Large-Scale Gravity Waves in Daytime ICON-MIGHTI Data from 2020

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) onboard the NASA Ionospheric Connection Explorer (ICON) has retrieved profiles of thermospheric wind and temperature in the 90-300 km range for over two years. As part of these limb-viewing measurements, MIGHTI also retrieves a relative volume emission rate (VER) of two atomic oxygen (OI) emissions in the same altitude range. Generally, the VER data do not vary in concert with the retrieved winds or temperatures. However, there are periods of observations where the VER measurements clearly vary together with the wind and temperature measurements, in unexpectedly prominent, large-scale structures. These large-scale variations are smaller than the tidal structures that are investigated as part of ICON's main mission. In this study, we present these large-scale variations as they appear together in the MIGHTI VER, zonal wind, and temperature products. We present a method to extract wave parameters from these structures and show their properties over the entire year of 2020. These large-scale waves consistently have vertical-to-horizontal slopes of 0.01 km/km, an upper-limit of similar to 3000 km for horizontal wavelengths and of similar to 35 km for vertical wavelengths. We interpret these waves as inertia gravity waves. While observational evidence for such waves is not new, it was not expected to observe their signatures with ICON data. Thus, this new global data set opens up a new and unique data source to explore this wave-type.