Combining triple-moment ice with prognostic liquid fraction in the P3 microphysics scheme: Impacts on a simulated squall line

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.