The Electric Field Intensity and Its Systematic Changes Under an Active Thunderstorm

Abstract

Reliable induction electric field intensity meters were installed at the four corners of an 8.5 kilometer square. The values of the field intensity were transferred to a base laboratory via telephone lines and applied to a 4 channel oscilograph permitting the simultaneous recording of some 480 lightning discharge events occurring in a single typical active thunderstorm. Two other channels measured the current discharged by a sharp point and the charges on individual raindrops falling at the base laboratory. Negative charges normally accumulated overhead and were transferred out of the clouds in 95% of the lightning discharges. The average electric field at the ground prior to discharge was +21.8 volts cm?1 volts cm100 These values were notably smaller than those measured in 1955 on the Ransas plains. Curves are given for the average initial and final values of the electric field, for the average departures at each station from the network average and for the time varying positions of the approximate centers of free electrical charge. The frequent complete reversal of the normal initial electric field intensity by the lightning discharge is confirmed. The relation of the large negative post-lightning fields to the reverse currents and corona discharge backward through the original discharge channels or branches is considered. It is noted that the negative corona is much larger and more easily visible than the positive corona under the same conditions of voltage and current. Accordingly, frequent reports of post-lightning electrical phenomena are to be anticipated.