渭河流域两次暴雨过程中尺度诊断对比分析

A Comparative Analysis of Meso-scale Diagnosis in the Formation of Two Rainstorms in the Wei River Valley

采用25点低通滤波技术对2006年6月2—3日和2007年8月8—9日渭河流域两次突发暴雨过程环流形势和动力学特征进行了分析,探索渭河流域致洪暴雨形成的中尺度动力机制。结果表明:中低层(700～850hPa)中尺度切变线或辐合是这两次暴雨过程产生的直接影响系统,产生于滤波前中低层弱切变线左侧大约50～100km处;垂直运动的上升支两侧有对称分布的下沉运动中心相对应,证明了中尺度次级环流的存在。垂直次级环流圈的形成促进了上升支强烈上升运动的发展,为强对流和暴雨天气提供了良好的动力条件。随着中尺度次级环流缓慢向东北方向移动,强降水区逐渐向次级环流上升支的右侧扩展;正涡度中心向上伸展加强,表明中尺度气旋加深,增强,范围增大,有利于中低层气旋性环流的生成和发展,对暴雨的产生和维持起到了重要作用。

An analysis is made of the situation of circumfluence and dynamic characteristics in the formation of two sudden rainstorms in the Wei River valley between the second and third of June,2006,and between the eighth and ninth of August,2007 through the use of 25khz low-pass filter technique,and an exploration is made of the Meso-scale dynamic mechanism in the formation of storm in the Wei River valley.The findings are as follows.Middle and low layers（700～850hPa） Meso-scale shear line or convergence is the system which directly affects the formation of the two rainstorms,which occurs at approximately 50～100km to the left side of the weak shear line of middle and low layers in front of the filter.The uplift of vertical motion supports the flanks with symmetrically plunging motion centre,which proves the existence of Meso-scale secondary circumfluence.The formation of vertical secondary circumfluence circle facilitates the development of strong uplifting motion,which provides a good dynamic condition for strong convection and rainstorm weather.With Meso-scale secondary circumfluence slowly moving toward northeastern direction,strong precipitation area gradually expands to the right side of secondary circumfluence uplift wing.The stretch of normal vortex centre intensifies its upward expansion,which shows the reinforcement,deepening and scope expansion of Meso-scale cyclone,exerting an important role for the generation and maintenance of rainstorms.