Altitude of the red border in auroral forms

In very active forms the lower border of aurora can be red. This phenomen is induced by N 2 1PG emissions. An altitude of 60 to 100 km for the border where the green colour turns to the red one has been reported earlier. In this work, three substorms on 30 January, 1979 were studied to determine the altitude of the red lower border. A value of 85±2 km was obtained from colour film data of four different all-sky camera stations in northern Finland