2013年8月沙澧河流域一次连续暴雨过程成因分析

Cause Analysis of a Continuous Heavy Rainfall Process Over Shali River in August 2013

利用常规观测资料和NCEP 1°×1°再分析资料,对2013年8月24—25日河南省沙澧河流域的连续暴雨过程进行分析。结果表明:本次连续性暴雨过程共分为两部分,前一部分是台风"谭美"外围的螺旋云带导致,后一部分转为低槽切变线影响,转折点在24日20时之后。偏东急流为暴雨提供了充沛且持久的水汽条件,水汽通量高值区集中在800 h Pa以下的低层和边界层。垂直螺旋度计算结果显示,850 h Pa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,大暴雨中心位于正垂直螺旋度中心附近,正垂直螺旋度中心位置对大暴雨落区有一定的指示意义;中低层正、高层负的垂直螺旋度配置,动力条件非常有利于强降水产生。湿位涡演变分析发现,此次过程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,导致上升运动和水汽输送加强,有利于降水增幅。雷达回波演变特征表明,回波的后向传播、列车效应及准静止等特征,导致降水量增加,暴雨发展。

Based on conventional observation data and NCEP 1°×1°reanalysis data,the continuous heavy rainfall process occurred from August 24th to 25th,2013 in Shali river was analyzed.The results indicated that this continuous rainstorm process was composed of two stages,the first stage was caused by the spiral cloud band of“Tan Mei”,the second stage was caused by trough of low pressure and shear line,the turning point was after 20:00 August 24th.The easterly jet provided plentiful and lasting moisture,high water vapor flux was concentrated in the lower layer and boundary layer below 800 hPa.Result of the calculated vertical helicity showed that heavy storm center was located at the positive vertical helicity center at 850 hPa,and the movement direction and intensity change of the positive vertical helicity center matched rainfall area and trends of precipitation variations well,which to a certain degree can indicate the heavy storm area.Such dynamic conditions as positive vertical helicity at lower level while negative at upper level were very beneficial to the occurrence of heavy rainfall.Evolution analysis of moisture potential vorticity showed that there were convective and also symmetric instability at lower level,which is beneficial to the generation of vertical and slantwise convection,strengthening upward motion and moisture transport,enhancing precipitation at last.The characteristics of radar echo evolution indicate that the back propagation,train effect and quasi stationary lead to the increasing of precipitation and the development of rainstorm.