2011年6月湖北一次大暴雨灾害过程分析

Analysis on the process of a heavy rainstorm in Hubei in June of 2011

利用每6 h一次的美国国家环境预报中心(NCEP)FNL再分析资料,对2011年6月17—18日发生在湖北省的一次区域性大暴雨过程进行了诊断分析。结果表明,中低纬度、500 hPa为明显的东高西低环流形势,降水区位于高空槽前,处于700 hPa鞍型场中部;850 hPa在长江流域中游有明显的东西向切变线,降水区位于急流出口区左侧。强降水落区随着850 hPa水汽通量散度强辐合区的移动而移动,在水汽通量的大值区,降水强度也相对较强,强降水区都位于相对湿度≥90%的区域。强降水区上空对应着正涡度中心。在中低层对应着强辐合区,高层对应着辐散区。正涡度越强,伸展的高度越高;低层辐合越强,对应的降水强度也越强。垂直螺旋度正值中心与垂直速度负值中心所在区域有较强的降水。短时强降水需要高的K指数与高的A指数相配合,当K指数在36℃以上,A指数在20℃以上时,出现短时强降水的可能性很大。当只出现单一的K指数或A指数较大时,出现短时强降水的可能性较小。

By using the FNL reanalysis data every 6 hours,the diagnostic analysis of a regional heavy rain event in Hubei province from June 17 to June 18,2011 was conducted.The results show that in the middle and low latitudes,the 500 hPa is the east high and west low circulation pattern,the precipitation area is located in front of the upper trough,700 hPa is the middle part of the col field.850 hPa has an obvious east-west shear line in the middle reaches of the Yangtze river,located on the left side of the jet outlet area.The area with heavy rainfall moves with the convergence of the divergence of 850 hPa water vapor flux.In the large value area of water vapor flux,the precipitation intensity is also relatively strong.The areas with strong precipitation are all located in the area with relative humidity≥90%.The center of positive vorticity is directly facing over the strong precipitation area,There are strong convergence areas in the middle and lower layers,and divergence areas in the upper layers.With the increase of positive vorticity,the extension height increases.With the increase of low level convergence,the corresponding precipitation intensity also increases.The vertical helicity positive center and the vertical velocity negative center have strong precipitation.Short-term heavy rainfall requires a high K-index to match the high A-index.When the K-index is above 36℃and the A-index is above 20℃,there is a high probability of short-term heavy rainfall.When only a single K-index or A-index is large,it is less likely to have short-term heavy rainfall.