北京奥运会开幕式期间的中尺度天气系统研究

Meso-scale Weather Systems During the Opening Ceremony of Beijing Olympic Games

利用北京地区稠密的地面观测网资料以及北京市观象台、海淀、上甸子3部风廓线仪的观测资料,通过分析2008年8月8日北京奥运会开幕式期间发生在北京地区的降水过程,讨论了此次过程中在环境风场、地形和城市热岛作用下,中尺度系统发展或减弱的可能机制及对城区降水的影响。结果表明:城市热岛和地形作用形成的次级环流圈对城区南北两侧的影响不同,在城区南侧,次级环流圈使南风减弱,同时受次级环流圈下沉气流影响,中尺度系统北上时会减弱;在城区北侧,次级环流圈使南风加强,中尺度系统南下时会使气流辐合增强,有利于中尺度系统发展。当环境风场是较弱的偏南风时,城市热岛-地形次级环流圈在城区1500 m以下形成辐合,以上辐散,在3000 m左右辐散最强,不利于北上的中尺度系统向城区发展形成降水。

The Opening Ceremony is one of the most influential events during 2008 Beijing Olympic Games.And the meteorological service of the Opening Ceremony is of great importance.The weather situation is very complicated,on one hand,analysis of upper air and surface layer circulation at 20：00 8 August suggests there is a great possibility of precipitation,on the other hand,the strong radar echo belts of the southeast area developed at around 21：20 begin to constantly move northward,which may combine with the strong meso-scale radar echoes from northeast,and lead to heavy rainfall in the urban area.But in fact,medium and heavy rainfall occurs in the southwest and northeast suburb,but almost no precipitation occurs in the urban area.The fact is beyond the explanation of conventional meteorological data.So high-resolution ground-based meteorological data observed by auto weather stations（AWS）,wind and temperature data from the surface layer to the tropopause observed by thee wind profilers located at Beijing Weather Observatory, Haidian Station and Shangdianzi Station are used.The possible mechanism of the meso-scale weather system developing and weakening which affects the precipitation in Beijing urban areas are discussed considering the influences of the environmental wind field,topography and urban heat island effect.It is concluded that the impact of secondary circulation loop formed by the heat island and topography effect to the south urban area is different from that to the north.In the south part of the city,the secondary circulation weakens the southerly,and its subsiding air weakens the northward branch of meso-scale system. But in the north part,the secondary circulation strengthens the southerly,and the air convergence will become stronger,promoting the development of meso-scale system.When weak southerly environmental wind exists,the secondary circulation loop will lead to air convergence below 1500 meters high.But the air divergence above the height of 1500 meters is unfavorable for the meso-scale system to develop northward and bring heavy rainfall to Beijing urban area.