Spatiotemporal distributions and environmental characteristics of three types of regional severe convective weather processes associated with the Northeast China cold vortex

Northeast China cold vortex is one of the important synoptic-scale systems that causes severe convective weather in the warm season in China. In order to compare and analyze the spatiotemporal relationship between Northeast China cold vortex system and different types of severe convective weather processes and their environmental characteristics, based on the Fifth Generation Atmospheric Reanalysis Product of European Centre for Medium-Range Weather Forecasts and hourly precipitation and wind data provided by the National Meteorological Information Centre of China, severe convective weather processes including nine thunderstorm wind gust, nine heavy precipitation and eight hybrid type processes associated with Northeast China cold vortex from April to September of 2017—2021 are screened out. Comparative analysis is carried out by dynamic synthesis approach. The results are as follows: (1) Differences in the spatiotemporal distribution of the three types of severe weather processes and Northeast China cold vortex system are significant. In the thunderstorm wind gust processes, more than 70% of thunderstorm wind gusts occur in the southwest or south of the cold vortex center. However, in the hybrid type processes, more than 70% of thunderstorm wind gusts occur in the southeast or south of the cold vortex center. More than 75% of the heavy precipitation events occur in the south to southeast of the cold vortex center in both the hybrid type processes and heavy precipitation processes, but a higher proportion of the latter occur in the southeast of the cold vortex. Processes of thunderstorm wind gust and heavy precipitation mainly occur in the development and maturity stages of the Northeast China cold vortex, while hybrid processes mainly occur in the maturity stage. (2) The characteristics of circulation patterns and environmental conditions of the three types of severe weather processes are significantly different. Thunderstorm wind gust processes are concentrated from May to June, generally corresponding to a stronger cold vortex, denser 500 hPa isotherms, a drier atmosphere, a larger vertical temperature lapse rate and stronger vertical wind shear. Thunderstorm wind gusts mostly occur near the front area. The cold and dry advection in the middle troposphere superimposing on the shallow warm and wet air in the lower layer is conducive to the growth of unstable stratification in the frontal zone. Meanwhile, the downdraft formed by evaporation and cooling of precipitation particles couples with the convergence in the frontal zone, leading to the formation of regional surface wind gusts. Heavy precipitation processes are concentrated from July to August, corresponding to a weaker cold vortex and sparsely distributed isotherms. Heavy precipitation generally occurs in the region of strong unstable stratification near the warm sector ahead of the front, which corresponds to an environment with more water vapor content, smaller temperature differences between middle and low layers and weaker vertical wind shear. The time period and cold vortex intensity corresponding to the hybrid type processes are closer to that of the heavy precipitation processes, and the conditions of water vapor, vertical temperature lapse rate and vertical wind shear are between those for the above two types of processes, but DCAPE is the largest in the three types of processes. However, compared with the environmental characteristics of thunderstorm wind gusts and short-term heavy precipitation in the middle and low altitudes of China, the three types of severe weather processes under the background of the Northeast China cold vortex correspond to stronger deep vertical wind shear condition, indicating that the cold vortex system provides strong synoptic scale dynamic forcing.