2014年河南一次晚秋暴雨成因分析

Analysis of a regional rainstorm in late autumn of 2014 in Henna

利用常规气象观测资料和NCEP1°×1°再分析资料,对2014年10月19-20日河南省一次晚秋暴雨的形成机制进行分析,结果表明:高纬冷空气沿贝湖低涡后部偏北气流南下,在河套地区形成低槽并携带冷空气东移,在河南境内与南支槽前强盛的西南急流汇合,导致了暴雨天气的出现。水汽通量势函数和辐散分量的辐合中心向暴雨区逐渐靠近,能体现水汽在暴雨区的汇聚,水汽通量的旋转分量在暴雨区气旋式环流的形成能较好地揭示降水集中发生时水汽的维持原因。在埃克曼非平衡流向埃克曼平衡流调整过程中,强迫边界层中产生较强的垂直上升运动,并在对流层中层强迫产生次级环流是此次暴雨过程发生发展的重要机制;同时,高空低空急流的耦合对Ekman非平衡流有一定的加强促进作用,形成Ekman非平衡流强迫的次级环流与高低空急流耦合产生的次级环流同位相叠加耦合的"双耦合"现象。"双耦合"现象的出现和对称不稳定能量的释放加速垂直运动发展,使上升运动从边界层一直延伸到对流层高层为雷暴的产生和暴雨的维持提供了良好的动力条件;中低层位涡异常扰动导致涡度强烈发展倾斜,可能是此次暴雨产生的重要原因。

Based on the conventional meteorological observation data and NCEP 1°×1°reanalysis data, the late autumn rainstorm process on October 19 to 20 of 2014 was analyzed, the results show that the high latitude cold air along northward flow in the back of the Lake Baikal Vortex moved southward to form the mid-latitude trough and move eastward with cold air, then meet with strong southwest jet, which led to the emergence of a rainstorm. The convergence centre of water vapor flux potential function and divergent component gradually close to the heavy rain area, which can reflect the convergence of water vapor in the heavy rain area. The formation of cyclonic circulation of the water vapor flux rotation component in the heavy rain area can reveal the maintenance of water vapor. During the adjustment of the Ekman non- balance flow in the boundary layer, there is a strong vertical ascending motion in boundary layer. Meanwhile, secondary circulation system at middle levels is triggered by the Ekman non-balance flow,this could be the important physical mechanism leading to this heavy rain events. Interconnection of middle-level secondary circulation strengthened the Ekman non-balance flow that triggered double Interconnection. The positive perturbation of potential vorticity in the lower layers is one of important factors for the formation and development of the heavy rain.