Atomic nitrogen densities in the thermosphere

Recently atomic nitrogen densities of ∼10 6 cm −3 were measured at 400 km by the open source mass spectrometer on the Atmosphere Explorer‐C satellite (AE‐C). Daytime N densities ∼5 × 10 7 cm −3 at 160 km have also been inferred from airglow and other measurements on AE‐C. We show that atomic nitrogen densities of this magnitude result in significantly lower values for the O 2 + concentration than those measured on AE‐C over the altitude range to 160 to 200 km, because of the removal process O 2 + + N k 3 → NO + + O. We show that the discrepancy can be explained in terms of latitudinal variations in both the N and O 2 densities. We also present evidence which indicates that k 3 could be as low as 1 × 10 −10 cm −3 at ionospheric temperatures.