Analysis of Squall Lines Under the Background of Cold Vortex
Cold vortex is identified based on the definition of cold vortex, and 73 cold vertexes during 2008-2013 are identified. According to the screening criteria of squall line, the qualified squall lines are screened out. Digital radar mosaics of composite radar reflectivity are used in this study to perform the survey. Detailed analyses are carried out on the spatiotemporal distribution, moving characteristics, formation, dissipating way of squall lines and the relationship between cold vortex and squall lines. The results show that (1) 73 cold vortexes and 17 squall lines during 2008-2013 are identified, which mainly formed in Huaihe River Basin, North China and Northeast China. (2) Squall lines have obvious features of monthly and diurnal variations, with nearly 58.8% in July, and 52.9% from afternoon to evening. (3) Squall lines form mainly in the south of the cold vortex. During the different stages of cold vortex, squall line develop in different positions. (4) Some squall lines move towards eastsouth influenced by the midlatitude westerlies weather system, and others move from northwest to southeast. Due to the influence of the cold vortex system, squall lines move fast. (5) Most squall lines under the background of cold vertex are accompanied by heavy rainfall. The main forming mode is embedded areal (EA), the main dissipation mode is reversed broken areal (RBA), and EA type squall lines are often seen in highly humid environment.