陕西中部一次致灾暖区大暴雨的中尺度特征及成因

Analysis of the convective characteristics and mechanism of a local heavy rainfall in Guanzhong of Shaanxi

摘要:

2022年7月14-15日陕西关中蒲城发生致灾特大暴雨，全球模式和中尺度模式漏报。利用高空观测、自动气象站、卫星、雷达、欧洲中心ERA5再分析资料等对中尺度对流系统的组织结构特征及成因进行分析。结果表明：此次暴雨过程发生在副高边缘暖区中，降水前环境场具备高湿高能及不稳定条件。极端降水由α、β和γ中尺度对流系统共同造成，暴雨云团经历两次后部对流新生、再次旺盛发展的过程。第一阶段β中尺度对流单体发展旺盛，低层偏东风加强带来持续高效的水汽辐合，中等强度的垂直风切变维持及增强造成热力垂直螺旋度增长，导致强涡旋运动维持，是暴雨云团合并增强组织化发展的重要机制。第二阶段由α中尺度暴雨云团后部新生的γ中尺度对流单体造成，该系统尺度小但生命史长，上冲云顶高，雷达风场气旋式辐合维持导致低质心、高云顶的倾斜深厚湿对流单体后向传播进而产生持续高效的降水是导致陕西关中东北部蒲城极端强降水的直接原因。

Abstract:

Using FY-4A satellite and radar data, regional automatic station data, European Center ERA-5 reanalysis data, the organizational structure characteristics of the mesoscale convective system at the edge of the subtropical high in the northeast of Guanzhong, Shaanxi Province on July 14-15, 2022 and the causes of the local special heavy rainstorm were studied. The results indicated that the extreme precipitation was caused by α,β and γ mesoscale convective cells. The northeast of Guanzhong is located in the warm zone of the Subtropical High. The shear of the 700 hPa low-vortex was maintained in the central and northern parts of Shaanxi, with unstable environmental conditions of high temperature, high humidity near the surface. The strengthening of low-level easterly wind brought about continuous water vapor convergence, the maintenance and enhancement of medium intensity vertical wind shear caused helicity growth, and the maintenance of strong vortex movement were important mechanisms for the consolidation and enhancement of rainstorm cloud clusters. The backward propagation of mesoscale convective cells was caused by the cyclonic convergence and maintenance of radar wind fields, resulting in the "train effect" of the backward propagation of inclined deep moist convective cells with low centroids and high cloud tops. The continuous and efficient precipitation was the direct cause of the heavy precipitation in Pucheng, northeastern Guanzhong, Shaanxi.