An Extreme Rainfall Event in Coastal South China During SCMREX-2014: Formation and Roles of Rainband and Echo Trainings

In this study, an extreme rainfall event of 451mm in 20hr that occurred in coastal South China on 11 May 2014 during the Southern China Monsoon Rainfall Experiment is investigated using integrated observations from the dual-Doppler radar pair, polarimetric radar, extensive mesonetwork, and enhanced upper-air soundings. Results show the generation of the extreme rainfall by two consecutive mesoscale convective systems (MCSs) consisting of multiple meso--scale rainbands. The two MCSs are maintained by lifting southerly oceanic flows over a quasi-stationary mesoscale outflow boundary (MOB) along the coastline that are enhanced by convectively generated weak cold pool. Northeastward echo training of convective cells, under the influence of environmental southwesterly flows, leads to the formation of the multiple rainbands in each MCS. Their subsequent propagations in a rainband training form, together with the echo training, along the coastline account for the production of extreme rainfall. The second MCS is characterized with a leading bowing rainband showing a process of rapid splitting and reestablishment (RSRE), which contributes to the formation of the rainband training. The occurrence of the RSRE process requires ample supply of unstable upstream oceanic air mass, the quasi-stationary MOB, and a bowing rainband intersecting with the MOB. The second MCS produces more precipitation than the first one as a result of more rainbands, stronger convective intensity, and more moderate-sized raindrops with larger maximal sizes. The above findings, especially the RSRE process and its associated storm internal circulation, appear to add new Insights into the formation and maintenance of training rainbands and their roles in heavy rainfall production.