Computation of the diameter of a lightning return stroke

The diameter of lightning return strokes has been measured by a number of different methods, with little consistency in the results. In this research, the diameter of the return stroke is computed according to simple electrical circuit models based on other experimental results. The computed diameters for different situations may help to clear up the discrepancies between the experimental diameter measurements. Two models are considered. The first is a lumped, resonant circuit; the second is a charged transmission line. Both models give current waveforms that closely approximate the current actually measured at the base of lightning strokes. In both cases, the diameter computed is the same. The diameter of a first return stroke is found to lie in the range 1–4 cm. Subsequent return strokes are smaller, with diameters in the range 0.2–0.5 cm. In many cases, strokes to towers have shown evidence of the smaller strokes occurring alone. These are explained as strokes initiated by an upward leader.