Assessment of Possible Precipitation Enhancement by Glaciogenic Cloud Seeding Using WRF: A Case Study

The effects of airborne silver iodide (AgI) glaciogenic cloud seeding on the ice nucleation process and enhancement of orographic precipitation is evaluated using the aerosol-aware Thompson-Eidhammer microphysics scheme. The scheme is coupled to the GOCART aerosol model and implemented into the WRF model. Applying the scheme, which takes into account the aerosols serving as ice nuclei, enables the WRF to explicitly predict the effects of changes in aerosol number concentration on the precipitation formation. The selected seeding project was conducted in March 2015 over the Shirkouh Mountain in the center of Iran. The results show that the increased number of aerosols increased the updraft and downdraft, as well as the clouded volume. Therefore, depending on the relative humidity in the upper levels the airborne cloud-seeding operation is simulated to increase or decrease surface precipitation. Simulation data show that the 24-hour accumulated precipitation increased to 9.52% downwind of where AgI particles were released. However, the simulated seeding outcome for the southern regions is a 4.1% decrease in precipitation.