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Abstract:
In 2015 the Predicted Particle Properties (P3) bulk microphysics scheme was introduced, based on the concept that ice-phase hydrometeors can be represented by a single category, whose physical properties evolve continuously in time and space. Since its inception, P3 has undergone several major developments. Ice is now represented by a user-specified number of freely evolving categories, each with prognostic spectral dispersion, density, rime fraction, liquid fraction, and other properties. As such, P3 is a unique microphysics scheme which can, in principle, simulate a wide range of microphysical conditions. However, the impacts of certain aspect on the simulation of deep convection have not been fully explored.
This study examines the impacts of the liquid fraction and multiple ice categories on the simulation of hail in the context of near convection-resolving (250-m grid spacing) quasi-idealized simulations of two hail-producing supercell storms. All simulations use the triple-moment-ice configuration but varying the prognostic liquid fraction and the number of ice categories. The sensitivity to the initiation of new ice into specific categories and the merging categories with similar physical properties is also examined. The inclusion of liquid fraction significantly modifies the rates of melting and shedding and ultimately reduces the amount of ice reaching the surface. This has important implications for conventional 2-moment schemes. The increasing number of categories reduces “property dilution”, which occurs when two or more populations of particles with different properties are represented by a single category. This increases the amount of ice reaching the surface and the maximum hail size.
