On the response of thermospheric column O/N2 ratio variability to nonmigrating tides as seen by the Ionospheric Connection Explorer

The longitudinal dependence of the temperature and winds of the mesosphere/lower thermosphere at a constant local time is controlled largely by nonmigrating tides. It has been hypothesized that nonmigrating tides substantially impact the column number density ratio of atomic oxygen to molecular nitrogen (column O/N2 ratio), a diagnostic of thermospheric composition. However, the tidal variability in the column O/N2 ratio is not properly understood owing primarily to the impacts of ionospheric contamination at afternoon local times around the equatorial ionization anomaly. Observations of the column O/N2 ratio from the Far UltraViolet (FUV) instrument onboard the Ionospheric Connection Explorer (ICON) provide the opportunity to study nonmigrating tides at low latitudes. Here, we derive a clean column O/N2 ratio in order to delineate the response to nonmigrating tides as a function of local time. Estimates of the ionospheric contribution to 135.6 nm emission intensities based on Global Ionospheric Specification (GIS) model output, International Reference Ionosphere (IRI) model output, and observations from the Extreme UltraViolet imager onboard ICON are assessed.