Genesis of return stroke current evolution at the wavefront

•Contributors to the current evolution at the wavefront are identified.•Heating by the high current arc at the wavefront to nascent sections ahead is considered.•Pertinent non-linear transient thermal field is solved using the finite volume method.•It is shown that the thermal field has insignificant contribution to stroke evolution.•Enhancement of electric field is shown to be mainly responsible for stroke evolution.

The channel dynamics at the wavefront is complex and is primarily responsible for the evolution of return stroke current. The enhancement of channel conductance at the wavefront is necessary for the evolution of current and hence, return stroke. In this regard several questions arise like: (i) what causes the enhancement of conductance, (ii) as the channel core temperature and electrical conductance are closely related, does one support the other and (iii) is the increase in core temperature on the nascent section of the channel the result of free burning arc of the wavefront just below. The present work investigates on these issues with appropriate transient thermal analysis and a macroscopic physical model for the lightning return stroke. Results clearly indicate that the contribution from the thermal field of the wavefront region to the adjacent nascent channel section is negligible as compared to the field enhancement brought in by the same. In other words, the whole process of return stroke evolution is dependent on the local heat generation at the nascent section caused by the enhancement of electric field due to the arrival of the wavefront.