation processes.

Keywords

• cloud fraction
• precipitation
• cloud geometric width
• cloud geometric thickness