Aerosol indirect effects on the temperature-precipitation scaling

Aerosols may impact precipitation in a complex way involving their direct and indirect effects. In a previous numerical study, the overall microphysical effect of aerosols was found to weaken precipitation through reduced precipitable water and convective instability. The present study aims to quantify the relative importance of these two processes in the reduction of summer precipitation using temperature-precipitation scaling. Based on a numerical sensitivity experiment conducted in central Europe aiming to isolate indirect effects, the results show that, all others effects being equal, the scaling of hourly convective precipitation with temperature follows the Clausius-Clapeyron (CC) relationship, whereas the decrease in convective precipitation does not scale with the CC law since it is mostly attributable to increased stability with increased aerosol concentration rather than to decreased precipitable water content. This effect is larger at low surface temperatures at which clouds are statistically more frequent and optically thicker. At these temperatures, the increase in stability is mostly linked to the stronger reduction in temperature in the lower troposphere compared to the upper troposphere, which results in lower lapse rates.