Impact of aerosols on warm clouds over the Sichuan Basin, China in winter based on the MERRA-2 reanalysis dataset

Abstract

The impacts of aerosols on low warm clouds over the Sichuan Basin are still not well understood. We used the long-term Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) dataset to examine the relationships between aerosols and warm clouds in winter and explored the influence of meteorological conditions and different types of aerosols. There was a positive relationship between the aerosol optical depth and the cloud effective radius, cloud fraction and cloud optical thickness. However, the cloud top pressure tended to decrease with increasing aerosol optical depth. The influence of aerosols on warm clouds varied with the meteorological conditions. An analysis of the effects of thermal conditions, the vertical velocity and the relative humidity showed that stable atmospheric conditions, strong updrafts and a higher relative humidity increased the cloud fraction. Unstable atmospheric conditions and a high relative humidity also facilitated the formation of higher and thicker clouds. High sulfate aerosols were associated with moist air, a greater cloud fraction, a greater cloud optical thickness and a smaller cloud top pressure. Conversely, there was a smaller cloud fraction and cloud optical thickness and a greater cloud top pressure with drier air when there was a higher load of dust and black carbon aerosols.