Branched dart leaders preceding lightning return strokes. Issue 7 (14th April 2014) - Stolzenburg, Maribeth
Abstract: This study describes the occurrence of branches in lightning dart leaders, based on data acquired in Florida using a high‐speed video camera and electric field change sensors. More than half (57%) of 72 flashes with analyzable dart leaders show at least one successful branched dart leader (BDL), and nine flashes have two successful BDLs. Overall, 18% of 282 visible successful dart leaders are branched. Most (42 of 50) cases of BDLs occur in the first dart leader after a stepped leader/return stroke sequence, and the data indicate that 55% of first dart leaders are visibly branched. Compared to first dart leaders in the 31 flashes without any branched dart leaders, BDLs tend to follow stepped leader/return strokes with significantly larger average peak currents (−31.3 versus −20.6 kA) and shorter average interstroke intervals (71.94 versus 94.64 ms). Average peak current of BDL strokes is 62% larger (−17.8 versus −11 kA) than that for unbranched first dart leader strokes. Branched dart leaders generally travel in the some of the most recently used lightning channels, but they are not always within the main channel of the prior return stroke. Successful BDLs may dart all the way to ground when in a prior stroke channel, or they may become stepped leaders when they reach the lower end of the prior stroke branch. Electric field change data for all the BDL cases exhibit an erratic pulse character for at least part of the leader duration; in some cases, the erratic character ends when the branches vanish. Key Points: Video data show 57% of 72 flashes have a successful branched dart leader (BDL) BDLs are often the first dart leaders in a flash and can miss the prior channel Ratio of preceding peak current to interstroke interval for BDLs is 2x larger