Analysis of the physical mechanism of a persistent heavy rain event at Tongren in July 2014

Using data from automatic rainfall stations, NCEP/NCAR 1°×1° 6 hourly reanalysis and satellite TBB, the maintaining mechanism of a persistent rainstorm in Tongren from July 13 to 17 of 2014 was analyzed.The result showed that the northwesterly flow at the east of the stable Lake Baikal resistance high and behind the low vortex trough carried cold airmass to the south, which met the warm moist airmass southwest of the subtropical high periphery in northern Guizhou, leading to a persistent instability to the atmosphere in the region.At the same time, the upper anticyclonic circulation and lower vortex shear line formed a low-level rising and high-level sinking vertical circulation structure that further strengthened the development of the convective instability system.The dry cold air intrusion, which triggered several quick releases of convective instability energy, and the continuous supply of southwest warm moist air lead to the formation of torrential rain.Low-level low vortex system, steady surface convergence line, and torrential rain provided favorable dynamic condition.Continuous water vapor transport and convergence formation provided favorable moisture condition.Under this atmospheric circulation, severe convections formed at various regions repeatedly affected Tongren, causing continuous heavy rain.Furthermore, the effects of terrain blocking, lifting and converging by bell mouth further enhanced the development of the torrential rain event.