Statistical analysis of thunderstorm gust front characteristics in Beijing and surrounding areas

Gust fronts are a key element in the organization of convection initiation, yet comprehensive statistical knowledge of their typical characteristics is still not sufficient. To help alleviate this situation, the Doppler radar data in Beijing and observations of automatic weather stations in Beijing, Hebei, and Tianjin from May to September during 2006—2015 are used to analyze characteristics of gust front cases in Beijing and surrounding areas. Results indicate that 232 out of the 346 gust front cases triggered the formation of thunderstorms. The storm-triggering cases account for 67% of the total. Gust fronts show a strong potential to trigger thunderstorms. The number of days with gust front in June, July, and August accounts for 85% of the total number of days. The gust fronts occur mainly from afternoon to evening (from 12:00 to 21:00 BT), and last for about 0.5 to 3.0 h. Most gust front cases occur to the southeast of Beijing, followed by that to the east and northeast, and the least occur to north, west and northwest. 48% of the parent thunderstorms that produce gust fronts are isolated thunderstorms (including isolated thunderstorms and super-cell storms), 31% are thunderstorm clusters, and 21% are squall lines. 97% of parent thunderstorms have reflectivity above 50 dBz and the gust fronts are characterized on Doppler radar as thin lines of enhanced reflectivity between 10 and 25 dBz. 91% of the gust fronts move with the speed between 10 to 60 km/h. The maximum distance between gust fronts and their parent storms is between 1 and 60 km for 84% of the gust storms. After the parent storms decay with the reflectivity below 30 dBz, 80% of the gust fronts can maintain for no longer than 2 h. Comparing with the eight directions of compass, most of the parent thunderstorms move to the southeast. The relationship between gust front and parent storm moving directions can be classified into seven types: Same, opposite, perpendicular, in obtuse or acute angle, arc diffusion of gust front and stationary parent storm. The type of same moving direction for gust front and parent storm accounts for 32% of the total and is the largest among the above seven types, followed by the types of gust front arc diffusion and stationary parent storm, both of which account for 17% of the total, respectively; the type of opposite moving directions for gust front and parent thunderstorm is the least, which only accounts for 3% of the total. The statistical results show that gust fronts passing by automatic weather stations are often accompanied with increasing wind speed, decreasing temperature, and rising relative humidity and pressure.