云闪放电通道发展及其辐射特征

Propagation of the Lightning Channel and Electromagnetic Radiation in IC Flashes

利用闪电宽带干涉仪系统,对中国南方(广东)地区云闪时空演变特征、辐射及其相应电场变化特征进行分析研究。根据云闪电场变化波形,云闪放电过程可划分成活跃阶段和最后阶段,辐射源定位结果表明,云闪放电起始于向上发展的负击穿过程,通道向上发展的速度约为3～3.3×105m·s-1。云闪放电的主通道在活跃阶段形成,该期间辐射源随时间演变和相应电场变化表明,云内电荷结构具有上正下负的偶极性电荷结构。云闪的最后阶段辐射源主要在早期形成的通道内出现,其辐射源活动特征与地闪的回击过程比较相似;云闪辐射能量主要集中在2～3MHz以下的低频段,且辐射强度随频率增加迅速减弱。

Radio frequency observations of intracloud (IC) lightning were made in Guangdong of China in 1999, with the broadband lightning interferometer. The spatial and temporal variations of radiation sources, the spectra and associated electric field change have been analyzed in this paper.The intracloud discharge could be divided into both the active and finally stages according to the waveforms of the intracloud lightning. The locations of the radiation sources indicate that the intracloud lightning is initiated usually by a negative breakdown processes upwards, and the upwards propagation speed of the lightning channel is about 3～3.3×105m·s\+\{-1\}. The main channel of the intracloud discharge is formed during its active stage. The characteristics of the spatial and temporal variations of radiation sources and the electric field change caused by lightning discharge indicate that the primary charge in thunderstorm has a distribution of positive electricaldipole. During the finally stage of the intracloud, the radiation sources appear mainly in thepreviously formed channel and is similar to the characteristics of the radiation sources in return stroke of the cloud\|to\|ground lightning. The spectra radiated by lightning discharged have peaks in the frequency interval from 2 to 3 MHz and the intensity of radiation reduce with the frequency.