“080527”湖北老河口短历时暴雨的中尺度天气成因分析

以2008年5月27日发生在湖北老河口的短历时暴雨为例，利用NCEP客观再分析资料，开展中尺度天气系统诊断分析。结果表明：干线、500 hPa冷温度槽、冷切尾部辐合区、中低层湿区及地面风场辐合线等中尺度天气系统的活动与暴雨发生、发展密切相关。干空气自北向南、自上而下侵入湿区，具有典型的湖北干侵入暴雨特征。干侵入使干冷空气与暖湿空气汇合上升，同时激发冷切尾部辐合区中的正涡度柱沿假相当位温锋区向上发展，配合地面中尺度辐合线，增强对流上升运动。500 hPa冷温度槽活动及干侵入造成垂直方向上对流不稳定，冷式切变线尾部由于冷暖平流、干湿平流交汇构成水平方向不稳定区，不稳定区受露点锋生扰动，从而触发强对流天气。中低层深厚湿区的维持和水汽辐合为老河口中尺度暴雨提供了水汽来源。

Formation reason for mesoscale weather system of a short-time rainstorm on May 27,2008 at Laohekou of Hubei province

Based on the NCEP reanalysis data, the mesoscale weather systems of a short-time rainstorm process oc- curred on May 27,2008 at Laohekou of Hubei province were analyzed. The results show the movement of me- soscale weather systems of a short time rainstorm such as dry line, cold trough at 500 hPa, convergence zone of rear of cold shear line, wet area at middle and low levels and convergence line of ground wind field and so on are closely related with the occurrence and development of heavy rain. Dry air invades the wet area from north to south and from upper to lower, which is of typical features of rainstorm caused by dry invasion in Hubei province. Dry invasion makes dry-cold air and warm-wet air rising jointly, and it causes the positive vorticity at the convergence area of rear of cold shear line developing upward along the front area of 0se, which enhances convective ascending motion in coordination with ground wind field convergence. Cold trough at 500 hPa and dry intrusion result in con- vective instability, and the convergence of cold-warm advection, dry-wet advection at the rear of cold shear line forms the unstable region at the horizontal direction. The unstable region is disturbed by dew point front,so con- vective weather is triggered. The sustainability of deep-wet area at middle and low levels and water vapor conver- gence provide the water vapor source for this process.