Analysis on the mesoscale characteristics of a local rainstorm event under atypical circulation situation in Tianjin

Based on EC reanalyzed data, VDRAS data, and a variety of observations, the mesoscale characteristics of a local rainstorm event under atypical circulation situation happened in Tianjin on 16 August 2014 were discussed. The results are as follows. (1) Before the convection occurred, the easterly transported warm air to Tianjin, which makes the atmospheric moisture contents over Tianjin increased suddenly, providing sufficient water vapor condition for the occurrence of the short time heavy precipitation. (2) There was a divergence airflow at boundary layer on the west side of Tianjin, which led to the formation of dry line.When the frontogenesis disturbance moved eastward, it met with the warm air from the Gulf of Bohai.The disturbance then became stronger, triggering the convection near the area of Tianjin City. (3) When the dry line moved eastward, the gust front interacted moist region in the southeast of Tianjin. Additionally, water vapor transport provided by meso-scale low-level jet stream further enhanced the development of heavy precipitation. (4) The intersection between the cold and warm air masses near surface with the cyclonic shear at low level is a favorable dynamic mechanism for the development of precipitation.