Abstract:A squall line is formed in Shandong province,which is influenced by the high trough and surface convergence line in the afternoon 18 August 2012.Based on the automatic weather station data and Jinan Doppler Weather Radar data,this paper studies the merging characteristics of mergence between cell and cell,bow echo and cell during the development of the squall line.Results indicate that:(1) Merging process experiences the primary phase,the intermediate phase and the complete combined phase.The cloud bridge emerges at the middle level of the storm.The echo intensity first decreases and then strengthens during the merging period.(2) The results of the mergence are that the upstream echo decreases and merges with the downstream echo,and provides the abundant water vapor for the downstream echo.The convergence between downdraft outflow and warm moisture air increases the ascending movement of the downstream echo,so the downstream echo develops continuously and replaces the old echo.That is,the mergence belongs to the feeder type.The low level small scale vortexes are strengthened and their base heights reduce because of the mergence,so the meso-scale cyclone or uncorrelated shear is produced.(3) The intensity of two cells weakens during the intermediate merging phase of cell with cell,and strengthens during the complete combined phase.The low vortexes have the characteristics of small scale and strong intensity,the vertical stretching thickness and maximum shear value of the meso-cyclone or uncorrelated shear are larger,and their base heights are lower.The tornado storm expresses characteristics such as long duration,large influenced area and higher intensity,and can cause more serious disasters.(4) The cell maintains development during the entire merging period between the bow echo and cell,while the bow echo decreases in the period of complete combined phase.The low vortexes have larger scale and weaker intensity.(5) The base height,vertical thickness and maximum shear value of the meso-cyclone or uncorrelated shear show high relativity to the intensity of tornado.During the merging process of cells,when the base height or the maximum shear height of the meso-scale cyclone or uncorrelated shear reduces,or the maximum shear value increases abruptly,the tornado would be produced.If the mergence is located in the apex of the bow echo,the tornado would be produced.