Abstract:

Based on conventional observation data，rainfall records from automatic meteorological station，numerical prediction products，FY － 2c /2d infrared satellite cloud images，the new generation Doppler weather radar data in Xifeng and NCEP re － analysis data，the rare torrential rain process occurred in east of Gansu from 22 to 26 July 2010 was diagnosed and analyzed． The results show that the rainstorm was caused by abnormal circulation，stable large － scale weather system，deep vortex between 700 and 300 hPa，deep vortex shear on 500 hPa，southwest jet stream，southeast jet stream and high level jet stream． There were newborn，developmental and incorporative meso － βand meso － γ cloud cluster on the east side of low vortex cloud band on satellite cloud images． During rainstorm processes，the radar echo intensity was not too strong generally and ranged from 35 to 40 dBZ，but the liquid water content was bigger and ranged from 35 to 40 kg·m－ 2 ，which was an obvious feature of continuous torrential rain echo． In addition，there was a good corresponding relation between rainstorm development and spatio － temporal evolution of vertical helicity，the heavy rain area appeared in the front of the moving center of positive vertical helicity，which has an indicative meaning to the regional torrential rainfall area．

Key words: Gansu, torrential rain, formation mechanism, helicity, cloud image, radar, dynamic conditions

摘要：

利用常规观测资料、自动气象站雨量、数值预报产品、ＦＹ ２２ｃ／２ｄ 红外卫星云图、西峰新一代多普勒天气雷达资料以及ＮＣＥＰ 再分析资料，对２０１０ 年７ 月２２ ～ ２６ 日发生在甘肃西北地区东部罕见大暴雨天气过程进行了诊断综合分析。结果表明：异常的环流，稳定的大尺度系统，７００ ～ ３００ ｈＰａ 深厚的低涡，５００ ｈＰａ“人”字型低涡切变及ＳＷ 急流、ＳＥ 急流和高空急流的共同作用下，造成甘肃平凉中东部罕见的大暴雨天气；卫星云图上表现为在低涡云带东侧不断有新生发展合并的中β、中γ 尺度云团；暴雨期间，雷达回波强度不是太强，在３５ ～ ４０ ｄＢＺ 之间，但液态水含量比较大，在３５ ～ ４０ ｋｇ·ｍ ^{－ ２}之间，这是持续大暴雨回波的一个明显特征。大暴雨的发生发展与垂直螺旋度的时空演变有很好的对应关系，大暴雨区出现在正垂直螺旋度中心移动的前方，对区域性大暴雨的落区有一定的指示意义。

关键词: 甘肃, 大暴雨, 发生机制, 螺旋度, 云图, 雷达, 动力条件