Observations of corona in triggered dart‐stepped leaders

Corona streamers are a critical component of lightning leader step formation and are postulated to produce the very high electric fields at their tips that produce runaway electrons resulting in the observed X-ray bursts associated with leader stepping. Corona emanating from the vicinity of the leader tip between leader steps was analyzed using three sequential high-speed video sequences of dart-stepped leaders in three different triggered lightning flashes during the summers of 2013 and 2014 in northeast Florida. Images were recorded at 648 kiloframes per second (1.16 mu s exposure time, 380ns dead time) at an altitude of 65m or less. In each image sequence, the leader propagates downward in consecutive frames, with corona streamers observed to fan outward from the bright leader tip in less than the image frame time of about 1.5 mu s. In 21 exposures, corona streamers propagate, on average, 9m below the bright leader tip.