Analysis Of The Squall Line Process In The Beijing-Tianjin-Hebei Region Under The Background Of Cold Vortex

In the cold vortex background of the Beijing-Tianjin-Hebei region,the squall line process and the strong convective weather forecast are difficult.In this paper,the conventional and unconventional data are used to analyze the 36 squall lines in the Beijing-Tianjin-Hebei region under the cold vortex background for nearly ten years.The case analysis of the squall line in the cold vortex weakening stage is beneficial to enhance the understanding of such squall line process and improve the forecasting ability of strong convective weather in the cold vortex background.The study found that:(1)In the cold vortex background,the squall line in the Beijing-Tianjin-Hebei region mainly occurs in the summer of June and July,and it is generated in the afternoon to the evening.It matures at night and ends in the middle of the night.The life history is mostly 3 to 4 hours.There is a long-life history process.The location of the formation is concentrated at the junction of Beijing-Tianjin border and mountain plains,and then matures in the plain,ending at the eastern coast,moving from northwest to southeast,with a speed of about 8~14m/s,and the formation of the squall line is mostly BL type.Most of the dissipation methods are RBL type,and the organization mode is mostly TS type.(2)Most of the squall line occurs in the stage of generation and enhancement of the cold vortex,which occurs in the weakening stage of the cold vortex.The squall line is located in the south-south or south-south direction of the cold vortex,about 1000 km away from the center of the cold vortex,and the cold vortex passes through the peripheral accompanying system and The activity of cold air affects the occurrence of the squall line in the Beijing-Tianjin-Hebei region.(3)Under the favorable large-scale conditions,the squall line will be generated in the cold vortex weakening stage,the unstable stratification,the sufficient water vapor condition will make the squall line develop strong,the bow echo will appear,and the low-level ground convergence line will trigger the initial convection.The convection is organized into a squall line,and the high-altitude guided airflow and the vertical wind shear dominate the squall line movement,and the development is strengthened under the favorable splicing conditions and the cooperation of water vapor.