Combining Triple‐Moment Ice With Prognostic Liquid Fraction in the P3 Microphysics Scheme: Impacts on a Simulated Squall Line

Abstract

Abstract The Predicted Particle Properties (P3) bulk microphysics scheme has been recently modified to combine the two major innovations. The triple‐moment approach to represent ice, allowing for a freely evolving spectral dispersion of the size distribution, is combined with the predicted liquid fraction, which enables an explicit representation of mixed‐phase particles. The impacts of this combination are examined in the context of high‐resolution (1‐km horizontal grid spacing) simulations of an observed mid‐latitude squall line using the Global Environmental Multiscale atmospheric model. The simulation of mixed‐phase particles results in a faster squall line propagation speed and stronger cold pool due to greater cooling from the microphysical processes of sublimation, melting and evaporation. There is a reduction in the mass of ice reaching the surface resulting from a decrease in the mean size of melting ice particles aloft with the predicted liquid fraction. Compared to the original double‐moment configuration, triple‐moment P3 configuration results in larger mean ice sizes at the surface. The reflectivity structure is improved with the new version, now with a more pronounced bright band in the melting zone with the predicted liquid fraction.

Keywords

• predicted particle properties (P3)
• mixed‐phase particles
• triple‐moment ice
• equivalent reflectivity
• mid‐latitude squall line