Measured fields and earth potentials at 10 and 20 meters from the base of triggered lightning channels

摘要

Vertical electric fields, azimuthal magnetic fields, and earth voltages developed over a 0.5-m radial step distance have been measured at 10 and 20 m from the ground attachment point of triggered lightning. The magnetic fields are found to follow Ampere's law closely, in both amplitude and waveform. The relationship between maximum vertical electric field change due to a descending dart leader and the peak of its associated return-stroke current is linear. Recorded earth step voltages have the same waveforms as the incident return-stroke currents and, for distances between 10 and 20 m from the strike point, their amplitudes exhibit a 1/r dependence. Statistics are given on the observed occurrence of radial surface ground arcs emanating from the earth attachment point as a function of peak incident return-stroke current.