云南2次川滇切变线强降水过程对比分析

Comparative analysis of two heavy rainfall cases in Yunnan influenced by Chuan-dian shear line

利用探空、雷达和自动站观测资料等对2009年6月下旬川滇切变线影响下发生在云南的2次强降水过程进行对比分析,从大气环流形势特征、物理量条件和雷达产品特征等方面揭示2次过程的异同点.结果表明:川滇切变线南移影响云南时通常都有地面冷锋配合,锋面辐合抬升为强降水提供主要的动力条件.副热带高压西侧的西南气流源源不断地为降水提供水汽和不稳定能量,有西南低空急流配合时更有利于出现大范围强降水,强降水落区主要位于切变线及其南侧的风速辐合区;500 hPa引导气流对切变线的强度和移向有重要影响.即便前期700 hPa上切变线两侧高度场"北高南低"形势不明显,但在500 hPa中高纬为经向环流形势下,特别是有阻塞高压生成时,槽后脊前偏北气流有利于引导冷空气向南输送,使低层切变线加强并南移影响云南,造成云南全省性强降水过程.在此情形下,降水以层状-积云混合降水回波为主,且持续时间长、分布均匀.

Based on the characteristics of atmospheric circulation,physical quantity conditions and characteristics of radar products,two heavy rainfall cases in Yunnan on June 2009 influenced by Chuan-dian shear line were analyzed by using sounding data,radar data and automatic meteorological observing data.The sameness and dissimilarity between the two cases were revealed by comparative method.The results shows that there is a cold surface front usually with the Chuan-dian shear line moving toward the south and bring torrential rain to Yunnan.The frontal uplift supplies mainly dynamical conditions and the southwest air current lying west the subtropical high provides continuously water vapor and unstability energy for the torrential rain.The emergence of southwest low-level jet will help to intensify the front rain.In general the region of torrential rain is located nearby the shear line and south the shear line which there is convergence of wind speed.On the other hand the steering flow at 500 hPa has an important effect on the intensity and moving of shear line at 700 hPa.If there is meridional circulation position especially the development of Blocking Pattern in middle and high latitude at 500hPa,the north wind lying between trough-line and ridge-line of Blocking high will lead cold downdraft southward.which will strengthen the Chuan-dian shear line at 700 hPa and lead the shear line moving toward the south and bring torrential rain to Yunnan,even the height north of the shear line are almost same to the south previously.On this condition the precipitation echo has the characteristic of sheet-cumulus,the precipitation time is very long,and the precipitation intensity is changeless.