Return stroke velocity of a lightning discharge

My purpose in the present note is to discuss a new empirical relation for the velocity of the first return streamer in a lightning discharge. Observations of Bruce and Golde [1941] and others [Thomas and Burgess, 1947], showed that in a cloud-to-ground discharge the velocity of the first return streamer, extending from the ground to the negative charge center of the overhead thunder cloud along the discharge channel already blazed by the downward leader, could be expressed by the following empirical relation: where, V0 = 9 × 107 m/sec and v = 3 × 104 sec−1. In strokes after the first of the lightning flashes, the velocities of the return strokes are remarkably uniform [Schonland, 1956] throughout their passage from the ground to the cloud, and these will not be discussed.