Atomic nitrogen densities in the thermosphere

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Abstract
Recently atomic nitrogen densities of ∼106cm−3 were measured at 400 km by the open source mass spectrometer on the Atmosphere Explorer‐C satellite (AE‐C). Daytime N densities ∼5 × 107cm−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 O2+ concentration than those measured on AE‐C over the altitude range to 160 to 200 km, because of the removal process O2+ + N k3 → NO+ + O. We show that the discrepancy can be explained in terms of latitudinal variations in both the N and O2 densities. We also present evidence which indicates that k3 could be as low as 1 × 10−10cm−3 at ionospheric temperatures.