Aerosol effects on the development of a supercell storm in a double-moment bulk-cloud microphysics scheme

This study investigates the aerosol effects on the development of an idealized three-dimensional supercell storm, focusing on storm morphology and precipitation during a quasi steady state of a storm. The impact of the aerosol concentration on the simulated storm is evaluated by varying the initial cloud condensation nuclei (CCN) number concentration in the Weather Research and Forecasting Double-Moment Six-Class microphysics scheme. A right-moving, quasi-steady supercell with two diverging echo masses was reproduced, compared with the previous modeling study. In the experiment with a high CCN number concentration, storm intensity was weakened, and surface precipitation was reduced. On the other hand, the simulation that excluded the graupel substance produced a weaker low-level downdraft, thus less near-surface vorticity, compared with the simulation that included graupel. The CCN number concentrations did not affect the storm structures in the absence of graupel. In addition, the aerosol effects on the surface precipitation with respect to the initial CCN value were diametrically opposed. The major reason for the different responses to aerosol can be attributed to the exaggerated snow mass loading across the convective core when the graupel species is excluded. The results indicate that graupel species and related microphysics are crucial to the realistic representation of the aerosol-precipitation interactions within a supercell storm.