On 17 June and 15 July 2014,two continuous local short-time severe rainstorms occurred inChengde as a result of cold vortex.The hourly rainfalls were 39.6 and 66.1 mm · h-1 respectively and the maximum 10 min rainfalls were 15 and 18 mm correspondingly.Based on conventional observation data,5 -10 min automatic weather station data,Doppler radar data,satellite images and NCEP reanalysis data,the mesoscale characteristics of the two short-time severe rainstorms are analyzed in this paper.The minute precipitation observation reveals that in the 17 June rainstorm process,10 min rainfall showed a double peak type distribution as time going on,lasting about half an hour.In the 15 July rainstorm process,it showed a single peak type,which lasted less than 1 h.Both of the two local heavy rains were generated with the upper cold vortex circulation,and their triggering system is the ground mesoscale convergence center (convergence line).The precipitation peak was associated with southeast wind or the increased wind speed.The 6 m · s-1 southeast winds were favorable for the heavy rains.Satellite data show that the direct influence system of the rainstorm on 17 June 2014 was the meso-β scale convective system.The heavy precipitation was corresponding to the low area of TBB.The severe convective system on 15 July 2014 performed as the meso-γ scale,corresponding to the large gradient area of TBB.The rainstorm on 17 June 2014 corresponded to the merge enhancement of convective cell echoes,which had a horizontal scale of near 20 km,lasting about half an hour with the echo intensity of 65 dBz.The rainstorm on 15 July 2014 was shown that a number of convective cell echoes passed through the urban area of Chengde in order,due to the "train effect",and the convective cell echoes had a number of horizontal scales of less than 5 km,living less than 1 h with echo intensity 55 dBz.In two precipitation processes,the occurrence time of inverse wind area was corresponding to that of the short-time strong rainfall,the duration of inverse wind area was longer,and the rainfall intensity is also stronger.%2014年6月17日和7月15日,同样在冷涡系统影响下,河北省承德市区先后出现了两次局地性短时暴雨天气过程(小时雨强分别为39.6和66.1 mm·h-1,最大10 min雨强分别为15和18 mm).本文利用常规观测资料、5～10min加密自动站资料、多普勒雷达数据、卫星云图数据以及NCEP再分析资料,对这两次短时暴雨过程的中尺度特征进行对比分析.结果表明:分钟级降水观测显示,“6· 17暴雨”过程10 min雨量随时间表现为持续时间分别约为半小时的双峰型分布;“7· 15暴雨”过程降水呈单峰型,持续时间不足1h;两场局地暴雨是在高空冷涡环流背景下产生的,其触发系统均为地面中尺度辐合中心(辐合线),降水峰值与东南风或风速增大相关联,6m·s-1的东南风有利于强降水的维持.卫星资料显示,“6· 17暴雨”过程直接影响系统为β中尺度对流系统,强降水与TBB低值区对应,“7· 15暴雨”强降水对流系统则表现为γ中尺度,与TBB大梯度区对应.“6·17暴雨”过程对应水平尺度近20 km,生命史约半小时,回波强度达65 dBz对流单体回波的合并增强.“7· 15暴雨”过程则表现为多个水平尺度不足5 km,生命史不到1h,回波强度达55 dBz的对流单体回波依次经过承德市区,因“列车效应”造成.两次降水过程中逆风区的出现时间都与强降水时段有很好的配合,且逆风区的持续时间越长,产生的降水强度也越大.
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