First Results From the Retrieved Column O/N2 Ratio From the Ionospheric Connection Explorer (ICON): Evidence of the Impacts of Nonmigrating Tides. Issue 9 (10th September 2021) - England, Scott L.
Abstract: In near‐Earth space, variations in thermospheric composition have important implications for thermosphere‐ionosphere coupling. The ratio of O to N2 is often measured using far‐UV airglow observations. Taking such airglow observations from space, looking below the Earth's limb allows for the total column of O and N2 in the ionosphere to be determined. While these observations have enabled many previous studies, determining the impact of nonmigrating tides on thermospheric composition has proved difficult, owing to a small contamination of the signal by recombination of ionospheric O + . New ICON observations of far‐UV are presented here, and their general characteristics are shown. Using these, along with other observations and a global circulation model, we show that during the morning hours and at latitudes away from the peak of the equatorial ionospheric anomaly, the impact of nonmigrating tides on thermospheric composition can be observed. During March–April 2020, the column O/N2 ratio was seen to vary by 3–4% of the zonal mean. By comparing the amplitude of the variation observed with that in the model, both the utility of these observations and a pathway to enable future studies is shown. Plain Language Summary: At high altitude in the atmosphere, mixing of the gas via turbulence becomes less important, and mix of atmospheric species begins to vary with altitude, depending on the mass of the atom or molecule. At these altitudes, the composition of the atmosphere can vary greatly with location and time in a manner not seen in the lower levels of the atmosphere. This same high‐altitude region overlaps with the charged particle environment known as the Earth's ionosphere. How the atmosphere and ionosphere interact is in‐part determined by the composition of the atmosphere. Measuring this composition is therefore important and is done regularly using observations in the far‐ultraviolet. These reveal much of the compositional variation, but a small contaminating signal from the ionosphere has made detecting some small changes produced by waves in the atmosphere a challenge. Here, new observations in the far‐UV are introduced and their general properties shown. By selecting a specific location and time and utilizing supporting data and a global model, we are able to show the change in the composition produced by a certain class of wave in the atmosphere. This demonstrates the utility of these new observations and provides a pathway to futures studies. Key Points: An initial overview of the Ionospheric Connection Explorer‐far‐ultraviolet sublimb observations and derived column O/N2 ratios is presented In the morning, away from the equatorial ionosphere, the impact of nonmigrating tides on O/N2 is shown clearly for the first time Comparison of the tidal signature with the TIEGCM highlights basic agreement, with possible discrepancy in tidal vertical wavelength