Solar Terminator Waves Revealed as Dominant Features of Upper Thermospheric Density

Abstract Observations of solar terminator waves (STWs) in thermospheric mass density (TMD) measurements above 500 km reveal STWs as dominant features of the upper thermosphere. While previous investigations have shown that STWs in the middle‐lower thermosphere have amplitudes on the order of 6%–8% of the background TMD in that region, this study shows that STWs exhibit a striking amplification with altitude, producing density perturbations of up to a factor of two near 500 km. The study analyzes STWs in TMD data across altitude, solar cycle, and both solstices, leveraging a direct comparative methodology with Challenging Minisatellite Payload, Gravity Recovery and Climate Experiment Follow‐On, and High‐Accuracy Satellite Drag Model. The first detection of a dawn STW with a magnitude comparable to dusk is made near 500 km, contrasting the asymmetry seen at lower altitudes. The newfound prominence of STWs highlights the need for further research into their generation mechanisms, role in geophysical variability, and broader implications for thermospheric modeling and spacecraft operations.