Electron density measurement of a lightning stepped leader by oxygen spectral lines

The time-resolved spectrum of a lightning stepped leader in downward process has been obtained by using a slitless spectrograph. Neutral oxygen and nitrogen spectral lines in the near infrared region are observed in the spectra. The electron density of the lightning stepped leader was calculated by using the Stark broadening of the oxygen spectral lines at 777.4 and 844.6 nm. The evolution characteristic of the electron density with time and channel height of the lightning stepped leader was analysed. The results shown that the electron density of the lightning stepped leader was in the order of 1018 cm-3. The electron density decreased when the lightning stepped leader propagates downward to ground.