Operational Plan, Effect Verification, and Key Technical Settings for a Stadium-Scale Artificial Rain Reduction Experiment

To explore the key technologies of artificial weather modification for specific targets (e.g., a stadium) and improve the efficiency of artificial rainfall modification for major events, this study conducts an artificial rainfall reduction experiment for the closing ceremony of Nanjing Youth Olympic Games on 28 August 2014. Satellite retrievals, radar observations, sounding data, and other sources of information as well as Cloud and Precipitation Accurate Analysis System (CPAS) are used in this study. The main conclusions are as follows. (1) On 28 August 2014, a large-scale cumulus cloud system with mixed-phase stratocumulus and stratus precipitation was observed. This system was influenced by the weak shear of a low-level trough and the precipitation was dominated by cold clouds with dry layers between clouds. Thereby, we adopted the crystal-priming over-catalytic hypothesis and conducted a rocket-catalytic rain abatement operation at a certain distance (100–25 km) from the stadium. Rocket shootings of different intensities were implemented for two echoes that affected the stadium successively (two rounds of 15 rocket shootings within 15 min for an isolated weak echo IA; multiple rounds of 156 rocket shootings within 80 min for a strong echo IB). Amazingly, after the shootings with the catalysis in the air, reflectivity of the two echoes was reduced at all altitudes with the most significant reduction at the 2-km altitude, and the time needed for the obvious reduction was 40 min. The most obvious reduction of the two echoes then maintained for 60 and 53 min, respectively, and the operation time needed for the echo zone to recover after the stop of rocket shooting was 108 min for echo IA and 90 min for echo IB. The two echoes moving across the stadium during the time period of the closing ceremony (2000–2130 local time) were at their minimal strengths, with almost no echo over the target stadium. This demonstrates that the rocket shooting strategy of over-crystallization catalysis is effective, and the shooting site, time, and dose are reasonable. The following technical parameters were used during this experiment. At about 80–25 km away from the target stadium in the west, the rocket shooting lasted for 15–80 min and the doses were not less than 1 shot min⁻¹ (1 shot min⁻¹ for echo IA, 2.25 shots min⁻¹ for echo IB). The attenuation rate was 0.21 dBZ min⁻¹ for the average 15 dBZ of echo IA. For the average 25 dBZ of echo IB, the attenuation rate was 0.27 dBZ min⁻¹. The above technical settings helped achieve the goal of reducing rain over the stadium to almost zero for nearly 1-h period during the critical time of the event.