南疆西部暴雨的动力热力特征分析

Dynamic and Thermal Characteristics on Rainstorm over the West of Southern Xinjiang

采用NCEP1°×1°再分析资料,对2012年南疆西部3次暴雨过程中的锋生函数和湿位涡特征的对比,分析南疆西部降水的动力、热力条件与降水的关系,结果表明:锋生函数和湿位涡与南疆西部的降水有很好的对应关系,并能较好地反映降水的动力、热力机制。西部翻山的和东部"东灌"冷空气与南疆盆地的暖空气冷暖交汇,形成锋生。低层锋生达6×10^(-9) K·s^(-1)·m^(-1)以上时,低层辐合叠加地形强迫提供动力作用,触发降水。锋生的强度与降水强度成正比。低层辐合,暖气团被抬升,中层锋生强度达4×10^(-9) K·s^(-1)·m^(-1)以上时,冷暖交汇的热力作用和水汽凝结,使降水维持,形成暴雨。暴雨时有>3 PVU的正湿位涡叠加于负湿位涡之上,低层负湿位涡<-3.0 PVU时易出现短时强降水。垂直分布上前倾结构形成对流性降水,后倾结构形成持续性降水。

Based on the NCEP1.x1.reanalysis data,the dynamic and thermal characteristics on rainfall were analyzed by contrasting the frontogenesis function and MPV of the3rainstorm over the west of southern Xinjiang in2012.The results showed that there is an obvious correspondence between the frontogenesis function,MPV and rainfall over the west of southern Xinjiang,and it can reflect the dynamic and thermal mechanism of rainstorm.Frontogenesis caused by intersection of the cold air crossing the mountain in west and westward-moving on low level and the worm air in south Xinjiang basin.The convergence and topographic forcing provide dynamic effect and trigger the rainfall,when the frontogenesis is greater than6伊10-9K·s-1·m-1in low-level.There was a positive correlation between the strength of frontogenesis and precipitation intensity.The cold and warm currents meet provide thermal action and water vapor condensation,then the rainfall maintain and cause rainstorm,when the low-level convergence,and warm air mass uplift,and the frontogenesis function in middle-level is greater than4伊10-9K·s-1·m-1.The positive moist potential vorticity(MPV)greater than3PVU overlay negative MPV during rainstorm,and short-time strong rainfall appears when negative MPV in low level is less than-3PVU.On the vertical distribution,the forward-tilting structure occur convective precipitation,while the backward-tilting structure generate continuous rainfall.