Sensitivity study of the impact of CCN size on simulated ground precipitation for deep convection case

Abstract

A sensitivity study investigated the impact of the mean radius of the aerosol spectrum on surface precipitation using the two-moment bulk microphysical scheme. The numerical model solved the mixing ratios and corresponding number concentrations of the following seven hydrometeors: cloud droplets, raindrops, ice crystals, snow, graupel, frozen raindrops, and hail. Aerosol particles act as cloud condensation nuclei (CCN). The values of the mean radius of CCN varied from 0.01 μm to 1 μm, forming six sensitivity experiments. The mass production of various hydrometeors in the model domain and the amounts of surface rain and hail precipitation were analysed. Increasing the mean radius of the aerosol spectrum leads to an ever-widening of the precipitation area and a consequent increase in the amounts of rain and hail on the ground. The clouds that form in an environment characterized by a larger mean radius move faster and consist of multiple convective cells. In an environment with the smallest mean radius, there is a higher cloud droplet number concentration, which slows the transfer to rain via the autoconversion process. The higher amounts of frozen raindrops in the environment with larger aerosol particles lead to a pronounced source for hailstones, which further grows by accretion of cloud droplets. In such an atmosphere, a stronger melting of frozen raindrops and hail leads to faster conversion to the rain category compared to the cases with smaller aerosol particles.