0.1~40 MHz地闪、 云闪及NBE事件的辐射场频谱特征分析

利用宽带傅立叶分析法对2008年7月30日和8月4日两次雷暴过程中， 距离观测点5~20 km范围内的55次负地闪回击过程， 33次云内闪电过程以及20次双极性窄脉冲事件（NBE）的电磁辐射信号进行了观测分析， 得到地闪回击、 云闪放电初始阶段以及双极性窄脉冲事件在0.1~40 MHz频带宽度下的电磁辐射能量谱密度。结果表明, 这三类闪电放电过程的辐射频谱波形均呈现出随频率增加、 幅值减小的趋势， 但在辐射强度和衰减速率上存在一定的差异。负地闪回击幅频波形在6~28 MHz频段上衰减速率相对缓慢； 云闪初始阶段在全频带上始终遵循f-1.2~f-1.4之间的衰减率递减， 且其频谱幅值与地闪回击的辐射能量谱幅值相差不大； NBE事件在0.1~40 MHz频带中辐射能量谱幅值基本都明显大于其他两类闪电放电过程， 特别是在10 MHz以上的HF、 VHF频带上其差异可达到20 dB。

The Lightning Radiation Field Spectra of Cloud-to-Ground,Intra-Cloud Flashes and Narrow Bipolar Events in the Intervals of 0.1 to 40 MHz

The broadband radio frequency(RF) observations of cloud-to-ground(CG), intra-cloud(IC) flashes and narrow bipolar events (NBE) at "Guangzhou Field Experiment Site for Lightning Research and Testing" during the summer of 2008 were conducted. The electromagnetic radiation produced by negative CG return strokes, initial discharge of IC flashes and NBEs have been analyzed using the Fourier method to obtain amplitude spectra for frequencies from 0.1 to 40 MHz. The results indicate that the spectral amplitude of all the three kinds of lightning discharges decrease in different rates with the frequency increasing. The spectral of the negative CG return strokes has a slow decreasing rate as f~(-0.8) between 6 MHz and 28 MHz; while the spectral of the initial discharge of IC flashes has a consistence decreasing with rate of f~(-1.2) to f~(-1.4) and the spectra amplitude tends to be similar to that of the return strokes. The spectrum of the NBEs shows a higher radiation energy over the entire frequency interval, especially above 10 MHz, being 20 dB higher than that of other discharges.