Positive leader characteristics from high-speed video observations

Based on analyses of high‐speed video recordings of cloud‐to‐ground lightning in Brazil and the USA, the characteristics of positive cloud‐to‐ground (+CG) leaders are presented. The high frame rates permitted the average, 2‐dimensional speeds of development along the paths of the channels to be resolved with good accuracy. The values range from 0.3 to 6.0 × 105 ms−1 with a mean of 2.7 × 105 ms−1. Contrary to what is usually assumed, downward +CG leader speeds are similar to downward −CG leader speeds. Our observations also show that the speeds tend to increase by a factor of 1.1 to 6.5 as they approach the ground. The presence of short duration, recoil leaders (RLs) during the development of positive leaders reveal a highly branched structure that is not usually recorded when using conventional photographic and video cameras. The existence of the RLs may help to explain observations of UHF‐VHF radiation during the development of +CG flashes.