Preliminary Study of the Mesoscale Numerical Simulation of the Rain Mitigation Operation during the Opening Ceremony of the 2008 Beijing Olympic Games

Strong convective clouds occurred in Beijing and its surrounding areas during the opening ceremony of the 2008 Beijing Olympic Games, which posed a threat to the ongoing ceremony activities at the National Stadium. According to the actual weather condition, rain mitigation by firing lots of special rockets was operated by the Beijing Weather Modification Office. The operation played a certain role in inhibiting the formation and development of cloud and precipitation. Based on the dynamic frame of MM5 and Reisner2 explicit cloud scheme, an AgI-seeding scheme is developed and used to simulate the rain mitigation operation which was carried out during 2005 LST-2012 LST. The seeding effect of the different seeding rate and the microphysical mechanism is analyzed. The results show that different seeding rates have much influence on the surface precipitation.When the seeding operation lasts seven minutes with seeding rate 5 g·s-1, the surface rainfall is suppressed in two hours and enhanced after two hours. The microphysical mechanism of the rainfall decreasing is the depletion of supercooled water after AgI is injected into the cloud, the graupel content decreases and then the rain water decreases. While the microphysical mechanism of the rainfall increased two hours after seeding operation is just because a positive feedback link is formed among the rain water, cloud water, graupel, and the temperature, which finally leads to the increase of surface rainfall. But it should be noted that for the limitation of the single-moment cloud scheme, the maximum rainfall reduction being of only 8%－12%, there is a certain gap between the goal of the rain mitigation and the simulation result. It is necessary to further simulation with the double-moment cloud scheme.