Improvements in PSTD methods and surface roughnessmodel applied to simulation of lidar-observable optical properties of roughened hexagonal crystals.

Understanding the fundamental scattering properties of ice atmospheric particles such as ice crystals and aerosol particles in clouds is important for proper interpretation of satellite observations and for development of radiation parametrizations in climate models, as is well known. Also well known are the increasingly severe CPU demands involved in attempts to numerically simulate just single particle scattering properties with exact methods when the particle size parameter increases. In this talk we will show results obtained with an improved version of our PSTD code that makes larger particle sizes accessible than before, together with a new model of specifying the degree of particle surface roughness. The particular application we concerns an issue of importance to lidar observations: the effect of particle morphology of ice crystals on lidar ratio, backscatter, and depolarization ratio.