Review and Extension of the TCS Model to Consider the Current Reflections at Ground and at the Upper End of the Lightning Channel

This paper gives the overview and review of the traveling current source (TCS) model, which describes the electrical processes during the lightning return stroke. It is shown that the main characteristics of the measured electric and magnetic fields can be reproduced with the TCS model. These are the "initial peak" of the electric and magnetic field for near, intermediate and far distances, the "ramp" (up to the maximum) of the near electric field, the "hump" of the near magnetic field after the initial peak, and the "zero crossing" of the far distant electric and magnetic field. The TCS model is based on the assumption that the lightning current is injected at the top of the increasing return stroke channel represented by a transmission line. The original model is presented and then extended to take into account the current reflections occurring at ground and at the upper end of the return stroke channel. To this end, the ground reflection factor ρ and the top reflection factor R are introduced. Due to the increasing return stroke channel, the top reflection factor is a function of the return stroke velocity. The total current is composed of the source current according to the original TCS model and the reflected currents. An example shows that the ground reflection causes significant variation in the peak values of the channel-base current and of the maximum current derivative. A major effect was also found for the initial peak of the electric and magnetic fields calculated at 3 km distance.