Analysis of the VHF-UHF electromagnetic radiation of lightning: Application to a model of the negative stepped leader propagation

The space and time characteristics of the VHF-UHF radiation from lightning are analyzed on the bases of 300 MHz emission sources, localized in three dimensions by interferometric measurements. The main phases that contribute to the development of intracloud lightning are examined in detail, also using electric field measurements at the lower frequency. This research is complemented by an experimental and theoretical analysis of long discharge (8m) radio emissions generated with both polarities in the laboratory. These investigations revealed that the VHF radiation is associated with the channel reillumination phase accompanying each step in the negative spark. The outcome of this work is the creation of a simple model for the propagation of the negative leader. The current and the radiated field during this phase of the discharge are computed from an equivalent electric circuit using the physical laws governing the variation of resistance. The extrapolation of these results to the case of the stepped leader of natural lightning is discussed.