武汉市一次对流梅雨暴雨过程诊断分析

Diagnostic Analysis of a Convective Meiyu Rainstorm in Wuhan

2016年7月5—6日武汉市发生对流梅雨暴雨,出现严重城市内涝。分析对流云团活动、天气系统与物理量演变,结果表明:(1)对流云团来自江汉平原东部,暴雨前期对流云团合并发生在2个β云团之间,中期2个β云团先后与1个α云团合并,后期对流云团无明显合并,虽有向西的指状对流云生成,武汉市强降雨还是开始减弱。(2)暴雨发生在200hPa南亚高压东伸脊北侧,500hPa副热带高压在江南加强西进过程中,500hPa纬向切变转为低槽东移,850hPa江汉平原低涡则是迴旋少动,高空偏北风急流左侧水汽辐散与偏南风低空急流前方水汽辐合耦合有利于启动强降雨。(3)武汉站200~850hPa,500~850hPa风垂直切变明显,400hPa干空气入侵,共同触发了强降雨。

A convective Meiyu rainstorm took place in Wuhan from 5 to 6 July 2016,which caused serious urban water logging.The convective clouds influencing the weather system and physical elements are studied.The results show：（1）The convective clouds came from the eastern Jianghan Plain.During the heavy rain in Wuhan,twoβconvective cells merged at the first stage,and twoβconvective cells merged withαcloud successively at the second stage,in which rainfall in Wuhan strengthened dramatically.At the last stage,because the convective cloud cluster passed Wuhan without obvious merger,the heavy rainfall began to reduce,though there appeared the westward finger-like convective clouds.（2）The heavy rain took place while the subtropical high was strengthening and moving westward.During the rainstorm,Wuhan was located at the northeast side of the ridge stretching eastward from the South Asia high at 200 hPa.The zonal shear line turned to a trough and moved eastward at 500 hPa;the vortex maintained over the Jianghan plain at 850 hPa.It was a favorable condition for the heavy rain that Wuhan was in the water vapor divergence zone locating at the left side of the northerly wind jet at 200 hPa,coupling with the water vapor convergence zone in front of the low-level southerly jet at 850 hPa.（3）As the wind direction over Wuhan turned out to be northwest at 200 hPa,wind speed increased at 500 hPa,both vertical shear between 200 hPa and 850 hPa and between 500 hPa and 850 hPa increased dramatically.Dry air appeared at400 hPa.These three factors motivated the rainstorm to burst.