关键词: 飑线过程, 雷暴大风, 红外、水汽及可见光云图

Abstract: Based on the infrared and water vapor cloud images of Himawari-8 satellite, the visible cloud images of FY-2E satellite, the composite reflectivity factor mosaic maps of Doppler radar, the observation data of conventional weather stations and automatic weather stations and radionsonde data, the cloud image characteristics and maintaining mechanism of the squall line process in Shanxi Province on 21 September 2017 were analyzed. The results are as follows: (1) The squall line weather process was caused by the large-scale Mongolia cold vortex weather system. The surface cold front moved eastward to the unstable potential area, which triggered the formation of the squall line system. The transformation of system configuration structure in high and low level of troposphere and the formation of mesoscale cyclone and convergence line from the outflow cold air of surface mesoscale high pressure and environmental wind field were the development and maintenance mechanisms of the squall line. The convective cloud clusters merged and developed between the surface cold front and 850 hPa shear line, and the development of surface mesoscale high and low pressure increased the pressure gradient, which led to the enhancement of the squall line, and further caused surface gale during the passage of the squall line. (2) At the initial stage, the squall line was formed in the large gradient area behind the low cloud-top brightness temperature region, the rough texture area of cloud-top, the wet side of the dry and wet boundary, and the position of cold cloud cover slightly moved in front of the squall line. At the development stage, the echo of the squall line strengthened in low cloud-top brightness temperature region, and it moved along the moving direction of the low value center of brightness temperature. At the mature stage, the radar echo of the squall line coincided with the low value region of cloud-top brightness temperature. (3) The arcus cloud line, the up rushing cloud-top and the shadows on one side of convective cloud belt were the early signs of the development and enhancement of convective cloud clusters.

Key words: squall line process, thunderstorm gale, infrared, visible and water vapor cloud image