Abstract. An auroral electron excitation model, combined with simple equilibrium neutral and ion chemistry models, is used to investigate the optical emission processes and height profiles of I(5577 Å) and I(7620 Å) in the 90 to 100 km altitude region. It is shown that the apparent discrepancies between ground-based and rocket-borne auroral observations of the I(7620 Å)/I(5577 Å) ratio are due to the extreme height variation of this intensity ratio in the 90 to 100 km region.Key words. Atmospheric composition and structure (airglow and aurora)