Approximation characteristic between LEMP on earth surface and channel-base current

Based on the dipole technique, the exact expressions and approximate expressions for LEMP on earth surface are derived from the TL model and specified channel-base current described by a pulse function. According to the comparisons between the exact results and approximate results, the waveforms of LEMP and its derivative are similar to the lightning channel-base current and its derivative, respectively. In near-field, the electric field and its derivative waveforms of the approximate results are essentially coincident with the corresponding waveforms of the exact results within 100 m. The magnetic field waveforms of approximate results are essentially coincident with the waveforms of the exact results within 500 m, and the magnetic field derivative waveforms of the approximate results are essentially coincident with the waveforms of the exact results within 200 m. In far-field, the waveforms of the approximate results are essentially coincident with the waveforms of the exact results in the rising edge before the initial peak value. At the distance beyond 100 km, the waveforms of the radiation field component and the scaled channel-base current appear identical. The difference between the derivative waveforms of the LEMP field and the scaled channel-base current in the first three microseconds is slight and can be ignored.