Quantitative study of strokes and continuing currents in lightning discharges to ground

Abstract

Results of measurements and calculations of the charge brought to earth by individual strokes and continuing currents from lightning flashes in New Mexico thunderstorms are presented. Hybrid flashes, which contain at least one long-continuing current interval, lower approximately twice as much charge as do the discrete flashes. The average value of negative charge lowered to earth in hybrid flashes is 34 coulombs compared with 19 coulombs for the discrete flashes, a difference accounted for by the presence of the long-continuing (>40 msec) current intervals of average duration 150 msec, during which time an average charge of 12 coulombs is lowered to earth. The continuing currents vary over a relatively narrow range from a minimum of 38 amp to a maximum of 130 amp. Some aspects of the J-change measurements of Malan and of Pierce are reexamined in the light of the magnitude and frequent occurrence of the continuing currents. It is concluded that earlier measurements of J changes for distances greater than 50 km must be interpreted as having been produced by the continuous flow of negative charge to earth instead of by the upward movement of positive charge contained within the cloud.