The Eclipse-Induced NO Cooling Changes Investigated by the Simultaneous SABER and GOLD Measurements and Numerical Simulations on 14 October 2023

Nitric oxide (NO), a minor constituent of the Earth's lower thermosphere, emits 5.3-μm infrared radiation, causing an important cooling effect on the thermosphere. In this study, the eclipse-induced NO cooling changes are investigated using the SABER and GOLD measurements and the Thermosphere-Ionosphere modeling of the 14 October 2023 eclipse. The observations show a NO cooling depletion (∼4 erg/cm³/s, ∼40%) in SABER measurements that is concurrent with a reduction in neutral temperature (∼60 K) in GOLD observations around 150 km altitude, associated with an increased O/N2 ratio. The Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIEGCM) captures the morphology of the eclipse-induced effects but underestimates the observed variations. The data-model comparison confirms this depletion caused by the decreased NO density and temperature. Model term analysis shows that the eclipse-induced decrease in NO density is mainly produced by the chemical process instead of dynamic transport. The temperature-dependent reaction rate of NO production from Duff et al. (2003, https://doi.org/10.1029/2002GL016720) was further tested and quantified the cooling depletion better. However, there still exists a discrepancy in neutral temperature changes. This study presents multi-source observations of eclipse-induced NO cooling changes, and contributes to the understanding of cooling processes in the thermosphere-ionosphere system.