沙澧河流域两场大暴雨过程的对比分析

利用常规观测资料、自动站资料和NCEP1°×1°再分析资料对2007年7月5日和14日沙澧河流域两场大暴雨过程进行了诊断对比分析.结果表明:不同影响系统下产生的大暴雨过程其动力机制有所差异.垂直螺旋度计算结果显示:两次过程700hPa等压面上正垂直螺旋度中心的移向和强度变化与降水落区及趋势变化有很好的对应关系,暴雨区出现在正垂直螺旋度中心移动的前方,对流域大暴雨的落区有一定的指示意义.5日呈现中低层正、高层负的垂直螺旋度配置,动力条件更有利于大暴雨的发生.湿位涡演变分析发现,5日中低层既存在对流不稳定,又存在对称不稳定,有利于垂直对流和倾斜对流发生,造成流域大暴雨.14日中低层大气处于对流稳定状态,但边界层和中层存在对流不稳定,同时中层还存在较强的对称不稳定,垂直涡度得到较大增长,导致上升运动的加强和水汽的垂直输送,有利于降水增幅.

Comparison of Two Heavy Rainfall Events in Shali River Basin

Based on the conventional and automatic observation data, NCEP(1°×1°) reanalysis data, the causes of two heavy rainfall events occurred on 5 and 14 J uly, 2007 in Shali river area are diagnosed and analyzed. The diagnostic results show that the dynamic conditions of two heavy rainfall events are different und er different influencing systems. The results show that the movement direction a nd intensity transformation of the positive center of the vertical helicity at 7 00hPa matches the heavy rainfall regions quite well in two heavy rainfall events . The heavy rainfall center lies on the front of the movement of the vertical he licity center. The vertical helicity value is positive at lower level while negative at upper level on July 5, whose dynamic c ondition is more beneficial for the occurrence of the heavy rainfall. The moist potential vorticity analysis indicates that the atmospheric instability at lower level of JUL-5 heavy rainfall event is not only convectively unstable but also symmetrically instable, which is favorable for the development of both vertical convection and slantwise convection. For the JUL-14 event, the lower level atmos phere is convectively stable and the boundary layer is convectively unstable. At the same time, the middle-level atmosphere is convectively unstable and has obv iously symmetric instability, so the slantwise vorticity gets a bigger growth, w hich leads to the strong ascending movement and the moist air upward transport a nd makes the precipitation intensity increase.