Global Ionosphere Thermosphere Model (GITM) results have been compared with measurements from Global-scale Observations of the Limb and Disk (GOLD) and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). For the first time, GOLD-derived exospheric temperature and column-integrated O/N$_2$ ratio measurements have been used to validate GITM model results. We examine two geomagnetic storm events for which we drive GITM with space weather conditions to understand how well the model reproduces the thermospheric responses to geomagnetic activity. In this paper, a recently developed auroral model, the Feature Tracking of Aurora (FTA) model, has been employed to calculate auroral electron precipitation in GITM (GITM w/FTA), and results are compared with the OVATION prime (OP) driven GITM model (GITM w/OP). GITM w/FTA simulated temperature, neutral density, and nitric oxide (NO) density are generally higher compared to the GITM w/OP model. During the geomagnetic storm, the GITM model and GOLD-derived exospheric temperature agree between $\sim$$0^{\circ}$ to $5^{\circ}$N latitude in the equatorial region. GOLD measurements show strong O/N$_2$ peaks and two distinct equatorial zones during the geomagnetic storm period, which is also observed in our model results. During geomagnetic storm conditions, there is an upward shift in the peak altitude profile of NO emission by up to $\approx$10 km. The NO cooling peaks estimated by GITM models are $\sim$20 km lower than SABER observations during geomagnetic storms. The SABER-derived NO emission is better reproduced by the GITM w/FTA model than by the GITM w/OP model during geomagnetic storms at high latitudes.

Accurate modeling of thermospheric impact of high solar and geomagnetic activities is crucial for safeguarding our space-based infrastructure. However, current modeling capabilities are still unable to accurately predict thermospheric density, which is a key parameter for calculating satellite drags. In this paper, we performed global sensitivity analysis (GSA) for nitric oxide (NO)-related chemical reaction rates using the Global Ionosphere Thermosphere Model (GITM) during solar maximum and solar minimum conditions. We have performed GSA and uncertainty quantification (UQ) for the first time in GITM. GITM is a computationally expensive model; therefore, we employed a Gaussian process (GP)-based surrogate model to approximate the thermospheric states of GITM and inexpensively generate samples for Monte-Carlo-based Sobol analysis. We computed first-order (main effect) and total-order (total effect) Sobol’ sensitivity indices to quantify how the uncertainty associated with NO-related chemical reaction rate coefficients in GITM influences the variance of the NO density, NO cooling rate, temperature, and neutral density. Our study identified the most influential reaction rates the uncertainty of which contribute to the most uncertainty in estimating thermospheric states in GITM and provided important information for UQ within GITM to accurately estimate the thermospheric density. Our findings suggest that reducing the uncertainty in the reaction rates, particularly for RR43 ($NO + hv ightarrow N ({}^4 S) + O$), RR44 ($N({}^4 S) + O_2 ightarrow NO + O$), and RR5 ($N_2^+ + O ightarrow NO^+ ({}^2 D) + N ({}^2 D)$), should be prioritized to fix GITM’s response to variations in F10.7 solar flux.