Zhanqing Li^1,2,3, Feng Niu³, Jiwen Fan⁴, Yangang Liu⁵, Daniel Rosenfeld⁶ and Yanni Ding³

¹ State Key Laboratory of Earth Surface Processes and Resource Ecology, GCESS, Beijing Normal University, Beijing 100875, China.

² College of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China.

³ Department of Atmospheric and Oceanic Science & ESSIC, University of Maryland, College Park, Maryland 20742, USA.

⁴ Atmospheric Science and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.

⁵ Atmospheric Sciences Division, Brookhaven National Laboratory, Upton, New York 11973, USA.

⁶ Institute of Earth Sciences, The Hebrew University of Jerusalem, Jerusalem 91904, Israel.

 

Abstract: Aerosols alter cloud density and the radiative balance of the atmosphere. This leads to changes in cloud microphysics and atmospheric stability, which can either suppress or foster the development of clouds and precipitation. The net effect is largely unknown, but depends on meteorological conditions and aerosol properties. Here, we examine the long-term impact of aerosols on the vertical development of clouds and rainfall frequencies, using a 10-year dataset of aerosol, cloud and meteorological variables collected in the Southern Great Plains in the United States. We show that cloud-top height and thickness increase with aerosol concentration measured near the ground in mixed-phase clouds—which contain both liquid water and ice—that have a warm, low base. We attribute the effect, which is most significant in summer, to an aerosol-induced invigoration of upward winds. In contrast, we find no change in cloud-top height and precipitation with aerosol concentration in clouds with no ice or cool bases. We further show that precipitation frequency and rain rate are altered by aerosols. Rain increases with aerosol concentration in deep clouds that have a high liquid-water content, but declines in clouds that have a low liquid-water content. Simulations using a cloud-resolving model confirm these observations. Our findings provide unprecedented insights of the long-term net impacts of aerosols on clouds and precipitation.