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On the Relative Roles of Dynamics and Chemistry Governing the Abundance and Diurnal Variation of Low-Latitude Thermospheric Nitric Oxide

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We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics TIMED and the Aeronomy of Ice in the Mesosphere AIM satellites, in conjunction with model simulations from the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model TIME-GCM to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of lower thermospheric nitric oxide NO at near-solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment SOFIE to migrate down to low and mid-latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM one is driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and is free running at all other altitudes, and the other is constrained by a high-altitude analysis from the Navy Global Environmental Model NAVGEM up to the mesopause. We also compare SOFIE data with a NO climatology from the nitric oxide empirical model NOEM. Both SOFIE and NOEM yield peak NO abundances of around 4 x 107 cm-3 however, the SOFIE profile peaks about 6-8 km lower than NOEM. We show that this difference is likely a local time effect, with SOFIE being a dawn measurement and NOEM representing late morning andor near noon. The constrained version of TIME-GCM exhibits a low-altitude dawn peak, while the model that is forced solely at the lower boundary and free running above does no

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Journal Article - Open Access

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Annales Geophysicae , 37, 1, 01 Jan 0001, 01 Jan 0001,



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Approved For Public Release;

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