The Influence of Aerosols and Meteorological Conditions on the Total Rain Volume of the Mesoscale Convective Systems Over Tropical Continents

This study provides an observational assessment of the variations of the total rain volume (TRV) with aerosols through the entire lifetime of mesoscale convective systems (MCSs) over tropics. Using 70,000 MCSs' samples, we show that TRV increases with aerosols from clean to moderately heavy polluted conditions (aerosol optical depth [AOD] similar to 0.0-0.4). TRV decreases when AOD exceeds 0.5. The TRV change with AOD is strongest under favorable meteorological conditions, such as high total precipitable water (45-75 kg/m(2)), high convective available potential energy (1,200-2,400 J/kg), and intermediate vertical wind shear (9-21 x 10(-4)/s). TRV of MCSs increases from 2 to 4 km(3) (rain depth similar to 20-40 mm) when AOD < 0.15 or > 0.5, to more than 12 km(3) (similar to 120 mm) when 0.2 < AOD < 0.4 under above the mentioned optimal meteorological conditions. The basic response of TRV to aerosol concentrations is similar under all the meteorological conditions and during all stages of the MCS lifecycle. Plain language summary Mesoscale convective systems (MCSs) contribute to the largest fraction of global rainfall and are often responsible for devastating flood events. It has long been hypothesized that aerosols can enhance rainfall of MCSs by suppressing rainfall during the early stage of the convection, enabling more cloud droplets to rise to higher altitude and so freeze. Freezing releases more latent heat, which drives strong rising motion and so enables formation of large hydrometeors for heavy rainfall. Thus, it is central to evaluate rainfall changes with aerosols through the entire lifetime of the MCCs. This work provides a first observational assessment of the variation of the total rain generated by MCSs through their lifetime with ambient aerosols, under various ambient meteorological conditions over the global tropical continents. Our results show that aerosols have a strong invigoration effect on MCSs' total rainfall volume. Total rainfall volume increases as AOD increases up to 0.4 and decreases as AOD increases beyond 0.5. Such effects are similar throughout different phases of their convective lifecycle and under various meteorological conditions.