Severity of Lightning Return Strokes: Simulation Study and Review Notes.

The literature on lightning stroke severity indicates that the magnitude of the electric field peak due to the firstreturn- stroke is nearly twice that of the field peak due to the subsequent return stroke. These reports are based on the data collected by lightning detection, and information and field measurement systems. In this paper, field results from the literature are summarised. These are then compared with the results obtained through simulation. Electromagnetic fields generated due to "typical" first (FS) and subsequent (SS) lightning return strokes have been computed using the "Modified Transmission Line with Linear current decay" (MTLL) model. These simulation results are discussed, keeping in view, the field data reported in several recent studies, which compare the severity of first and subsequent-return-strokes. The MTLL based engineering model is adopted to compare the severity of lightning return strokes (FS/SS) as a function of radial distance. The effect of worst-case-ground-conductivity on this ratio is reported. An MTLL model based comparison on emfield FS/SS ratiofor both perfect and worst-case-ground conditions is also reported. These simulation results are compared with those from the "Modified Transmission Line with Exponential current decay" (MTLE) model. In general, the present simulation results not only substantiate the fact that the FS/SS ratio is nearly two times, but also assess a few parameters responsible for low FS/SS ratio (reported in some cases). The present simulation analysis shows that terrain electrical conductivity affects the FS/SS ratio. This may explain the cause for the low FS/SS ratios. [ABSTRACT FROM AUTHOR]