The Molecular Oxygen Density Structure of the Lower Thermosphere as Seen by GOLD and Models

Oxygen chemistry plays a central role in the production of plasma in the ionosphere. While molecular oxygen (O2) is the third most abundant constituent in the thermosphere, molecular and atomic oxygen densities are difficult to quantify accurately. Consequently, modeled densities have significant uncertainties. New stellar occultation measurements from the GOLD (Global-scale Observations of Limb and Disk) mission provide data that can quantify, with high precision, the molecular oxygen density and its daily and local time variations. These observations are compared to the MSIS (Mass Spectrometer Incoherent Scatter radar) family of empirical models and the physics based Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (WACCM-X). While GOLD observations show a strong diurnal structure with local time, the models display a semidiurnal structure in molecular oxygen. The local time structure of molecular oxygen is critical for accurately modeling plasma densities in the ionosphere.