Lightning-induced currents in a buried loop conductor and a grounded vertical conductor

Currents in (1) a 100 m by 30 m buried rectangular loop conductor (counterpoise) and (2) a grounded vertical conductor of 7 m height induced by natural and rocket-triggered lightning at distances ranging from 60 to 300 m were recorded in 2005 at the International Center for Lightning Research and Testing (ICLRT). The peak values of 12 triggered lightning channel-base currents and the peak values of the induced currents in the counterpoise are strongly correlated. The first few microseconds of the current induced in the vertical conductor by triggered lightning return strokes 100 m away resemble electric field time derivative waveforms simultaneously measured at the ICLRT. During a close natural lightning flash, five pre-first return stroke current pulses with peak currents up to 140 A were measured in the vertical conductor. These are apparently associated with multiple attempts of an upwarddirected unconnected leader in response to the charge lowered by downward-propagating leader steps.