Satellite observed aerosol-induced variability in warm cloud properties under different meteorological conditions over eastern China

Abstract

By taking meteorological conditions into account, this paper studies aerosol indirect effect on summertime warm clouds over the Yangtze River Delta (YRD) and East China Sea (ECS). The observed aerosol and cloud data are from MODIS/Aqua Level 2 datasets, and meteorological variables are from NCEP Final Analyses Operational Global Analysis datasets. To minimize meteorological effect on statistical analyses of aerosol-warm cloud interaction, several meteorological variables such as cloud top pressure (CTP), relative humidity (RH), pressure vertical velocity (PVV) and lower tropospheric stability (LTS) are considered in this study.Results show that cloud droplet radius (CDR) decreases with increasing aerosol optical depth (AOD) over ECS, while increases with increasing aerosol abundance over YRD. By taking CTP and RH into account, aerosol effects on cloud fraction (CF) are investigated. When aerosol loading is relatively small, CF is found to increase more sharply over YRD than over ECS in response to aerosol enhancement regardless of RH conditions. Therefore, we argue that the horizontal extension of cloud is prone to be driven by aerosol rather than meteorological conditions. Meanwhile, joint correlative analysis of AOD-CF and AOD-CTP reveals that CTP effect on AOD-CF is not significant, indicating CTP makes little contribution to observed AOD-CF relationship. Constrained by lower tropospheric stability (LTS) and pressure vertical velocity (750hPa), CDR variation in response to AOD is analyzed. In general, CDR tends to decrease as aerosol increases over both ECS and YRD under stable conditions (higher LTS value). In contrast, CDR positively responds to aerosol over land under unstable conditions. Dynamically, CDR has stronger effects on than the ascending motion than on the sinking motion with the same aerosol loading over both land and ocean. The reason can be partially explained by the phenomena that updrafts favor the growth of cloud droplets. Overall, the observed cloud variations can be extremely difficult to be attributed to aerosol particles alone due to dynamical and thermodynamical processes in cloud systems. © 2013 Elsevier Ltd.