Characterization of vertical electric fields 500 m and 30 m from triggered lightning

Vertical electric field waveforms of leader-return stroke sequences measured 500 m and 30 m from rocket-triggered lightning are presented. The 500-m data were recorded during the boreal summer of 1986, the 30-m data during the summer of 1991, both at the NASA Kennedy Space Center, Florida. The 40 leader-return stroke field waveforms at 500 m and the 8 waveforms at 30 m all appear as asymmetrical V-shaped pulses, the bottom of the V being associated with the transition from the leader to the return stroke. Applying a widely used and simple leader model to the measured leader electric fields at 500 m, the authors infer, for the bottom km or so of the leader channel, leader speeds between 2×106 and 2×107 m/s and leader charges per unit length of 0.02×10-3 to 0.08×10-3 C/m. From two measured leader electric field changes at 30 m the authors infer, using the same leader model, for the bottom 100 m or so of the leader channel, speeds of 3×107 and 1×107 m/s and charges per unit length of 0.14×10-3 and 0.02×10-3 C/m, respectively. The corresponding measured return stroke peak currents for the above two cases are 40 kA and 7 kA, respectively. A positive correlation is observed between the magnitude of the leader field change at 500 m and the ensuing return stroke current peak