A numerical study of optical and physical properties of mixed-phase polar stratospheric clouds

A numerical model designed to describe the microphysics of stratospheric aerosols along an isentropic trajectory is employed to study optical and physical properties of mixed-phase polar stratospheric clouds (PSC). Particles size distribution is studied following the evolution of 1000 size bins. Solid particles are assumed to first form upon homogeneous nucleation of water ice. Heterogeneous formation of nitric acid trihydrate (NAT) and sulphuric acid tetrahydrate (SAT) is then assumed to take place only on the homogeneously nucleated ice particles. Two cooling rates, 10 K/day and 1000 K/day, representative in turn of synoptic and wave cooling events are employed. These lead to the nucleation of 0.1% and 80% of ambient aerosols, respectively. Following nucleation, the time evolution of PSC optical and physical properties is shown to be strongly influenced by the number of nucleated particles. The model-derived lidar backscatter ratio, depolarization ratio and extinction (all at 532 nm), plus distribution surface area and effective radius of equilibrium and non-equilibrium PSC are presented. These results provide links between polarization lidar observations and PSC composition and phase.