北京及周边地区雷暴阵风锋特征统计分析

为全面和系统研究北京及周边地区阵风锋各方面特征，使用2006—2015年暖季（5—9月）北京多普勒雷达探测资料及北京、河北、天津自动气象站观测资料对北京及周边地区的阵风锋过程进行综合统计分析。结果表明，346次阵风锋过程有232次触发了对流，占总数的67%，表明阵风锋对雷暴具有较强的抬升触发能力。阵风锋在6—8月出现的日数占5—9月阵风锋总日数的85%；出现的时段主要是午后至傍晚（12—21时，北京时），维持时间0.5—3 h；阵风锋在北京东南方向生成的数量最多，且触发对流的次数也最多；其次为偏东和东北方向；偏南和西南方向生成阵风锋数量居中，而偏北、偏西和西北地区阵风锋个例相对较少，触发对流的比例也相对较低。产生阵风锋的母风暴中48%为孤立雷暴（包括孤立多单体和超级单体风暴），31%为雷暴群，21%为飑线；97%的母风暴最强回波在50 dBz以上，阵风锋的回波强度为10—25 dBz。91%的阵风锋移动速度集中在10—60 km/h，84%的阵风锋与母风暴的最大距离为1—60 km；在母风暴回波强度减弱到30 dBz以下时，80%的阵风锋能够继续维持的时间不超过2 h。阵风锋母风暴向东南方向移动的个例最多，从阵风锋和母风暴移动方向的关系来看，阵风锋与母风暴移向一致的情况占比最高，为32%，其次为母风暴无移动及阵风锋弧形扩散情况，各占17%；阵风锋与母风暴移向相反情况所占比例最低，只有3%。最后统计了阵风锋经过地面自动气象站时，自动观测量的变化情况。结果显示，阵风锋在经过地面自动气象站时会造成风速增大、温度降低、相对湿度增大、气压升高。 

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.