四川盆地一次中反气旋超级单体的雷达回波特征研究

Radar Echo Characteristics of an Meso-Anticyclonic Supercell of Sichuan in August 2016

利用成都多普勒天气雷达、风廓线雷达以及加密自动站资料,详细分析了超级单体的形成演变,以及中反气旋的形成原因,得到以下结论:中反气旋超级单体形成于高空冷涡西部的偏北气流下,中高层伴有强的冷平流,对流不稳定能量达到5029.7 J·kg-1,500~850 hPa温差达到29℃,500~925 hPa风切变矢量差约为16 m·s-1,探空整体呈现上干冷、下暖湿的喇叭口形状,低层逆温的存在利于能量的累积;地面偏西风在龙泉山脉的强迫抬升下触发雷暴,雷暴中下沉气流产生冷出流,在北侧不断触发新单体,雷暴与新生单体合并发展为超级单体。中反气旋超级单体风暴伴随低层强辐合、中反气旋、后侧入流、后侧入流缺口、涡旋偶等回波特征;S1超级单体风暴内中反气旋的形成由低层和中层两个部分合并形成。对于低层中反气旋,雷暴单体合并时产生小涡旋,干冷空气侵入与暖湿上升气流造成斜压涡度,使辐合产生旋转,在强辐合作用下雷暴强烈发展,强的上升运动使垂直涡度拉伸,旋转增强。中层中反气旋,3~4 km高度内水平涡度约为1.2×10-2 s-1,利于水平涡管的形成,在强的上升气流与下沉气流作用下产生涡旋偶,中高层风随高度逆时针旋转利于反气旋的发展。

The formation and evolution of the supercell that happened in Chengdu on 7 August 2016 were discussed.Based on Chengdu Doppler Weather Radar,wind-profiling radar,and densely laid-out automatic station observation,the contributing factors of the meso-anticyclone were studied in this paper.The results are as follows.The meso-anticyclonic supercell was formed under the northerly airflow in the west of the upper cold vortex,with strong cold advection in middle and upper levels.The convective instability energy(CAPE)reached 5029.7 J·kg-1,the temperature difference between 500 hPa and 850 hPa was 29℃,and the wind shear vector difference between 500 hPa and 925 hPa was about 16 m·s-1.The sounding as a whole took on the shape of a bell mouth,in which the upper level was dry and cold while the lower level was warm and wet.The existence of lower-level inversion was conducive to energy accumulation.Thunderstorms were triggered by westward winds under the forced uplift of Longquan Mountains,while downward flow produced cold outflow and triggered new cells continuously on the north side.Thunderstorms and new cells merged into supercell.The meso-anticyclonic supercell storm was accompanied by the echo characteristics such as low-level strong convergence,meso-anticyclone,rear inflow,rear inflow gap,vortex couple,etc.The formation of meso-anticyclone in S1 supercell storm was formed via merging the lower and middle levels.For low-level meso-anticyclones,small eddies were generated when thunderstorm and cells merged.The baroclinic vorticity was caused by the intrusion of dry cold air and warm wet updraft,which caused convergence to rotate.Thunderstorm developed strongly under strong convergence,and strong upward motion caused vertical vorticity to stretch,increasing rotation.For mid-level meso-anticyclones,the horizontal vorticity in the height range of 3-4 km was about 1.2×10-2 s-1,which was beneficial to the formation of horizontal vortex tubes.Vortex couples were generated under the strong updraft and downward airflow.The anticyclones were developed by counterclockwise rotation of mid-level and high-level winds.