CHARACTERIZATION OF VERTICAL ELECTRIC-FIELDS 500 M AND 30 M FROM TRIGGERED LIGHTNING

Vertical electric field waveforms of leader-return stroke sequences me asured 500 m and 30 m from rocket-triggered lightning are presented. T he 500-m data were recorded during the summer of 1986, the 30-m data d uring the summer of 1991, both at the NASA Kennedy Space Center, Flori da. The 40 leader-return stroke field waveforms at 500 m and the 8 wav eforms 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 r eturn stroke. Only two waveforms at 30 m were suitable for quantitativ e analysis. The widths of the V at half of peak value for these are 1. 8 and 5.0 mu s, while for the 500-m data they are 1 to 2 orders of mag nitude greater, with a median value of 100 mu s. Applying a widely use d and simple leader model to the measured leader electric fields at 50 0 m, we infer, for the bottom kilometer or so of the leader channel, l eader speeds between 2x10(6) and 2x10(7) mis and leader charges per un it length of 0.02x10(3) to 0.08x10(3) C/m. From the two measured leade r electric field changes at 30 m we infer, using the same leader model , for the bottom 100 meters or so of the leader channel, speeds of 3x1 0(7) and 1x10(7) m/s (the corresponding measured waveform half widths are 1.8 mu s and 5.0 mu s) and charges per unit length of 0.14x10(3) a nd 0.02x10(-3) C/m (the corresponding measured leader field changes ar e 81 kV/m and 12 kV/m). The corresponding measured return stroke peak currents for the above two cases are 40 kA and 7 kA, respectively. A p ositive correlation is observed between the magnitude of the leader fi eld change at 500 m and the ensuing return stroke current peak.