Effects of aerosols on drop freezing, size and structure of hail: application of the theory of time -dependent freezing and hail growth in a spectral bin microphysics cloud model

The theory of wet growth of hail is extended to the case of the inhomogeneities of surface temperature and of liquid coverage over the surface of the particle. The theory treats the heat fluxes between its wet and dry components and from the sponge radially through the liquid skin to the air. The new theory can parameterize the spheroidal shape of hail. Gradual internal freezing of liquid soaking the hail or graupel particle's interior during dry growth (‘riming') is treated as well. Results of the new scheme for time-dependent freezing are compared against laboratory measurements. Entire experiments performed for single hailstones in a wind-tunnel are simulated off-line for comparison. Good agreement of the theoretical prediction with observations is obtained. The algorithms of time-dependent freezing were implemented in a spectral bin microphysics cloud model of the Hebrew University Cloud Model (HUCM). Simulations of hail storms under different aerosol concentrations are performed. It is shown that increase in the aerosol concentration increases size of hail stones and affects the regime of hail growth. Aerosols also affect drop freezing, size and location of freezing drops.