Evening Solar Terminator Waves in Earth's Thermosphere: Neutral Wind Signatures Observed by ICON-MIGHTI

Every evening, the sunset removes the primary energy input to the upper atmosphere, causing rapid atmospheric cooling and generating disturbances called solar terminator waves (STWs). Although they theoretically occur every night, STWs remain poorly understood, partially because the rapidly changing atmospheric conditions near sunset make measurements challenging. This study examines neutral wind measurements from the Michelson Interferometer for Global High-resolution Thermospheric Imaging (MIGHTI) on board NASA's Ionospheric Connection Explorer (ICON) observatory to uncover signatures of STWs. We report the north-south wind signatures of STWs and their altitude profile from 200 to 300 km, both of which have never been previously reported. We show that STWs are some of the largest amplitude dynamical features above 200 km near solstices, but are much weaker near equinoxes. By comparing our observations with the outputs of four different models, we find that STWs are likely generated directly or indirectly (from wave propagation) below 97 km. Future work is necessary to better understand how STWs are generated, how they vary on a daily basis, and the extent of their impacts on Earth's upper atmosphere.