A method is described to determine the concentration of atomic oxygen in the altitude range 100 to 160 km in an aurora from the ratio of the volume emission rates of the O(1S) 5577¿ to N2+ in 3914¿ emissions. Applying the technique to previously published measurements it is found that the O density at 100 km is typically about 1¿1011cm-3 in the aurora at 100 km is rare. |