承德市两次局地性短时暴雨过程的中尺度特征对比分析

Comparative Analysis on Mesoscale Characteristics of Two Local Short-Time Severe Rainstorm Processes in Chengde

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、5~10 min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1 h;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,6 m·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1 h,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。

On 17 June and 15 July 2014, two continuous local short-time severe rainstorms occurred in Chengde 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 con- vergence 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-3＇ 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.