Effects of Intentional and Inadvertent Hygroscopic Cloud Seeding

In order to study possible effects of intentional cloud seeding and air pollution on clouds and precipitation, investigations were performed with the numerical weather prediction model COSMO (formerly called LM) using a sophisticated cloud microphysics scheme developed at the Institut fur Meteorologie und Klimaforschung. Simulations with this model system on the high performance computer (HP XC400) operated by the computing center at the University of Karlsruhe show that in a land-sea breeze situation, typical for wintertime in the Eastern Mediterranean, aerosols have a considerable impact on the amount and spatial distribution of precipitation at the ground. The results suggest that it might be possible to gain a significant amount of freshwater shifting precipitation from sea to land by seeding the clouds with hygroscopic particles. It could also be shown that the model system is able to reproduce the spatial and temporal evolution of a hailstorm that was observed in South-West Germany, producing realistic radar reflectivities and amounts of precipitation and hail. Sensitivity studies reveal that CCN concentration has a significant impact on the severity of the hailstorm.