2018年7月15—17日北京极端强降水过程三类对流风暴及其强降水特征分析

Characteristics of Three Types of Convective Storms During the Beijing Extreme Precipitation Event in 15-17 July 2018

2018年7月15—17日,北京遭遇当年入汛以来最强降水过程。该过程具有持续时间长、累计雨量大、局地雨强强等特点。针对小时降水量阶段性减弱的特征,对该过程不同阶段三类对流风暴及其强降水特点进行了对比分析。结果表明:16日凌晨副热带高压边缘暖区强降水主要由低质心型对流风暴造成,该时段暖湿层结深厚,垂直风切变较弱;对流系统具有类似热带强降水型风暴特征,加之“列车效应”影响,导致北京密云出现极端强降水;高质心型对流风暴出现在16日至17日凌晨,受高空槽和副热带高压共同影响,中层有干空气侵入,整层垂直风切变较强;对流系统存在悬垂结构特征,但局地性强、移速快,其造成的最大降水量要弱于低质心型对流风暴;混合型对流风暴对应17日高空槽过境的强降水,该时段能量和水汽条件较前期明显减弱;对流风暴的强度和降水量级在三类风暴中最弱。不同类型对流风暴对应的环境条件、结构特征及其移动传播特点决定了该过程不同阶段的降水强度和量级。

An extremely severe precipitation event took place in Beijing during 15-17 July 2018.This event was characterized by long duration,large accumulated precipitation amount and locally strong intensity.According to the features of hourly precipitation decrease stage by stage,the three types of convective storms and their precipitation characteristics are analyzed and compared.The results show that the extreme precipitation at the edge of the subtropical high in the morning of 16 July was mainly caused by the low-echo-centroid convective storms,during which the warm and wet layer was deep and the vertical wind shear was weak.The characteristics of convective storms,which were similar to the severe tropical precipi-tation storms,along with the impact of“train effect”were the direct causes for the extreme severe precipitation in Minyun District of Beijing.The high-echo-centroid convective storms mainly took place during the daytime of 16 to the early morning of 17 July,when the westerly trough and the subtropical high affected this area together.During this period,the dry air intruded into the middle layer and the vertical wind shear of the whole layer was stronger. The convective storms had some characteristics such as high-echo-centroid, draping structure, strong local features and rapid movement, and the maximum precipitation intensity caused by the high-echo-centriod convective storms was weaker than it caused by low-echo-centroid convective storms. Hybrid convective storms corresponded to heavy precipitation during the transit of westerly trough on the 17th July. Compared with the early stage, the energy and water vapor conditions during this period decreased significantly. The echoes and precipitation intensity of hybrid convective storms were the weakest of the three types. The intensity and magnitudes of precipitation in different stages of this process were determined by the corresponding environmental conditions, structural characteristics and moving propagation characteristics of different types of convective storms.