Distinct impacts on precipitation by aerosol radiative effect over three different megacity regions of eastern China

Abstract. Many studies have investigated the impacts of aerosol on the intensity and amount of precipitation, but few have been done so regarding the impacts of aerosol on the start and peak times of precipitation. Using the high-resolution precipitation, aerosol, and meteorological data in the warm season of June–August from 2015 to 2020, this study investigates the influence of aerosol on the start and peak times of precipitation over three different regions, the North China Plain (NCP), the Yangtze River Delta (YRD), and the Pearl River Delta (PRD). It shows that the period with the highest frequency of precipitation start time, defined as the frequent period (FP) of precipitation start time, is delayed and prolonged by aerosols in NCP, contributing to the similar durations of precipitation in NCP, YRD, and PRD. This study also shows that different types of aerosol (absorbing versus scattering) have caused different influences on the start and peak times of precipitation over the three study regions. The precipitation start time is 3 h advanced in NCP but 2 h delayed in PRD by aerosols during precipitation FP and shows no response to aerosol in YRD. Compared to stratiform precipitation, the convective precipitation is more sensitive to aerosol. The start and peak times of convective precipitation show similar responses to aerosols. This study further shows that the aerosol impacts on precipitation can vary with meteorological conditions. Humidity is beneficial to precipitation, which can advance the precipitation start and peak times and prolong the precipitation duration time. Correspondingly, the impacts of aerosol on start time of precipitation are significant under low humidity or weak low tropospheric stability conditions. The impacts of vertical wind shear (WS) on the start and peak times of precipitation are contrary to that of aerosols, resulting in the fact that WS inhibits the aerosol effects on precipitation.