雷暴单体合并进行中雷达回波参数演变及闪电活动的特征分析

雷暴单体合并是促使对流系统成长、增强、持久的重要因素,合并与灾害性天气有着密切的关系。针对23次合并样本（其中有闪电活动的样本10例）,利用多普勒雷达和Safir3000闪电定位系统的探测数据,基于雷达回波参数的构建与计算,分别以一次冰雹暴雨过程和一次强降水过程为例,对合并及雷暴系统的演变进行了物理过程分析,对所有样本特征进行了统计归纳。最后发现并验证了雷达回波参数F_V40up-6（即6 km以上对流单体大于40 dBz体积的变率）常常在合并进行中出现突然减小现象,简称为"突降";同时揭示了合并进行中闪电活动的特征。具体结论如下:（1）就合并最初开始位置而言,高度在5 km之下的样本最多,比例达86%。从合并用时看（即RHI图中30 dBz回波开始衔接至最强回波合为一体为止）,全都在6-36 min,其中用时在12 min以内的占56.5%;达到30 min的仅占16%。合并开始后,在97%的样本中,回波参数V₄₀（即大于40 dBz的总体积）、V_40up-6（即6 km以上大于40 dBz的总体积）出现增大;V₄₀增幅为7%-590%,V_40up-6增幅为3%-638%;V_40up-6最大值出现时刻距合并开始时刻12-18 min的,占总样本的60.1%;24-36 min的,占总样本的34.8%。（2）在雷暴单体合并进行中有"突降"现象的,占总样本的87%;其中又有77%的"突降"出现在距合并开始后的6-18 min内。（3）在10个闪电活动样本中,有9个样本在合并开始后,闪电频数出现了"跃增",甚至出现峰值;全部样本中参与放电的主正电荷区高度随着"突降"均有下降,降幅在1-4 km,而此时的闪电频数几乎没有变化。 

Evolution of radar parameters and lightning activity during thunderstorm cells merging

The merging of thunderstorm cells not only plays a very important role in the growth, intensification and maintenance of convective systems, but also has a close relationship with the development of severe weather. This paper analyzes the merging processes of a hailstorm event and a heavy rainstorm case respectively and summarizes the features of multiple samples. In total 23 samples are used. Detections of Doppler radar and SAFIR3000 lightning location system are selected for the present study. The method of radar parameters reconstruction is implemented to verify the phenomenon of "dump", which is the phenomenon that the volume of a convective cell with more than 40 dBz above 6 km often experiences a sudden decrease in the process of merging, and to reveal the lighting characteristics during the "dump" process. The results indicate that: (1) At the initiation of merging, most of the samples are below 5 km, which account for 86% of the total. From the perspective of time-consuming (from the time when the 30 dBz begins to converge to the moment when the strongest echoes merge into one), all the samples fall within the range of 6-36 min. The merging time is less than 12 min for 56.5% of the samples, while no more than 16% of the samples take 30 min for merging. After the beginning of merging, radar parameters of V₄₀ (total volume above 40 dBz) and V_40up-6 (total volume with more than 40 dBz over 6 km) experience increasing for 97% of the samples, and V₄₀ increases by 7%-590% and V_40up-6 increases by 3%-638%; 60.1% of the samples have the maximum value of V_40up-6 appearing between 12-18 min, and 34.8% of the samples have the maximum value appearing between 24-36 min after the initiation of merging. (2) 87% of the samples demonstrate the feature of "dump" during the merging process, which occurs within 6-18 min after the initiation of merging for 77% of the samples. (3) In the 10 lightning samples, the lighting frequencies of nine samples experience "jump" or even reach the peak after the initiation of merging. The height of the main positive charge region of all samples decreases to some extent following the "dump" with the decreases within the range of 1-4 km, but the frequency of lightning remains almost unchanged.