Tentative analysis of a continuous local heavy rainfall event over Tianjin on 25 July 2012

Tentative analysis of a continuous local heavy rainfall event from July 25 to 26 in 2012 over Tianjin is performed with the conventional and automatic weather stations (AWS) observation data, NCEP 1°×1° reanalysis data, FY-2E satellite imageries, Doppler radar data and data from a mesoscale numerical model. The results show that this event occurs against the background of stable meridional circulation and typical“two troughs and one ridge”pattern in the mid-and high- latitudes. Vicente typhoon low in South China and southerly jet in the western part of subtropical high form a crucial water vapor and energy transfer to North China jointly, thus, abundant moisture from Bengal Bay is continuously transported to heavy rain areas in North China. The southwest warm and wet airflow at the edge of subtropical high is conveyed northwards to form high temperature and high humidity environment over the North China Plain to accumulate unstable energy producing the extra heavy rain. Meanwhile, the intrusion of cold air strengthens vertical upward motion, and the meet of cold and warm air triggers local energy release reinforcing precipitation quickly. The development and reinforcement of three β-mesoscale convective cloud clusters incoherence with several γ-mesoscale convective echoes result in the severe precipitation, and remarkable train effect and rich water vapor supply lead to high intensity and long lifetime of the rainstorm.