四川盆地不同强度短时强降水物理量特征对比分析

Comparative Analysis on Characteristics of Physical Quantity of Flash-Rain Under Different Intensities in Sichuan Basin

利用2007-2017年5-9月四川盆地84个国家自动站逐小时观测资料和时间间隔6 h的ERA-Interim再分析资料,分析了四川盆地不同强度短时强降水发生发展所需的热力、水汽和垂直风切变等条件,并对不同强度短时强降水的环境物理量特征进行了对比。结果表明,极端短时强降水的抬升凝结高度、自由对流高度和平衡高度(EL)均高于普通短时强降水,EL可以较好地区分极端短时强降水和普通短时强降水,约75%的极端短时强降水和普通短时强降水分别发生在EL高于258.6和658.2 hPa的环境下。极端短时强降水的对流有效位能(CAPE)和对流抑制能量值同样高于普通短时强降水,约50%的极端短时强降水和普通短时强降水的CAPE值分别高于792.5和451.9 J·kg^(-1)。不同强度短时强降水的850和500 hPa假相当位温差(θse850-θse500)差异显著,极端短时强降水的θse850-θse500数值明显高于普通短时强降水,10℃可做为区分二者的参考阈值。约50%的短时强降水大气整层可降水量(PW)超过58 mm,不同强度短时强降水的PW差异不明显,但极端短时强降水具有较为明显的上干下湿垂直分布特征。垂直风切变和上升运动对四川盆地不同强度短时强降水的区分没有明确的指示意义。

Based on hourly observational datasets from 84 national automatic weather stations and 6 h ERA-Interim reanalysis data at Sichuan Basin between May and September during 2007-2017,this study investigates the ambient conditions,such as thermodynamic variables,water vapor and vertical wind shear,and contrasts characteristics of convective parameters of the occurrence and development of flash-rain under different intensities.Compared with ordinary short-time severe precipitation,extreme flash-rain has relatively higher lifting condensation level(LCL),higher level of free convection(LFC)and higher equilibrium level(EL),which can be used to effectively distinguish extreme and ordinary flash-rain.About 75%of extreme and ordinary flash-rain events occur in the ambient background with EL higher than 258.6 hPa and 658.2 hPa,respectively.The values of convective available potential energy(CAPE)and convective inhibition(CIN)are larger in extreme flash-rain events.About 50%of extreme and ordinary flash-rain occurrence needs CAPE values greater than 792.5 J·kg^(-1) and 451.9 J·kg^(-1),respectively.The bigger difference of potential pseudo-equivalent temperature between 850 hPa and 500 hPa(θse850-θse500)is better for extreme flash-rain,and 10℃can be the threshold value to judge extreme and ordinary flash-rain.The precipitable water(PW)value of about 50%of all flash-rain events is greater than 58 mm.The difference of PW between extreme and ordinary flash-rain is not obvious,but the vertical distribution characteristic of a dry upper level associated with a wet low level of extreme flash-rain is significant.The vertical wind shear can not act as a potential predicator to distinguish flash-rain under different intensities in Sichuan Basin,and the ascending motion can not either.