Estimating lightning channel characteristics of positive narrow bipolar events using intrachannel current reflection signatures

[1] A set of 133 positive narrow bipolar lightning events located by the Los Alamos Sferic Array (LASA) is examined. The events were selected because their fast electric field change (EFC) records show a secondary positive peak, following the primary positive peak, which is consistent with what would be expected for a propagating current pulse reflecting off an impedance discontinuity along a transmission line. With an assumed propagation speed, the time difference between the primary and secondary (reflected) peak in the field change record offers a direct technique for estimating the length of the discharge channel. If the signal amplitude is assumed to decay exponentially with time and that the reflection coefficient is near unity, the time difference between peaks and the ratio of their amplitudes yields an estimate of the temporal decay rate constant. Statistics on the 133 located events examined show an average peak-to-reflected-peak time of 6.7 mu s, a mean amplitude ratio estimate of 6.1, and an amplitude decay rate constant of 4.0 mu s. Bound by the speed of light, the upper limit on channel length for the typical positive narrow bipolar event (NBE) in this study is shown to be approximately 2 km.