基于数值模拟对重庆西部地区一次强对流天气过程的成因分析

Analysis of Causes for a Convective Weather Event in Western Chongqing Based on Numerical Simulation

利用NECP/NCAR 1°×1°资料和地面加密站、卫星云图、多普勒雷达资料,分析了2011年夏季重庆西部一次强对流天气过程产生的天气背景、中尺度特征、不稳定能量、水汽条件和触发机制,并利用WRF数值模式输出的高分辨率资料,探讨了此次强对流天气的触发机制和演变规律。结果表明:此次对流天气以灾害性大风和短时强降水为主,并伴有局地冰雹。强对流发生前夕,渝西处于两高之间的低压区中,中高层有冷空气叠加低层低压,使强对流发生区域不稳定能量聚集;地面中尺度辐合线是触发强对流的关键因子,而其与冷池相互作用,加强了对流,使飑线系统发展。对飑线在成熟阶段的内部结构和温压场变化分析结果表明,飑线前方高湿的西南风低层入流,加强了对流云区的抬升,来自西北干冷的中层流入,在对流云区下沉,到近地面辐散流出,是造成地面灾害性大风天气的原因。

Using the NCEP/NCAR 1°×1°reanalysis data,surface densely observed data,satellite cloud images and Doppler radar data,this paper analyzes the weather background,mesoscale characteristics,unstable energy and water vapor conditions of a severe convective weather process that occurred in western Chongqing on 23 July 2011.Besides,based on the high-resolution data output by the WRF numerical model,the trigger mechanism and evolution rule of this severe convective weather are discussed.The results are as follows:The severe convective weather this time was mainly disastrous gale and short-time severe rainfall with parts of areas hit by hails.Before the occurrence of the severe convection,the west of Chongqing was in the low pressure zone between the Tibetan high and the western Pacific subtropical high.The cold air in the mid-and high-level developed downward and was superposed on the low-level warm air,leading to the unstable energy accumulated in the convective zone.The key triggering factor of the severe convective storm was the meso-scale convergence line on the surface,which interacted with the cold pool strengthening the convection and generating the squall line.Through analyzing the internal structure of squall line in its mature stage as well as the changes in temperature and pressure,the highly humid southwesterly wind in front of the squall line entered into the low level,enhancing the uplift of the convective clouds.The dry-cold air from the northwest in the middle level sank downward in the convective cloud area,diverging and flowing out near the surface.All these factors are the causes triggering the disastrous thunderstorm on surface.