A 1-D MODEL OF THE FORMATION AND EVOLUTION OF POLAR STRATOSPHERIC CLOUDS

A 1-D model of the formation and seasonal evolution of Polar Stratosph eric Clouds (PSCs) is described. The model considers PSCs of types 1 a nd 2 in the vertical range from 8 to 30 km and utilizes real temperatu re data. The micro-physical processes included in the model are the he terogeneous nucleation and condensation (or evaporation), while sedime ntation, gas diffusion and vertical wind velocity are the processes re sponsible for transport. Model simulations have been compared with PSC data obtained by lidar at the South Pole: results for the winter 1990 are discussed. The different contribution of type 1 and type 2 PSCs t o the measured backscattering coefficient has been evidenced. In the s imulations, layers of NAT particles form when low values of the backsc attering coefficient are measured; similarly, ice particles form when sharper and rapidly changeable structures with higher values of the ba ckscattering coefficient are observed. Significant results on the cond ensation and depletion of HNO3 and H2O are presented. Water vapor prof iles measured during winter 1990 are reproduced quite well.