Microphysics effects of anthropogenic aerosols on urban heavy precipitation over the Pearl River Delta, China

Abstract

In this study, the Weather Research and Forecasting model coupled with chemistry was used to simulate cloud microphysics processes of a mesoscale urban heavy precipitation event over the Pearl River Delta, China. Two intensities of anthropogenic emissions were considered: the E2010 simulation adopted the level and distribution of present-day pollution, while the E1960 simulation adopted the aerosol condition before urbanization. The modeling reproduced the precipitation process and the results showed a more centralized distribution of precipitation and a rain rate that was 20% higher at the mature stage in E2010. A larger area of convective-type precipitation occurred in E2010 (51.2%) than in E1960 (42.3%), but less stratiform- and mixed-type precipitation occurred in E2010 (7.6% and 7.3%, respectively) than in E1960 (12.1% and 9.1%, respectively). In comparison with E1960, E2010 produced larger quantities of cloud droplets and ice-phase particles. Additional release of condensation/deposition latent heating promoted vertical upward motion and convection in clouds, which further promoted the riming process between hail and raindrops/cloud droplets, as well as the colliding, merging, and collecting processes between raindrops and droplets that ultimately generated raindrops with larger radii (600–700 μm) but smaller number concentrations. Furthermore, hydrometeors convert to precipitation more effectively in polluted conditions. In E2010, the centralized distribution and greater mass magnitude of hail and melting hail resulted in a focused distribution of rainfall. In E1960, the decentralized distributions and smaller mass magnitude of hail and melting hail led to a dispersed distribution of rainfall.