On Thermospheric Molecular Oxygen and Its Relationship to Solar Activity

Observations from the Global-scale Observations of Limb and Disk (GOLD) mission have provided a new remote-sensing data source of molecular oxygen profiles in Earth's lower-to-middle thermosphere (120–200 km). GOLD O₂ observations indicate increasing densities of molecular oxygen at 170 km with rising solar activity between solar radio flux F10.7 values of 60 and ∼120 solar flux units (sfu). This is also seen in comparisons with solar extreme ultraviolet irradiance Q_EUV between 1 and ∼2.25 erg cm⁻² s⁻¹. However, the empirical Mass Spectrometer Incoherent Scatter radar 2.0 (MSIS 2.0) model overestimates O₂ densities at 170 km at these low levels of solar activity and predicts a decreasing density with increasing solar flux below ∼120 sfu. Additional data sets validate GOLD observations of O₂ and their relationship with solar activity. Accurately determining and forecasting O₂ is critical for accurately modeling plasma densities in the ionosphere and thermospheric density in the lower-to-middle thermosphere.