Marine Warm Cloud Fraction Decreases Monotonically With Rain Rate for Fixed Vertical and Horizontal Cloud Sizes. Issue 3 (7th February 2023)

• Record Type: Journal Article
• Authors: Liu, Jihu; Zhu, Yannian; Wang, Minghuai; Rosenfeld, Daniel; Cao, Yang
• Is Part Of: Geophysical research letters. Volume 50:Issue 3(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-07
• Subjects: cloud fraction -- precipitation -- cloud geometric width -- cloud geometric thickness; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL101680
• Languages: English
• ISSNs: 0094-8276

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. Plain Language Summary: Changes in the cloud fraction (CF) of marine low‐level clouds have a considerable impact on the radiation budget because they reflect solar radiation into space and greatly cool the planet. Past studies have shown that precipitation plays an important role in the transition between different CF regimes, but the relationship between CF and precipitation remains controversial. Here we combined cloud properties and precipitation measurements from A‐train satellites to separate precipitation effects on CF from co‐varying factors. Our results show that both CF and rain rate ( R ) have a positive correlation with cloud geometric width (CGW) and thickness (CGT). R increases with CGW up to an optimum of 15 km for a fixed CGT, which may be because of less mixing of cloud water. However, as CGW grows above a critical size near 15 km, the cloud changes from convective to stratiform with less updraft and consequently less R . When CGT and CGW are both constrained, CF generally reduces monotonically as R increases. These findings point to the need to account for cloud morphology in cloud processes. Key Points: Both Cloud fraction and rain rate increase with cloud geometric width and thickness For a given cloud geometrical depth, rain rate increases with cloud geometric width up to an optimum near 15 km Cloud fraction generally decreases monotonically with increasing rain rate for fixed cloud horizontal and vertical sizes