The criteria we used to identify the squall lines follow Parker and Johnson (2000). In particular, a contiguous or quasi-contiguous region of 40-dBZ reflectivity extends at least 100 km, exists for at least 3 h, and has a linear or quasi-linear convective area with an apparent common leading edge. Using the criteria, we got 139 squall lines in the three years. Detailed analyses were performed on spatial and temporal distribution, maximum length, maximum intensity, dominant orientation, movement, life span, formation mode, organizational type, and background weather systems etc. Results show that the squall lines have the largest frequency near the boundary between Shandong, Henan and Zhejiang Provinces. The second largest frequency appears in southeast coastal area of China likely associated with landfalling tropical cyclones. All the squall lines occurred from March to October with a peak in July. The diurnal cycle shows a major peak during 18-21 pm (Local time) and a second peak during 03-06 am.
The squall lines have a dominant orientation of southwest-northeast, an eastward motion at 45-55 km/h, length of 200-300 km, maximum intensity of 55-60 dBZ, and a life span of 3-4 h. Most of the squall lines form in a back-building mode, assume a leading-convective-trailing-stratiform organization, and dissipate in a reversed broken-line mode. The environmental weather systems in which these squall lines occur can be categorized into mid-latitude cold front, Meiyu front, and tropical cyclones. Nearly 70% of the squall lines are associated with cold front. The rest 30% are almost equally associated with Meiyu and tropical cyclones. Annual variability of above features has been explored. Furthermore, the radar traits of the squall lines in east China will be compared to their counterparts in a different weather regime such as in the US.
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