Wavelet-based multifractal analysis of the radiation field of first return stroke in cloud-to-ground discharge
基于小波的地闪首次回击辐射场的多重分形分析

By using electric field change data obtained during the summer of 2002 in Qinghai province,we analyze the detection of the radiation field of first return stroke involved in negative cloud-to-ground lightning discharges and its multifractal behavior with the Wavelet Transform Modulus Maxima(WTMM) method.We find that the variation of wavelet coefficients at the lower level of decomposition exhibit a sharp peak just at the position of the main pulse peak of return stroke(return stroke point),thus the return stoke points can be reliably and effectively detected.We also find that the radiation field of first return stroke exhibits strong multifractality,and all scaling behavior can be fitted with a modified version of the binomial multiplicative cascade multifractal model.The two characteristic parameters,the mean width of spectrum and the minimum spectrum exponent,are 1.5 and-0.11 respectively.We suggest that the wavelet and multifractal method is a powerful tool for detection and reorganization of lightning signals.