Tentative discussion on the impact of aerosol on cloud and precipitation over Shanghai and its surrounding areas

Based on retrievals from the moderate-resolution imaging spectroradiometer (MODIS) abroad on satellite Aqua and Terra from April 2000 to September 2013 and rainfall records from automatic weather stations, we investigated the long term statistical properties of aerosol optical depth (AOD) over Shanghai and its surrounding areas. Then we analyzed the relationship between AOD and feature parameters for different types of clouds and surface precipitation. Lastly, we studied the interaction between aerosol and cloud and precipitation. Results show that the annual mean AOD has an increase and a decrease trend from 2000 to 2009 and 2011 to 2013, respectively, but a significant decrease in 2010 over Shanghai and its surrounding areas. With the increase of aerosol, the occurrence frequency of shallow liquid clouds reduces by 15.5%-32.4%, while that of deep mixed-phase clouds enhances by 2.1%-10.0%. The effect of the increasing aerosol loading on cloud liquid effective radius strongly depends on the environmental moisture conditions. Increasing aerosol loading tends to enhance (reduce) the liquid effective radius with sufficient (insufficient) moisture. The cloud top temperature of deep mixed-phase clouds decreases significantly with the increase of AOD. When aerosol loading is high, the occurrence frequency of relatively weak precipitation (hourly precipitation of less than 1.0 mm) reduces, while that of relatively strong precipitation (hourly precipitation of more than or equal to 1.0 mm) enhances, which indicates that the increase of aerosol loading will inhibit the occurrence of weak precipitation but strengthen that of strong precipitation.