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.