梅雨锋的典型结构、多样性和多尺度特征

利用自动站、FY-2E卫星、多普勒雷达及NCEP再分析资料等, 对2015年7月23日皖江地区一次最强梅雨锋大暴雨过程成因进行分析, 重点分析此次过程中短时强降水中尺度特征。结果表明:(1)此次过程是一次典型的梅雨锋对流性暴雨, 贝加尔湖宽广的高空槽及副高和大陆高压的稳定维持是引发大暴雨过程的大尺度背景条件。高空槽、西南涡、地面β中尺度气旋的维持和加强为大暴雨提供了强劲的动力和水汽条件。(2)此次暴雨过程低层辐合明显、高层辐散显著、中层上升运动强盛, 非常有利于低层中尺度涡旋的发生发展。(3)短时强降水发生于边界层辐合由弱变强且趋于最强的时段内, 超低空风速的显著增大对暴雨有着重要作用, 边界层的垂直风切变和700 hPa的干侵入增强了层结的不稳定性。强降水发生时低层锋生明显加强, 锋生函数最强中心的位置与大暴雨区基本一致。(4)短时强降水发生于α尺度对流云团团状中心和皖江西部特殊喇叭口地形处, 且位于地面β中尺度气旋右侧南风气流中。(5)强度弱、底部低、平均切变值小的中γ尺度气旋使低质心、移动缓慢的对流风暴更具组织性, 持续时间明显增加, 更易产生短时强降水。

Causal analysis of the strongest short-time rainfall process of meiyu front in Wanjiang in 2015

Based on data from automatic weather stations, satellite FY-2E, Doppler radar and NCEP reanalysis, we analyze the strongestheavy rainfall event of Meiyu front in Wanjiang on July 23rd, 2015, mainly the mesoscale features of short-time strong rainfall.Results are asfollows.(1) The event is a typical Meiyu front convective rainfall.The stable and persistent upper trough from Lake Baikal, subtropical highand continental high form the large-scale background conditions triggering the heavy rainfall event.The persistent and enhanced uppertrough, southwest vortex and ground beta mesoscale cyclone provide strong incentive and moisture conditions.(2) The rainfall event is characterized by clear low-level convergence and high-level divergence, and strong middle upward movement, which are favorable to the occurrence and development of low-level mesoscale vortex.(3) Short-time strong rainfall occurs within the period when boundary layer convergence is growing stronger and tends to be the strongest.The significant increase of super-low wind speed plays an important role in the heavyrainfall.The vertical wind shear in the boundary layer and dry intrusion at 700 hPa strengthen the instability of stratification.Low-level frontogenesis was significantly strengthened when the heavy rainfall occurred.Position of the strongest center of frontogenesis function is basicallycoincident with the heavy rainfall area.(4) Short-time heavy rainfall occurs in the center of the alpha scale convective clouds and the specialtrumpet-shaped terrain in west Wanjiang.It also is located in the southern flow at the right side of ground beta mesoscale cyclone.(5) The meso-γ scale cyclone, which is characterized by weak strength, low bottom and small average shear value, makes low centroid and slow-movingconvective storm more organized and its duration increased significantly.Thus short-time heavy rainfall is more likely to occur.