The Mechanism of the Lightning Discharge

The leader stroke mechanism for the lightning discharge is explained on the basis of ion recombination in the discharge channel. It is assumed that a pilot streamer advances continuously from cloud to ground at a speed of 2 × ${10}^7$ cm per sec. The current which flows into the tip of the pilot streamer is calculated as 0.1 amp., and it is considered that this current must be maintained at an approximately constant value for the pilot streamer to propagate. The resistance of the channel which joins the pilot streamer to the cloud is then calculated in terms of the ion density, and it is shown that the voltage gradient increases sufficiently to cause successive breakdown of the channel to occur at intervals of some 50 microseconds, i.e., the stepped leader stroke. The high speed of step and dart leaders is explained by the fact that the ion density ahead of their tips is about ${10}^{10}$ and ${10}^7$ per ${\mathrm{cm}}^3$, respectively.