2010年5月6日重庆强对流过程的天气学分析

Synoptic analysis of the severe convection event on 6 May 2010 in Chongqing

利用常规观测、NCEP/NCAR再分析、FY-2E卫星、多普勒雷达以及自动站观测资料,对2010年5月6日重庆强风雹、暴雨天气过程进行了天气学分析。详细讨论了各尺度天气系统的发展演变及相互作用关系,并在此基础上提出了此次强对流发生的天气背景概念模型。研究结果表明:这次强对流过程发生在中纬度气旋、反气旋和高空槽增强发展的背景下,地面气旋与反气旋之间的冷锋也在南移中逐渐增强,而中纬度系统与西南地区低压和副热带高压间构成的鞍形场在重庆北侧造成锋生,一方面使得冷锋西段增强,另一方面通过次级环流与中层急流正反馈相互作用,加剧重庆中低层辐合抬升运动,既降低了大气稳定度,又为对流的触发形成提供了有利条件。与此同时,重庆低层始终位于西南地区低压东北部,偏南气流不仅输送了充足的水汽,其伴随的暖平流还与太阳辐射共同造成了重庆低层的显著升温,形成了条件不稳定层结。5月5日夜间冷锋移至重庆地区,锋面附近的强辐合造成了对流的初始发展,这一过程很可能与冷锋进入四川盆地后的下坡地形有关。另外,此次天气过程中副热带高空急流造成的强垂直风切变和高空辐散也为对流的强烈发展提供了有利条件。

With the use of conventional observations, NCEP/NCAR reanalysis, FY-2E infrared sat- ellite imagery, Doppler radar and automatic weather stations data, synoptic analysis is conducted of the severe convection event on 6 May 2010 in Chongqing, focusing on the evolutions of different weather sys- tems and their interactions. A conceptual model of synoptic background for this case is proposed. The re- suits show that this event occurred under the background that midlatitude cyclone, anticyclone and upper trough were growing. Between the surface cyclone and anticyclone, a cold front emerged and intensified during southward propagation. Moreover, the extratropical weather systems made up a deformation field with the cyclone in the southwest and the subtropical high which caused frontogenesis north to Chongqing. Consequently, not only the cold front intensified, but a positive feedback interaction resulted as well be- tween low level frontogenesis and midlevel jet via secondary circulation, which enhanced the lower level convergence and associated lifting over Chongqing, destabilizing the atmosphere and providing a possibleinitiation mechanism. Meanwhile, lower levels over Chongqing was constantly dominated by southerly wind in the eastern part of the southwest cyclone, which transported abundant moisture from South China Sea and provided a very warm environment in company with solar radiation, resulting in conditional insta- hility. Up to the evening of 5 May the cold front had arrived Chongqing and the strong convergence near- by eaused initial development of convection. It appears that the formation of the convergence directly re- sponsible for the storms initiation should be related to the downslope topography when the cold front en-