Relationship between aerosols, hail microphysics, and Z_DR columns

Mechanisms of formation of differential reflectivity columns are investigated in simulations of a midlatitude summertime hailstorm with hailstones up to several centimeters in diameter. Simulations are performed using a new version of the Hebrew University Cloud Model (HUCM) with spectral bin microphysics. A polarimetric radar forward operator is used to calculate radar reflectivity and differential reflectivity Z_DR. It is shown that Z_DR columns are associated with raindrops and with hail particles growing in a wet growth regime within convective updrafts. The height and volume of Z_DR columns increases with an increase in aerosol concentration. Small hail forming under clean conditions grows in updrafts largely in a dry growth regime corresponding to low Z_DR. Characteristics of Z_DR columns are highly correlated with vertical velocity, hail size, and aerosol concentration.