Increase of precipitation by cloud seeding observed from a case study in November 2020 over Shijiazhuang, China
Human weather modification is a method to influence cloud developing process so that the precipitation becomes more beneficial to local human society. A long existing challenging issue is the quantification of the efficiency of cloud seeding. This study investigates the changes of cloud and precipitation properties after cloud seeding by using the observations from a comprehensive experiment carried out over Shijiazhuang, China on November 21, 2020. The precipitation events before the cloud seeding experiment make the atmospheric background with sufficient water vapor. Comparison of the cloud and precipitation properties between before and after the cloud seeding shows distinct changes in both cloud and precipitation properties based on observations from ground sites, aircraft, and satellite. The aircraft observations show that the cloud droplet number concentration and liquid water content decreased significantly, and the ice particle concentration and precipitation particle concentration increased significantly, after cloud seeding. The satellite remote sensing observations show a semi-circle with decreased cloud reflection in visible channel after cloud seeding. The ground weather radar shows increased radar reflectivity echos for clouds impacted by seeding, indicating the formation of precipitation. After cloud seeding, there are also two short-term precipitation events occurring in the periods of 04:54-04:56 and 05:26-05:34 UTC over ZhaoXian, and 05:05-05:14 and 06:13-06:22 UTC over NingJin on November 21, 2020, with total precipitation amount of 0.04 mm and 0.042 mm, respectively. All the research findings show robust evidences of conversion from liquid droplets to ice particles and increased precipitation by the cloud seeding during this experiment.