Molecular oxygen abundances in the thermosphere from Atmosphere Explorer-C ion composition measurements

We present a scheme for the daytime ion chemistry of O2+ in the thermosphere and use it to derive molecular oxygen abundances from ion composition measurements on board the Atmosphere Explorer-C satellite. The molecular oxygen abundance varies from about 1.0 × 108 to 5.0 × 108 cm−3 at 200 km. No seasonal variation is found, but a significant increase in mean O2 density occurs at high geomagnetic latitudes. We also find a small variation of the O2 density with local time.