Extent of aerosol effect on the precipitation of squall lines: A case study in South China

It remains unclear to what extent squall lines respond to aerosol particles serving as cloud condensation nuclei (CCN). To solve this problem, dozens of simulated cases formed by adding balanced perturbations to initial meteorological fields have been conducted to quantify the effect of the aerosol on hydrometeors, precipitation, and their related microphysical processes in this study. The results showed that the changes in total surface precipitation of squall lines to aerosol perturbations ranged from -14% to 4% in South China. Even if there was no significant change in total precipitation in some cases, the precipitation over partial area still showed obvious changes which were related to the degree of convective organization. Through cluster analysis, the sign of the precipitation response to increasing aerosol loading depended on whether the increase in graupel growth compensated for the loss of snow and rain growth under polluted conditions. With increased aerosol loading, more cloud droplets suppressed rain formation and subsequently rain growth due to lower collision-coalescence efficiency, and the snow growth was also suppressed by the decrease in the riming process. However, there was more graupel melting into rainwater due to an increase in graupel growth by accreting cloud droplets. Through composite analysis of meteorological fields, surface precipitation suppressed by aerosols was shown to be more likely to appear in poor water vapor conditions and weak convective intensities, and vice versa. Plain language summary: Anthropogenic aerosol, which is one of uncertain factors in global climate system and has increased with the development of industry, can serve as cloud condensation nuclei to influence the radiative budget of climate system by affecting cloud albedo, cloud microphysical structure, and precipitation. Quantified the impact of aerosol perturbation on precipitation is urgent for climate change impact study in China. Here, dozens of simulated squall lines with similar synoptic situations have been used to evaluate the sensitivity of squall line precipitation to aerosol particles, especially focused on microphysical processes. This will help to quantitatively investigate to what extent surface precipitation of squall line can be induced by aerosols and how it relates to meteorological elements.