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气象:2011,37(2):142-155
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北京地区干湿雷暴形成机制的对比分析
(1.中国气象科学研究院, 北京 100081;2.北京市气象局, 北京 100089;3.中国气象局北京城市气象研究所, 北京 100089)
The Contrastive Analysis of Formation of Dry and Moist Thunderstorms in Beijing
(1.Chinese Academy of Meteorological Sciences, Beijing 100081;2.Beijing Meteorological Bureau, Beijing 100089;3.Institute of Urban Meteorology, CMA, Beijing 100089)
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投稿时间:2010-05-03    修订日期:2010-08-01
中文摘要: 利用多普勒雷达变分分析系统,结合局地非常规观测资料,对北京两次雷暴过程,即2008年8月14日湿雷暴(伴有强降水,简称“814”)和8月24日干雷暴(弱降水,简称“824”)形成的环境物理条件进行了较深入的对比分析,结果表明:(1) 影响“814”的天气系统,主要是高层500 hPa稳定的东北冷涡槽和与之配合的850 hPa切变线,850 hPa以下整层空气湿润,北京位于比湿值大于12 g·kg-1和地面相对湿度大于90%湿舌区,中低层具有由湿度差动平流引起的对流不稳定;“824”高层盛行平直的偏西风,低层有反气旋,地面有冷锋快速过境,850 hPa以下整层空气干燥,北京处于比湿小于6 g·kg-1和相对湿度小于30%区,中低层有明显的温度差动平流。(2) “814”北京上空存在较强的整层垂直风切变,500~1500 m风向随高度有明显顺转,增强低层暖湿入流,有利于雷暴迅速组织发展,整层合成风小,雷暴移速慢;“824”则相反,垂直风切变弱,没有明显的低层暖湿入流,不利于雷暴组织加强,整层合成风大,促使对流系统快速东移。(3) “814”是一次多单体雷暴相互影响,并相继碰撞合并的湿雷暴群事件,上游雷暴降水产生强的冷池出流与前方低层偏东风暖湿气流形成辐合线,迫使暖湿气流抬升,加上强热力不稳定和垂直风切变,有利于新对流单体产生,而多个雷暴冷池出流形成的阵风锋之间的相互碰撞,进一步加剧了这种不稳定,导致冷池之间雷暴新生或加强;“824”是一次伴随冷锋的线状对流系统快速东移过程,上游雷暴冷池出流阵风锋前沿没有明显的偏东风暖湿气流配合,缺少中尺度抬升机制和暖湿入流,新生雷暴难以生成和发展。
Abstract:Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.
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基金项目:公益性行业(气象)科研专项“京津冀城市群强对流天气短时临近预报关键技术研究”(GYHY200706004)资助
引用文本:
王婷婷,王迎春,陈明轩,张文龙,2011.北京地区干湿雷暴形成机制的对比分析[J].气象,37(2):142-155.
WANG Tingting,WANG Yingchun,CHEN Mingxuan,ZHANG Wenlong,2011.The Contrastive Analysis of Formation of Dry and Moist Thunderstorms in Beijing[J].Meteor Mon,37(2):142-155.