High-Speed Spectra Of A Bolt From The Blue Lightning Stepped Leader

We present spectra from 400 to 900 nm of a bolt from the blue stepped leader on July 19, 2015 including novel observations from 400 to 600 nm. The spectra of the luminous steps near the tip of the leader look qualitatively similar and contain singly ionized nitrogen lines. The presence of these ionized lines indicate currents and temperatures comparable to peak return stroke. The entire channel illuminates over the final 1.3 ms before attachment, but does not contain evidence of ionization. This neutral spectrum is qualitatively similar to the return stroke spectrum after peak current. This may indicate increasing potential and current along the channel prior to attachment.