Unexpected Morphology and Dynamics of Lightning Continuing‐Current Channel as Seen in UV

Abstract Using a high‐speed imaging system operating in UV (290–370 nm) range at the Lightning Observatory in Gainesville (LOG), Florida, we observed, for the first time, what appeared to be lightning channel fragmentation starting <1 ms after the return‐stroke onset. The phenomenon was observed in 14 out of 15 strokes in 2 negative cloud‐to‐ground flashes at distances of a few hundred meters from LOG. Channel luminosity profiles exhibited pulsations, superimposed on the slowly‐varying UV luminosity waveform, with a typical period of some hundreds of microseconds over a typical time interval of some milliseconds. For higher‐order strokes, the pulsation time interval was longer, up to tens of milliseconds. The pulsation period was often influenced by the occurrence of M‐component. The presence of slowly‐varying UV luminosity and occurrence of M‐components during the pulsation time interval, along with the continuous visible‐range luminosity, are all indicative of the fragmented channel carrying a steady background current.