我国中东部不同级别短时强降水天气的环境物理量分布特征

Characteristics of environmental parameters for multi-intensity short-duration heavy rainfalls over East China

基于我国中东部2002—2009年5—9月逐小时降水观测资料和一天四次的NCEP最终分析资料,通过时空匹配处理,得到强度为20~49.9 mm·h-1(A类)、50~79.9 mm·h-1(B类)和不小于80 mm·h-1(C类)的短时强降水天气样本序列,逐类统计分析用于表征其发生发展环境条件的水汽、热力、抬升触发和垂直风切变等物理量的分布特征。结果表明:表征水汽条件的大气可降水量(TPW)对三类短时强降水有一定的指示意义,A、B、C类短时强降水必要的TPW值分别为27、32、42 mm,短时强降水量越大,其所需水汽含量越高。约50%的三类短时强降水均出现在TPW大于60 mm的湿环境中。表征热力、能量、动力和垂直风切变条件的物理量对三类短时强降水的环境条件区分并不显著,环境大气中水汽多少可能是决定短时强降水级别的必要因素。B类和C类短时强降水的高概率密度区域范围大致为TPW在55~70 mm之间、0—6 km垂直风切变在5~15 m·s-1之间,而C类短时强降水在TPW与最佳对流有效位能(BCAPE)以及0—6 km垂直风切变与BCAPE的概率密度分布图中均有两个显著高概率密度区,可能与CAPE影响高级别短时强降水产生的两种机制有关。

Based on hourly rainfall observations and 6-hourly final analysis from National Centers for Environmental Prediction(NCEP) over East China between May and September from 2002 to 2009 and using the spatiotemporal matching technique,we acquired the short-duration heavy rainfall samples of 20-49.9 mm·h^(-1)(Type A),50-79.9 mm·h^(-1)(Type B),and those exceeding 80 mm·h^(-1)(Type C),and then analyzed by type the spatiotemporal distribution characteristics of the physical quantities such as water vapor,thermodynamic variables,uplift triggering and vertical wind shear,which are used to characterize the environmental conditions of their occurrence and development.Results show that total precipitable water(TPW) characterized by water vapor conditions has certain significance for three types of short-duration heavy rainfalls.TPW values essential to Type A,Type B and Type C short-duration heavy rainfalls are 27 mm,32 mm and 42 mm,respectively.The higher the short-duration heavy rainfall is,the more water vapor content it needs.About 50% of all the short-duration heavy rainfalls happen in the wet environment of TPW greater than 60 mm.The physical quantities characterizing thermodynamic,energetic,dynamic and vertical wind shear are not significant for judging the environmental conditions of three types of short-duration heavy rainfall,which shows the amount of water vapor in the ambient atmosphere may be a necessary factor in determining the level of short-duration heavy rainfall.The high probability density range of Type B and Type C short-duration heavy rainfalls is approximately between 55 mm and 70 mm in TPW,and 5 m·s^(-1) and 15 m·s^(-1) in 0-6 km vertical wind shear.Additionally,Type C short-duration heavy rainfalls have two significant high probability density regions in the probability density scatter diagrams of the TPW vs.the best convective available potential energy(BCAPE),and the 0-6 km vertical wind shear vs.BCAPE,which may be related to the two mechanisms of CAPE affecting the generation of high-level short-duration heavy rainfalls.