Multiscale analysis of lightning return stroke
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摘要: 利用聚合经验模式分解(EEMD)方法对闪电负地闪回击电场波形进行了分析并得到一系列具有物理意义的内禀模态函数 (IMF)。 结果表明，IMF1是高频噪声项,趋势项R主要是静电场作用的结果。 IMF2~IMF11表现出闪电通道的不同尺度放电特征。通过计算IMF分形维数，发现越高阶的IMF对应着越大的分形维数，表明越高阶的IMF对应着越曲折的闪电放电通道。相比于基于经验模式分解（EMD）的希尔伯特-黄变换（HHT）谱和小波谱，基于EEMD的HHT谱能改善模态混叠现象,EEMD更适合于观察像闪电这种非平稳非线性信号。Abstract: Ensemble empirical mode decomposition (EEMD) of the lightning negative return strokes was conducted and a set of almost complete and orthogonal components named intrinsic mode functions (IMFs) having physical meaning were obtained. The results show that IMF1 is the high frequency noise item and the residual item is mainly due to the electrostatic field. IMF2-IMF11 represent the discharge characteristics of the lightning channel in different scales, respectively. According to the calculation of the fractal dimension of different IMFs, the fractal dimension will increase with the increasing IMF order, indicating that the IMF with higher order corresponds to the discharge channel with increasing tortuosity. It is also found that EEMD-based Hilbert-Huang transform (HHT) spectrum can ameliorate mode mixing and it is more suitable for analyzing the lightning than EMD-based HHT analysis and wavelet analysis.
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