On the Relation among Satellite Observed Liquid Water Path, Cloud Droplet Number Concentration and Cloud Base Rain Rate and Its Implication to the Auto-Conversion Parameterization in Stratocumulus Clouds

Abstract

AbstractPrecipitation processes play a critical role in the longevity and spatial distribution of stratocumulus clouds through their interaction with the vertical profiles of humidity and temperature within the atmospheric boundary layer. One of the difficulties in understanding these processes is the limited amount of observational data. In this study, robust relations among liquid water path (LWP), cloud droplet number concentration (Nd) and cloud base rain rate (Rcb) from three subtropical stratocumulus decks are obtained from A-Train satellite observations in order to obtain a broad perspective on warm rain processes.Rcbhas a positive correlation withLWP/Ndand the increase ofRcbbecomes larger asLWP/Ndincreases. However, the increase ofRcbwith respect toLWP/Ndbecomes more gradual in regions with largerNd, which indicates the relation is moderated byNd. These results are consistent with our theoretical understanding of warm rain processes and suggest that satellite observations are capable of elucidating the average manner of how precipitation processes are modulated byLWPandNd. The sensitivity of the auto-conversion rate toNdis investigated by examining pixels with smallLWPin which the accretion process is assumed to have little influence onRcb. The upper limit of the dependency of auto-conversion rate onNdis assessed from the relation betweenRcbandNd, since the sensitivity is exaggerated by the accretion process, and was found to be a cloud droplet number concentration to the power of −1.44 ± 0.12.