等熵位涡在一次淮河流域大暴雨分析中的应用

利用NCEP/NCAR 1°×1°逐日再分析资料、常规气象观测资料,通过等熵位涡理论对淮河流域2009年9月24—25日的大暴雨过程进行分析。结果表明:淮河流域对流层低层的中尺度低涡的发生发展与此次暴雨密切相关;315 K等熵位涡高值中心的移动和强度变化很好地反映出中尺度低涡系统的发展变化情况,其移动方向与雨带走向一致,降水落区主要位于等熵位涡高值中心轴线移动方向右侧的强西南气流处,对应于345 K等熵面上干冷空气移动方向前部的暖湿区内;在暴雨发展强盛时期,淮河流域暴雨区上空从对流层高层至低层均存在明显的正等熵位涡平流,干冷空气的侵入使得低涡加强发展,辐合上升运动增强,有利于暴雨的增幅,这是引发此次暴雨过程重要的触发机制。

Application of isentropic potential vorticity in analysis of a rainstorm event over Huaihe River Valley

By using 1°×1° NCEP/NCAR daily reanalysis data and conventional meteorological observation data, the Isentropic Potential Vorticity (IPV) theory was adopted to analyze the heavy rainstorm event during 24-25 September, 2009 in Huaihe River Valley. Results show that the mesoscale low vortex system of the lower troposphere in Huaihe River Valley had a close relation with the occurrence and development of this heavy rainstorm. The movement and intensity variation of high value center of 315 K IPV revealed the development of the mesoscale low vortex system, whose moving direction was consistent with the rain band''s. The precipitation area was mainly located in the right side of high value center axis of IPV, where the strong Southwest jet appeared. Simultaneously, the dry cold air corresponding to the 345 K isentropic surface moved to the front of warm wet area. In the active period of development of the rainstorm, an obvious positive isentropic vorticity advection existed from the upper to the lower level of troposphere over the rainstorm area in Huaihe River Valley. The invasion of dry cold air led to the development of low vortex, the enhancement of convergence ascending motion and the increasing of heavy rain, which may be the significant triggering mechanisms for the heavy rainstorm.