Reproducing the Fine Structure of LEMP Using 3-D Lightning Observations

The lightning electromagnetic pulse (LEMP) often exhibits one or more subsidiary peaks or undulations, also termed fine structure. In order to investigate the relationship between LEMP fine structure and return stroke (RS) channel parameters, a comprehensive observation, including LEMP measurement, thunder imaging and VHF mapping, is conducted. The 3D channel geometry and velocity could be derived by observation results. Thereafter, a piecewise linear RS model is proposed, which make use of the observed channel parameters combined with an engineering return-stroke model. The comparison between the observed LEMP and model predicted magnetic field waveforms are in well agreement with each other, especially for the initial several tens of microseconds, which demonstrate that the channel geometry and velocity dominate the initial fine structure. The major difference in the decaying stage may result from the variation of other channel parameter, such as variation of current amplitude, velocity, and risetime with height.