Impacts of aerosols on the environment triggering a tornado event in Yangtze River Delta, China

Extensive observational and modeling studies have demonstrated the influence of aerosols on convective storms and extreme precipitation, but their impacts on the environment triggering a tornado are virtually lacking. Here we examine such impacts for an EF3 supercell tornado on 14 May 2021, using the WRF-Chem model. To improve the simulation, we assimilate automatic weather station (AWS) ad Doppler radar observations into WRF-Chem model using a hybrid ensemble transform Kalman filter–three-dimensional variational (ETKF-3DVAR) data assimilation system. The simulation reasonably captures the storm motion, precipitation evolution and cold pool position, although their intensity are overestimated. PM 2.5 concentrations are underestimated, indicating the diagnosed aerosol effects are likely conservative. We found that aerosol effects reduce near-surface evaporative cooling by shifting updraft core away from region of strong rain evaporation, thereby weakening evaporative cooling within the updraft core. Moreover, aerosols enhance condensational heating in the 0.2-1 km layer. These two thermodynamic effects together increase microphysical heating and thermal buoyancy, thereby accelerating the updraft in the 0-1 km layer. As a result, the process amplifies convergence toward the updraft and deepens storm-relative inflow, thereby increasing the storm-relative helicity in the 0-1 km layer (SRH1), which dominates the enhancement of STP. Overall, anthropogenic aerosols render a more favorable environment to sustain a tornado. Our research provides more insights into aerosol thermodynamical and dynamical mechanisms, by which aerosols influence extreme weather.