中文摘要：

2008年8月8日，在2008年北京奥运会开幕式举行之际，北京及周边地区出现了较强对流云团，给国家体育场内开幕式活动的顺利进行带来了极大威胁。根据云系的发展状况，北京市人工影响天气办公室有针对性地组织实施了大规模地面火箭人工消减雨作业，对抑制云、降水的形成和发展起到了一定作用。在中尺度数值模式MM5的Reisner2方案中引入了AgI粒子与云相互作用的过程，在MM5中实现了催化功能。参照2008年8月8日20：05至20：12进行的消减雨作业情况，利用加入催化方案的中尺度数值模式对该作业进行了数值模拟试验，就不同的播撒量对催化效果的影响进行了研究，并对其中的微物理机制进行了分析。研究结果表明：AgI播撒率对降水量改变影响很明显，当以5g·S^-1的速率持续播撒AgI7 min，在播撒作业后2h，催化区域内均表现为减雨，2h后为增雨。对于减雨的微物理机制主要是由于大量播撒AgI后导致空中云水大量减少，进一步导致霰减少，霰的减少导致雨水的减少；而2h后的增雨机制则是由于在雨水、云水、霰以及温度之间形成了正反馈，最终导致地面降水的增加。需要指出的是由于单参数方案的局限性，模拟的最大减雨率仅为8％～12％，离消雨的要求尚有差距，应利用双参数云方案作进一步模拟研究。

英文摘要：

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 EST. 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 decrea sing 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 necessa- ry to further simulation with the double-moment cloud scheme.