An unusual two-stroke negative cloud-to-ground flash showing profuse branching and corona-like formations

摘要

An unusual natural lightning flash containing two negative strokes to ground was recorded at the Lightning Observatory in Gainesville (LOG), Florida, on June 8, 2013. The flash was apparently a bolt-from-the-blue, whose first-stroke leader emerged from the side of the cloud at a height of about 3.5 km above ground level. The first leader showed profuse branching and what appears to be corona-like formations with spatial extent of 100 to 200 m (probably an intensified portion of radial corona sheath) at the upper part of the channel. Leader branching process facilitated by two simultaneous space stems was observed. The corresponding step lengths were estimated to be 14 and 15 m. The first-stroke attachment process involved a streamer zone about 50 m in length. Second-stroke leader was also branched. One of the second-leader branches appeared to abruptly change its direction at the beginning of return stroke process.