Leader and Return Stroke Velocity Measurements in Lightning From a Tall Chimney

Abstract

Velocities of lightning leader and return strokes were measured with the optical detectors in two ground flashes (flash G-20 and flash G-22) initiated by upward streamers from a tall chimney. Dart-type leaders are confirmed both on the light signals and on the electric field changes. The leader propagating downward with a speed of 9×10⁶m/s is noted in the flash G-20. 17 impulsive light signals are found to precede a return stroke signal in the development of upward streamers. On the three negative return strokes following downward dart-type leaders in G-2U and G-22, the direction of the propagation is found to be upward and the speed is found to range from 1.2×10⁸m/s to 2.3×10⁸m/s.