台风远距离影响下江苏两次梅雨期暴雨过程对比分析

Comparison of Two Rainstorms Related to Distant Typhoons Affecting Jiangsu Province During Meiyu Period

台风远距离影响下江苏两次梅雨期暴雨过程(2001年6月和1986年7月,以下简称“01·6”降水过程和“86·7”降水过程)的对比分析表明:“01·6”降水过程暴雨持续时段集中、落区稳定、降水强度大;“86·7”降水过程暴雨持续时间长、落区自北向南移动、降水强度稍弱。环流形势方面,“01·6”过程副热带高压北抬明显,台风倒槽北伸与低空急流共同构成低层风场辐合、输送暖湿气流,中高层低压槽稳定少动,高层冷空气影响较弱;“86·7”过程台风倒槽北伸和影响程度均不及“01·6”过程,低空急流对低层风场辐合及暖湿气流输送贡献更大,中高层低压槽东移较快且均明显南压,高层冷空气影响较强。动力条件方面,“01·6”过程高层辐散、低层辐合更剧烈,上负下正的涡度配置更加稳定深厚,非地转湿Q矢量辐合更强,且动力配置均稳定于江苏东南部;“86·7”过程动力条件稍弱,且高低空散度耦合、垂直涡度配置由江苏中北部向东南部移动,非地转湿Q矢量辐合区覆盖江苏东部。水汽条件方面,“01·6”过程较“86·7”过程低层水汽通量辐合更强,暴雨区上空饱和程度更高、深厚饱和层形成更早、维持时间更长。热力条件方面,“86·7”过程中低层大气对流不稳定性更强,但“01·6”过程E指数及其增幅更大,即中低层大气能量更高、水汽含量更丰富。

A comparison of two rainstorms that ocurred in June 2001 and July 1986(hereafter“01·6”and“86·7”)related to distant typhoons affecting Jiangsu Province during Meiyu period shows that for“01·6”,the precipitation duration is shorter,the precipitation area is not changed,and the rainfall intensity is stronger,while for“86·7”,the precipitation duration is longer,the precipitation area moves from north to south,and the rainfall intensity is weaker.In terms of atmospheric circulations,during the“01·6”process,the subtropical high extends significantly to the north,the northward extending inverted trough of typhoon and the low-level jet jointly form the low-level convergence and transport the warm and moist air together,the low-pressure troughs at middle-and upper-level are stable,and the influence of upper-level cold air is weaker.Comparatively during the“86·7”process,the northward extension and impact of typhoon’s inverted trough are weaker,the convergence of low-level wind and the transportation of warm and humid air flow rely more on low-level jet than on the inverted trough of typhoon,the low-pressure troughs at middle-and upper-level both move eastward and southward quickly,and the influence of upper-level cold air is strong.In terms of dynamical analysis,the high-level divergence and low-level convergence of the“01·6”process are more intense,the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep,the non-geostrophic wet Q vector convergence is stronger,and all these dynamic processes stay over the southeastern part of Jiangsu.However,for“86·7”,the dynamic processes are weaker,the coupling of divergence and vertical vorticity move from north-central Jiangsu to the southeastern part of Jiangsu,and the non-geostrophic Q vector convergence zone covers eastern part of Jiangsu.Compared with“86·7”,the low-level water vapor flux convergence of“01·6”is stronger,the air over the rainstorm area of“01·6”is more saturated,and the deep saturated layer“01·6”is formed earlier and maintain longer.In terms of thermodynamical analysis,the convective instability of middle-and lower-level atmosphere is stronger,but the E index and its increment of“01·6”are greater,which demonstrates that the middle-and low-level atmosphere contains more energy and more water vapor.