Impact of Cold Pool on Mesoscale Convective System for Extreme Rainfall over Xinxiang on 9 July 2016
Based on a variety of NCEP reanalysis data, conventional weather data, temperature of black bold (TBB) data from FY-2E satellite, Doppler radar products and densely observed data from automatic surface weather observation system, the mesoscale characteristics of the torrential rain process that occurred over Xinxiang on 9 July 2016 are analyzed. Furthermore, the formation mechanism of the cold pool is revealed and its impact on mesoscale convective system (MCS) produced extreme rainfall is studied. The results show that: the back-building-quasi-stationary and vortex-shaped MCS, with low-qualify core structure, led to the extreme severe rain over Xinxiang. The cold pool outflow, caused by stratiform precipitation and convective precipitation, led to the surface convergence, and furthermore, the surface convergence triggered and intensified the convection. MCS obtained unstable energy from the dense zone of surface potential pseudo-equivalent temperature formed by cold pool flow and ambient wind. The cold pool outflow and ambient wind were similar in strength, resulting in a stable dense zone of surface potential pseudo-equivalent temperature. For the frontogenetic function, the warm and moist air was lifted to the point of saturation, and upstream reignited deep convection in the south of the cold pool. Such backward propagation decreased the moving speed of MCS, and even made it into a quasistatic state. Under the effect of surface mesoscale vortex system, new convective cells organically rotated like vortex, and repeatedly passed Xinxiang, bringing continuous heavy rain to Xinxiang. The moist cold pool was an important source for the surface water vapor. The Taihang Mountain was thought to trap the cold pool from spreading. As a result, the cold pool moved in the opposite direction of the steering flow. Canyon effect of small topography contributed to the south movement of the cold pool. In addition, it provided an important northwest flow for the surface mesoscale vortex system.