一次低涡影响武汉短历时暴雨过程诊断分析

Diagnostic Analysis of a Short-duration Rainstorm Process Influenced by Vortex in Wuhan

选取1998年7月20-22日武汉短历时暴雨个例进行天气和诊断分析,揭示出四川盆地低涡分裂出小低涡沿暖切变东移至湖北长江沿线,在低涡东部生成中尺度对流云团,受低涡切变中强的上升气流影响,加之西南急流中携带的丰富水汽输入,导致中尺度对流云团一次次发生和发展,在武汉上空产生一次次短历时暴雨的主要成因。诊断分析还显示四川盆地至湖北东部有湿舌生成且稳定维持,武汉位于湿舌的东端;发生短历时暴雨时武汉上空比湿会突然增加;低涡消失或南压,925和500 h Pa比湿显著降低;湖北东北部至安徽一带有对流有效位能高值中心,这一高值中心（中心值2 700 J/kg以上）在低层对应着暖切变东部,武汉位于对流有效位能高值中心向西南方向伸展的梯度大值区。

Select 20 - 22 July 1998 in Wuhan Short-duration Rainstorm Case synoptic and diagnostic analysis revealed that the Sichuan Basin to split a small eddy vortex moved east along the warm shear along the Yangtze River in Hubei, in the eastem part of the vortex generation mesoscale convective cloud clusters, by the low vortex shear in strong updraft effect, combined with the rich southwest jet carrying moisture input, resulting in a time-scale convective cloud occurrence and development over the short duration Wuhan produce heavy rain again the main causes. Diagnostic analysis also shows that eastern Sichuan, Hubei wet tongue to generate and maintain stable, Wuhan is located in the eastern end of the wet tongue. Heavy rain occurs when a sudden increase over Wuhan wet, 925 hPa wet tongue root （eastern plateau to eastern Sichuan Basin） specific humidity of up to 21 g/kg or more, in the front end of the lower wet tongue up to 16 - 18 g/kg, 500 hPa up to 6 -8 g/kg, the vortex disappeared or southward, significantly lower than 925 hPa and 500 hPa wet. Another to the northeast, Hubei, Anhui CAPE with a high value of the center. The high value of the center （central value 2 700 J/kg or more） in the lower shear corresponds to warm the eastern （southwest and south- east airflow stream Interchange）, Wuhan is located CAPE high centers extending southwestward gradient large value area, CAPE values Wuhan l 800 J/kg before the start of the process of gradual reduction.