Laboratory simulation of the stepped leader in lightning

It is shown that the 'stepped leader' often observed in lightning discharges is a manifestation of the nonlinear characteristic of the glow surrounding the leader tip, together with the parallel resistance–capacity behaviour of the far-field region. The resulting relaxation oscillations lead to intermittent discharges, which are simulated by adding resistance and capacity to the external circuit of a standard discharge gap experiment.In addition, two complementary experiments were carried out to further illustrate that the stepped leader is subject to a continuous sequence of 'run-stop' conditions, whereby the fast transient displacement current pulse is a manifestation of the 'run' state. A uniform view of the stepped leader and leaders propagating in well-preionized gas, in which displacement current is absent, is presented. This interpretation is largely confirmed by the present experiments as well as those of Gänger and Maier.