Spectral characteristics of lightning dart leader propagating in long path

Cloud-to-ground lightning with six return strokes has been recorded with high-speed slitless spectrograph at a recording rate of 9110 frames per second. The dart leaders propagate along the same channel which consists of a long horizontal path and a vertical path, and its speed at the horizontal path is faster than that at the vertical path. The first-order spectrum of dart leader is recorded with an exposure time of 110 μs. The wavelength observed in dart leader spectrum is firstly extended to near infrared range. The spectral characteristics indicate that all the emission lines in the 400-700 nm range are radiated from singly ionized nitrogen except the Hα line at 656.3 nm, and in the range of 700-1000 nm the emission lines are radiated from neutral nitrogen and oxygen.