Thermospheric temperature and ΣO/N2 variations as observed by GOLD and compared to MSIS and WACCM-X simulations during 2019-2020 at deep solar minimum

The ultraviolet-imaging spectrograph that comprises Global-scale Observations of the Limb and Disk (GOLD) mission in geostationary orbit at 47.5 degrees W longitude has taken full disk images at high cadence throughout the deep solar minimum period of 2019-2020. Synoptic (i.e., concurrent and spatially unified and resolved) observations of thermospheric temperature and composition at similar to 150 km altitude are made for the first time, allowing GOLD to disambiguate temporal and spatial variations. Here we analyze the daytime effective temperature and column integrated O and N-2 density ratio (Sigma O/N-2) data simultaneously observed by GOLD over 120 degrees W-20 degrees E longitude and 60 degrees S-60 degrees N latitude from 13 October 2019 to 12 October 2020. Daily zonal mean values are calculated for each latitude and compared with NRLMSIS 2.0 and simulations from the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (WACCM-X). On average, the GOLD observations show higher temperatures than Mass Spectrometer Incoherent Scatter radar (MSIS) and WACCM-X by similar to 20-60 K (5%-10%) and 80-120 K (12%-18%), respectively. The Sigma O/N-2 ratios observed by GOLD are larger than the MSIS results by similar to 0.4 (40%) but smaller than the WACCM-X simulations by similar to 0.3 (30%). The observed and modeled results are correlated at most latitudes (r = 0.4-0.8), and GOLD, MSIS, and WACCM-X all display a similar seasonal variation and change with latitude. WACCM-X simulates a larger annual variation in Sigma O/N-2, suggesting that the thermospheric circulation is overestimated and atmospheric waves and turbulence transport are not properly represented in the model.