Lightning as an asymmetric branching network

The polarity asymmetry in lightning macroscopic behavior is well established for both cloud-to-ground and intracloud flashes. Negative polarity discharges to the ground most often consist of a series of strikes passing through one channel, while positive flashes, as a rule, are limited to one stroke; negative and positive leaders of lightning discharges have significant morphological differences; the growth of positive leaders is accompanied by the development of negative recoil leaders, and positive recoil leaders have never been observed (or do not exist). At present a consistent description of the mechanisms of macro-scale manifestations of the lightning discharge asymmetry causes considerable difficulties. Here we use the hierarchical Horton - Strahler scheme to estimate the structural asymmetry of the lightning discharge tree on the analogy with river systems. We postulate that displacement of the bi-directional leader reversing point (zero charge level of the lightning channel corona sheath) from the place of initiation towards the positive leader development is a fundamental manifestation of the lightning polarity asymmetry. This approach not only has the potential to relate the reversing point displacement rate with the difference in peripheral currents, but also helps uncover the mechanism that provide both the competitive suppression of the positive leader side branches and the negative leader renewal. Our results further indicate that the reversing point displacement determines the lightning principal direction of propagation. Lightning structural asymmetry is estimated using Horton - Strahler numbers Lightning reversing point moves towards the positive leader tip The difference in lightning peripheral currents determines reversing point rate Asymmetry provides competitive suppression of the positive leader side branches.