On the computation of electric fields from a lightning discharge in time domain

Two different approaches to the computation of electric fields from the lightning return stroke in the time domain are compared and discussed. These approaches are the dipole technique and the monopole technique. The lightning channel is modeled as a linear antenna. It is shown analytically, for the case of an arbitrary source distribution on the antenna, that both these techniques yield the same total fields and the same Poynting vectors and therefore are equivalent. However, the expressions for the individual field components in the time domain for these techniques, traditionally identified by their distance dependence as electrostatic, induction and radiation terms, are different. The differences between the corresponding field components are considerable at close ranges, but become negligible at far ranges.