Abstract:By using the NCEP analysis data, Doppler radar observation data, conventional meteorological observation data and the numerical simulation results, the evolution and causes of rear inflow during a squall line, occurred in North China and Liaoning area on July 30, 2016, have been investigated. The investigation shows that squall line occurred in front of the trough line of mid-latitude new Northeast cold vortex, where lower layer has water vapor convergence and wind convergence line on surface, which is accompanied by strong convection effective potential energy release. There is meso-a-scale westerly wind belt in the middle of the back of the squall line (and behind of trough of Northeast cold vortex), which results in the opposite horizontal vorticity and trumpet circulation structure in the vertical direction. The negative vorticity of horizontal vorticity in the middle-lower layers, which is favorable for the formation of the sinking motion, leading to the real inflow and strong wind zone in the lower layer, which formats and develops the squall line; meanwhile, the positive vorticity of horizontal vorticity of middle-upper layers is favorable to the ascending movement. The structure is different from the classical squall line structure. In the middle of squall line rear edge, there is a strong wind speed area with the development of the squall line. The formation of the strong wind speed area is connection with the convection strength and non-thermal wind vorticity. When convection develops strongly, there are negative non-thermal wind vorticity in the lower layer and positive in higher layer, which results in the rear westerly acceleration in middle layer and deceleration in lower layer and is favorable for the strengthening of rear inflow and convergence of airflow in front of convection system. On the contrary, when the convection is weakened, so do the non-thermal vorticity and rear inflow. The conceptual module of formation and evolution of rear inflow has been analyzed in paper.