Analysis of a Short-Time Extreme Precipitation Event in Chongqing Under Weak Synoptic Forcing
Based on conventional weather data, FY-2F satellite data, Doppler radar products, densely-observed data from automatic surface weather observation system and ERA-Interim 0.125°×0.125° reanalysis data, the ambient condition and evolution of the short-time extreme precipitation event in Chongqing on 19 April 2019 is analyzed. The results show that under weak synoptic-scale vertical motion, this severe rain process was formed by a quasi-stationary meso-β scale convective system (MβCS) over Qijiang River Valley and its vicinity. Before the development of the severe convection, the local water vapor was sufficient, and stratification instability which was established and maintained by the wetter low-level and the drier mid-high-level was prominent. With the terrain inclining from southwest to northeast, Qijiang River Valley, located in the transition zone from Yungui Plateau to Sichuan Basin, was surrounded by mountains on three sides. Flowing from the south side of the valley, the increasing meso-γ scale convective cell brought about heavy rainfall and cold pool in the river valley. The strong mesoscale temperature gradient between the cold pool and the eastern slope of the valley promoted the intense convergence of the near-surface southwest wind to the eastern hillside, which was advantageous to the eastward convergence of the convective cell and strengthening, then the convection was organized into an isolated MβCS. With the coaction of continuous enhancement of the cold pool, topography blocking effect, merging of two MγCSs and weak ambient flow, the MβCS moved slowly, finally resulting in the localized extreme short-time rainfall over Qijiang and Wansheng.