Evening Solar Terminator Waves in the Terrestrial Thermosphere: Neutral Wind Signatures Observed by ICON-MIGHTI

The solar terminator—the moving boundary between day and night in Earth's atmosphere—creates sharp heating gradients that result in atmospheric disturbances known as solar terminator waves (STWs). Although STWs may theoretically occur daily, they remain understudied, partially due to the observational challenges during rapidly changing atmospheric conditions near the solar terminator. Leveraging data from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) aboard NASA's Ionospheric Connection Explorer (ICON) observatory, we identify STW-related neutral wind features in the quiet-time thermosphere. Our analysis reveals the first observed meridional wind patterns linked to STWs and shows altitude profiles with large vertical wavelengths above 200 km. STWs are most pronounced during solstices, when they intersect the solar terminator approximately 20 degrees from the equator in the winter hemisphere and are inclined at around a 40-degree angle to the solar terminator. Comparisons with four whole-atmosphere models suggest that STWs originate, directly or indirectly, from waves below 97 km. These results indicate that STWs may play a larger role in quiet-time thermosphere-ionosphere variability than previously thought. We will also present preliminary findings on the variability of STWs.