A squall line with a long life is very likely to cause a wide range of catastrophic gale weather. The study of its structure and

maintenance mechanism is of great reference significance to the forecast of catastrophic gale weather. The rear inflow of a warm zone squall line that caused strong gale in Jiangnan area on March 4, 2018 was analyzed by using the ground observations, radar data, NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) FNL (Final Operational Global Analysis) reanalysis and high-resolution model simulation results, and the maintenance mechanism of the squall line was discussed. The results show that the squall line occurred in a warm environment in front of the south branch trough with the same southwesterly airflow in upper and lower layers. The environment was characterized by moderate to strong vertical shear of 0–6 km, high convective effective potential energy, and obvious dry areas in the middle layer and near the surface. The 3 h negative barotropic anomaly index has

a good indication in this process. The squall line showed a “TS” structure, but the stratus area was relatively narrow. The reflectivity factor kernel was located in the downdraft below the mid-level radial convergence. The results of the model simulation show that the rear inflow and downdraft forced counterclockwise and clockwise vertical circulation in the interior and rear of the system, respectively, which constituted the most important structural characteristics of the squall line. The rear inflow was close to the rear edge of the system and located in the middle troposphere, which caused the updraft to change from inclined to vertical direction. After that, the rear inflow moved away from the system and merged with the lower outflow to continuously lift the warm and moist air. The synergistic effect of the rear inflow and the front inflow made the squall line maintain for a longer time.