“02.6”陕南大暴雨的结构及成因分析

Structure and Causes of "02.6" Extremely Heavy Rain in the Southern Shaanxi Province

通过诊断分析发现:(1)“02.6”强降水与6月上旬越赤道气流和季风爆发密切相关,携带大量水汽的偏南气流与冷空气于6月8日交汇在西北地区东部,导致了这次强降水的发生;(2)与暴雨区相联系,存在横越低空急流的经向垂直环流,暴雨区处于该垂直环流的上升支;(3)偏南和偏东气流水汽通道在西北地区东部交汇,水汽的辐合积聚主要在对流层低层和行星边界层内完成;(4)整层的视热源<Q1>高值区在暴雨区附近呈东北—西南向分布,与切变线走向非常一致,降水产生的凝结潜热释放是强降水区大气的主要热源。同时,在大尺度上升运动区中低层存在一个条件对称不稳定建立的机制,使得在暴雨区,既存在深厚的热力不稳定机制,又存在水汽输入机制和热力不稳定的触发机制,从而形成强暴雨。

Using the NCEP reanalysis data, thermal and dynamical structures of heavy rainstorm in the southern Shaanxi province during 8-9 June 2002（02.6 ） are analyzed. Results show that the severe precipitation is closely related to the monsoon burst and the intensification of cross-equatorial flow, which bring plentiful water vapor and meet with cold masses at the eastern of northwest China on 8, June causing extremely heavy rain. There is a vertical secondary circulation crossing lower-lever jet whose ascending branch is at the area of heavy rain. The water vapor comes from southerly and easterly flow which converge at the eastern of northwest China with convergence mainly in lower levels＇ and PBL. The high value of the whole-level apparent heat source 〈Q1 〉 is near the area of heavy rain in the direction of northeasterly-southwesterly agreeable to shear line very well and the condensation latent heat releasing is main heat source with vertical advection item playing key role in Q1 and Q2. The construction of convection instability and conditional symmetry instability results that there is not only deep thermal instability, but also moisture influx and triggering mechanism of thermal instability causing strong torrential rain.