北京地区的闪电时空分布特征及不同强度雷暴的贡献

利用北京闪电定位网(BLNET,Beijing Lightning Network)和SAFIR3000(Surveillance et Alerte Foudre par Interometrie Radioelectrique)定位网7年共423次雷暴的闪电资料,并按照雷暴产生闪电多少,同时参考雷达回波和雷暴持续时间,将雷暴划分为弱雷暴(≤1000次)、强雷暴(>1000次且≤10000次)和超强雷暴(>10000次),分析了北京地区的闪电时空分布特征及不同强度等级雷暴对闪电分布的贡献。北京总闪电密度最大值约为15.4 flashes km-2a(^-1),平均值约为1.9 flashes km^-2a(^-1),大于8 flashes km^-2a(^-1)的闪电密度高值区基本分布在海拔高度200 m等高线以下的平原地带。不同强度雷暴对总雷暴闪电总量贡献不同,弱雷暴(超强雷暴)次数多(少),产生的闪电少(多),超强雷暴和强雷暴产生的闪电分别占总雷暴闪电的37%和56%。不同强度雷暴对总雷暴的闪电密度高值中心分布和闪电日变化特征影响显著,昌平区东部、顺义区中东部和北京主城区是总雷暴闪电密度大于12 flashes km-2a(-1)的三个主要高值区中心,前两个高值中心受强雷暴影响大,而主城区高值中心主要受超强雷暴影响。总雷暴晚上频繁的闪电活动主要受超强雷暴和强雷暴影响,这两类雷暴晚上闪电活动活跃,分别占各自总闪电的69%和65%,而弱雷暴闪电活动白天陡增很快,对总雷暴午后的闪电活动影响大。另外,不同下垫面条件闪电日变化差异大,山区最强的闪电活动出现在白天,午后闪电活动增强很快,主峰值出现在北京时间18:00,而平原最强的闪电活动发生在晚上,平原(山麓)的主峰值比山区推迟了约1.5小时(1小时)。

Spatial and Temporal Distribution of Lightning Activity and Contribution of Thunderstorms with Different Lightning-Producing Capabilities in Beijing Metropolitan Region

Based on the lightning data from BLNET (Beijing Lightning Network) and SAFIR3000 (Surveillance et Alerte Foudre par Interometrie Radioelectrique), the spatial and temporal distribution characteristics of lightning flashes produced in 423 thunderstorms in Beijing in seven years are analyzed. According to number of lightning flashes generated by a thunderstorm, and reference both radar echo and thunderstorm duration, the 423 thunderstorms are divided into three categories: weak thunderstorm (≤1000 times), strong thunderstorms (1000 to 10000 times), and super thunderstorms (>10000 times). The contribution of each thunderstorm category to the total lightning flash distribution is analyzed. The average lightning flash density in Beijing is about 1.9 flashes km-2 a-1, and the maximum is about 15.4 flashes km-2 a-1, in the southeastern plan region. The area of high lightning flash density greater than 8 flashes km-2 a-1 is basically distributed in the plain area with altitude below 200 m. Thunderstorms of different intensities contribute differently to the total thunderstorm lightning flashes. The weak thunderstorms are more in number but produce fewer lightning flashes, while the super thunderstorms are fewer but produce more lightning flashes. The lightning flashes generated by super thunderstorms and strong thunderstorms account for 37% and 56% of the total thunderstorm lightning flashes, respectively. Thunderstorms of different intensities have a significant effect on the distribution of high-density lightning flash centers and the characteristics of daily changes in lightning flash. The eastern part of Changping District, the central and eastern parts of Shunyi District, and the main urban area of Beijing are the three high-flash-density regions with a density value greater than 12 flashes km-2 a-1. The first two high-value centers are greatly affected by the strong thunderstorms, while the high-value center in the urban areas is mainly affected by the super thunderstorms. The frequent lightning activities in the evenings are mainly caused by the super thunderstorms and strong thunderstorms. These two types of thunderstorms are active at night, accounting for 69% and 65% of the total lightning flashes, respectively. The weak thunderstorm lightning activity increases rapidly during the day and contributes greatly to the afternoon lightning activity of the total thunderstorm. In addition, the diurnal variation of lightning activity under different underlying surface conditions varies widely. The lightning activity is more likely to occur during the daytime in the mountainous area, and it increases rapidly in the afternoon, with the main peak appearing at 1800 Beijing time. However, the peak lightning activity in the plain occurs at evenings. The main peaks of the plain and hill regions are delayed by about 1.5 h and 1 h compared with the peak of the mountainous area, respectively.