Large-scale Gravity Waves in Daytime ICON-MIGHTI Data

The Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) onboard the NASA Ionospheric Connection Explorer (ICON) has retrieved profiles of wind and temperature in the 90-300 km range. 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 variations do not correlate with the retrieved winds or temperatures. However, there are time periods of observations where variations in the VER observations are strongly correlated with the wind and temperature observations, showing unexpectedly prominent, common large-scale structures. 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 ~3000 km for horizontal wavelengths and of ~35 km for vertical wavelengths. Currently we interpret these waves as inertia gravity waves. While observational evidence for such waves is not new, the unprecedented, global, long-term observations of these waves from 100 to 300 km by ICON allow for the most comprehensive characterization of their climatology to date.