Drivers of Nighttime CO2 Non-Local Thermodynamic Equilibrium

This study investigates the drivers of nighttime CO2 non-local thermodynamic equilibrium (NLTE) in the polar lower thermosphere. Daytime NLTE is well understood to be influenced by solar radiation, but nighttime NLTE is far less understood. Our goal is to quantify whether nighttime NLTE is a consistent signature of aurora or a result of coupling between aurora and atmospheric dynamics. We find that nighttime NLTE increases are associated with auroral activity and atmospheric gravity waves. We use the AIRS NLTE index (Bossert et al., 2023), which is derived from CO2 4.26-μm emissions, to find a link between NLTE and electron densities, as measured by Poker Flat Incoherent Scatter Radar. Additionally, we have developed a classification system to identify nighttime CO2 NLTE increases suspected to be driven by auroral particle precipitation and gravity wave-driven perturbations; these drivers will be further investigated in future work.