Mesoscale numerical simulation on the precipitation enhancement of stratiform clouds with embedded convection

Weather Research and Forecasting Model (WRF) coupled with a silver iodide (AgI) cloud-seeding scheme was used to simulate a precipitation enhancement of stratiform clouds with embedded convection(referred to as “SEC” hereinafter) in Beijing on May 29th, 2012. The seeding effect and its mechanisms were analyzed, and several sensitivity tests were performed to investigate the effects of dust, seeding amount, and seeding position on clouds and precipitation. When an amount of 100 g AgI was seeded in the convective region of the case in this study, rainfall decreased from 0.5 h to 1.5 h after seeding, and then increased in the following 1.5 h. The increment of the surface rainfall is mainly resulted from the melting of snow and graupel. Among the four ice nucleation mechanisms, condensation freezing is the most dominant, followed by contact freezing, and the deposition nucleation was the weakest. The seeding amount of AgI had a strong effect on the rainfall enhancement, and a moderate seeding amount of about 500 g is suggested. A further increase or decrease of AgI leads to a decrease of rainfall enhancement. We also found seeding in the clean air had more remarkable effects than under the dusty condition. Regarding the seeding position, seeding in the convection region was more prominent in enhancing rainfall, followed by seeding the convection entry region, and seeding in the stratus region has the least effect. These results reveal the seeding microphysical processes of SEC providing a guidance for weather modification operations.