In order to evaluate the influence of return stroke current on lightning electromagnetic field associated with tortuous lightning channel

a model of lightning electromagnetic field for a tortuous lightning channel is proposed based on the dipole method.Lightning electromagnetic fields in far-zone generated by different channel currents are calculated.Then the influences of azimuth angle

rise time and half-value time of return stroke current on the multifractal characteristics of lightning electromagnetic field are obtained by using multifractal analysis.The results show that the width Δα and asymmetry factor B of multifractal spectrum for lightning electromagnetic field in far-zone are more susceptible to the azimuth angle and return stroke current waveform than the exponent 0α.The longer of the rise time of return stroke current is

the more smooth the lightning electromagnetic field waveform in far-zone will be.Correspondingly

the exponent 0α and width Δα of multifractal spectrum decrease with the increasing of rise time

and the asymmetry factor B increases with the increasing of rise time.The longer the half-value time of return stroke current is

the smaller the exponent 0α and width Δα of multifractal spectrum for lightning electromagnetic field in far-zone will be.Moreover

the asymmetry factor B decreases and subsequently increases with the increasing of the half-value time.