Argon auroral emissions

Argon is the third most abundant constituent of the atmosphere, but has not been previously detected by any ground-based optical remote sensing method. We report observation of argon emissions at λ840.82 and λ842.46nm during intense aurora. These are most likely excited by direct electron impact. The maximum argon intensity observed is 270R. Argon is the fifth elemental emission conclusively observed in geo-aurora, joining N, O, H and He.