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

Abstract

igh-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. We focus 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 parametrization 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 parametrization 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 parametrization improves climate mean-state biases in the Southern Ocean region.