Solar Terminator Waves Revealed as Dominant Features of Upper Thermospheric Density

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 three near 500 [km]. The study analyzes STWs in TMD data across altitude, solar cycle, local solar time, and both solstices, demonstrating enhanced dawn-dusk symmetry near 500 [km]. By directly comparing CHAMP and GRACE-FO measurements with output from the High-Accuracy Satellite Drag Model (HASDM), this study provides a more physically representative characterization of STW magnitudes than prior approaches which have estimated STW amplitudes by filtering along the orbit. The broader impact of these features on POD-derived density datasets is also explored, highlighting their role in shaping the interpretation of satellite drag in the upper thermosphere. 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.