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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
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摘要: 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。Abstract: 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.
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Key words:
- urban heat island;
- topography;
- wind profile data
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图 1 2008年8月8日20：00环流形势
(a)850hPa散度场 (黑色等值线，单位：10-6s-1; 实线为辐散；虚线为辐合) 和垂直速度场 (彩色填充，负值表示上升运动)，(b)850hPa环流形势场 (蓝色实线，单位：dagpm)、温度场 (红色实线，单位：℃)、风场 (单位：1个风羽=4m/s) 和辐合切变线 (棕色实线)(红色圆点是鸟巢位置)，(c) 鸟巢上空的垂直速度廓线 (负值表示上升运动)，(d) 海平面气压场 (黑色实线，单位：hPa) 和过去6h降水量 (彩色填充)
Fig. 1 The circulation of atmosphere at 20: 00 8 August 2008
(a) the divergence field (black contour, unit: 10 -6S-1; solid line: divergence; dotted line: convergence) and the vertical velocity field (shaded, negative: upward motion) on 850 hPa, (b) the circulation situation of on 850 hPa (blue solid line, unit: dagpm), temperature field (red solid line, unit: C), wind field (unit:4 m/s) and the convergence line (brown solid line) (red dot denotes the location of the Olympic Center), (c) the profiler of the vertical velocity over the Olympic Center (the negative denotes the upward motion), (d) sea surface pressure field (black solid line, unit: hPa) and precipitation of the past 6 hours (shaded)
图 2 2008年8月8日北京车道沟多普勒雷达组合反射率因子
(红色圆点是鸟巢位置)(a)21：40，(b)22：43
Fig. 2 Radar composite reflectivity factor by Doppler weather radar in Chedaogou Beijing on 8 August 2008
(red dot denotes the location of the Olympic Center)(a) at 21:40, (b) at 22:43
图 3 2008年8月8日19:00—9日01:00北京地区降水量 (红色圆点是鸟巢位置)
Fig. 3 Total precipitation of Beijing area from 19:00 8 August to 01:00 9 August, 2008 (red dot denotes the location of the Olympic Center)
图 4 2008年8月8日13：54-23：54海淀站 (a) 和北京市观象台 (b)30min间隔风廓线图 (红色实线为切变线)
Fig. 4 Wind profiler map of Haidian Station (a) and Beijing Weather Observatory (b) atintervals of 30 minutes from 13:54 to 23:54 on 8 August 2008
图 5 地形对温度分布的影响 (a) 北京地区地形图和主要自动站分布，(b)2008年8月8日21：00北京地区等温线 (彩色填充) 和风场
Fig. 5 The effect of terrain to distribution of temperature (a) the map of terrain and the locations of some main automatic weather stations in Beijing area, (b) isotherms of Beijing and wind plot at 21:008 August 2008
图 6 2008年8月8日13：54-23：54根据海淀站风廓线计算温度平流 (正值为暖平流，负值为冷平流)(a) 及根据北京市观象台、海淀站、上甸子站风廓线计算散度 (b)
Fig. 6 Temperature advection of Haidian Station (positive: warm advection; negative: cold advection) (a) and divergence calculated from profile data of Beijing Weather Observatory, Haidian Station and Shangdianzi Station (b) rrom 13: 54 to 23: 54 8 August 2008 (b)
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