The role of ice-microphysics parametrizations in determining the prevalence of supercooled liquid water in high-resolution simulations of a Southern Ocean midlatitude cyclone

High-resolution simulations of a Southern Ocean cyclone are compared to satellite-derived observations of liquid water path, cloud-top properties, and top-of-atmosphere radiative fluxes. The focus is on the cold-air-outflow region, where there are contributions to the hydrological budget from the microphysical growth of ice particles by riming and vapor deposition and transport by turbulent mixing. The sensitivity of the simulation to the parameterization of these processes is tested and the relative importance of ice-nucleation temperature is identified. It is shown that ice-phase microphysics is a key factor determining the phase composition of Southern Ocean clouds and physically reasonable parameterization changes are identified that affect the liquid water content of these clouds. The information gained from the sensitivity tests is applied to global model development, where it is shown that a modification to the riming parameterization improves climate mean-state biases in the Southern Ocean region.