一次特大暴雨过程中涡旋暴雨云团的演变特征分析

Evolution characteristics of vortex cloud clusters in an excessive torrential rainfall event

利用MODIS卫星、多普勒天气雷达和地面观测资料,对2013年6月30日四川遂宁一次特大暴雨天气过程中涡旋暴雨云团的演变特征进行了详细分析。主要结论是:(1)涡旋暴雨云团与其北侧的积云云团呈前倾结构,说明暴雨云团经历了先由弱积云发展为深对流云、再到云毡的逐步发展成熟过程;(2)涡旋暴雨云团从南到北围绕低涡中心东侧最多时有6条降水云带,其中南部的降水云带碰并增长带(-1^-10℃层)厚度大于凝结增长带(3^-1℃层)厚度,北部降水云带刚好相反,表明南部以碰并增长过程为优势物理过程,利于较快拓宽云滴谱,使得云滴迅速长大形成雨滴降落下来;(3)涡旋暴雨云团中最强降水云带位于其南部的资阳至遂宁一带,分析雷达回波垂直剖面图发现有8个对流单体分布在云带中,且不断有新生单体移向遂宁,并从南至北依次增强,形成"列车效应",其成熟阶段-10℃高度以下碰并增长很充分,厚度为6 km左右,-10℃高度以上存在一个深厚的冰相增长带,厚度5~8 km,发展到成熟阶段碰并增长和冰相过程均为优势微物理过程,云中碰并增长和冰化增长过程向下传递明显,这些特点利于快速形成降水,导致当日10—17时遂宁站连续出现强降水。

Evolution characteristics of vortex cloud clusters in an excessive torrential rainfall event occurred in Suining, Sichuan on 30 June 2013 are analyzed in detail by using MODIS satellite data, Doppler weather radar data and surface meteorological observations. The major re- sults are as follows. （1） The vortex cloud clusters caused the torrential rainfall. Many cumulus clusters in the north side presented a for- ward-tilling structure, which shows that cloud clusters accompanied by torrential rainfall experienced a transition from weak cumulus to deep convective clouds firstly and to cloud felt lastly. （2） As for vortex cloud clusters that caused torrential rainfall, there are six spiral cloud bands at most from south to north around the eastern side of the vortex center. The thickness of collision-coalescence growth （from-10℃ to-1℃） greater than that of the condensation growth （from -1 ℃ to 3 ℃） in the southern spiral cloud band as opposed to those in the northern spiral cloud band, which suggests that the predominant microphysical process is collision-coalescence growth during the development of southern convective cloud clusters, and then the cloud droplet spectrum is broaden faster to make the formation of cloud droplets grow rapidly into rain- drops while falling down. （3） The strongest spiral cloud bands locate in the southern area of vortex cloud clusters caused torrential rainfall from Ziyang to Suining. The eight convective cells are found in the southern spiral cloud band in the vertical cross section of radar reflectivity factor, and newborn cells moved continuously to Suining and strengthen in order from south to north, thus resulting in ＂train effect＂. During the mature stage of these cells, the collision-coalescence and condensation growth （thickness is about 6 km） are active below height of- 10 ~C level, and there is a thick ice growth layer （thickness is 5-8 km） above height of-10 ~C level. When these cells are mature, both collision-co-alescence growth and ice-phase are the predominant microphysical processes, and collision-coalescence growth zone and glaciations growth zone in the cloud propagate dramatically down to the lower levels from the development to the mature stage. These features are advantageous to the rapid formation of precipitation, and resulting in continuous severe precipitation in Suining fromlO：00 BT to 17：00 BT on 30 June 2013.