After days of intense solar activity, active region AR3664 launched seven CMEs towards Earth producing an extreme G5 geomagnetic storm commencing at 16:45 UT on Saturday May 10, 2024. The storm impacted power grids, disrupted precision navigational systems used by farming equipment, and generated aurora seen around the globe. The storm produced remarkable effects on composition, temperature, and dynamics in the Earth’s thermosphere that were observed by NASA’s Global-scale Observations of the Limb and Disk (GOLD) mission and are reported here for the first time. We use synoptic disk images of ΣO/N2 and neutral temperature (at ~160 km) measured by GOLD to directly link dynamics resulting from the storm with dramatic changes in thermospheric composition and temperature. We observe an apparent rotation simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator-to-pole temperature differences reach 400 K with peak neutral temperatures near 160 km exceeding 1400 K at high latitudes.

This work examines the weak stratospheric polar vortex (SPV) event of February 2008 and the strong SPV event of February 2021 to understand the potential influence of SPV strength on midlatitude thermospheric composition and ionospheric plasma density. The weak SPV event shows a reduction in thermospheric O/N2 at all longitudes, changes in the ionospheric total electron content (TEC) that vary with longitude, and an intensification of the semidiurnal tides. The strong SPV event shows O/N2 elevated by up to 25% in the Asian sector and a 25% decrease in semidiurnal tidal amplitude. The TEC response during the strong SPV event is complex, but shows enhanced TEC in the Asian sector where O/N2 is elevated. These are the first observations of anomalies in the thermospheric composition and ionospheric plasma associated with a strong polar vortex event.

The Global-scale Observations of the Limb and Disk (GOLD) Mission images middle thermosphere temperature and the vertical column density ratio of oxygen to molecular nitrogen (ΣO/N2) using its far ultraviolet imaging spectrographs in geostationary orbit. Since GOLD only measures these quantities during daylight, and only over the ~140º of longitude visible from geostationary orbit, previously developed tidal analysis techniques cannot be applied to the GOLD dataset. This paper presents a novel approach that deduces two specified non-migrating diurnal tides using simultaneous measurements of temperature and ΣO/N2. DE3 (diurnal eastward propagating wave 3) and DE2 (diurnal eastward propagating wave 2) during October 2018 and January 2020 are the focus of this paper. Sensitivity analyses using TIE-GCM simulations reveal that our approach reliably retrieves the true phases, whereas residual contributions from tides assumed to be absent, the restriction in longitude, and random uncertainty can lead to ~ 50% error in the retrieved amplitudes. Application of our approach to GOLD data during these time periods provides the first observations of non-migrating diurnal tides in measurements taken from geostationary orbit. We identify discrepancies between GOLD observations and TIE-GCM modeling. Retrieved tidal amplitudes from GOLD observations exceed their respective TIE-GCM amplitudes by a factor of two in some cases.

The middle thermospherefrom ~150 to 250 km is characterized by rapid increase in temperature with altitude and rapid ionization. The entire thermosphere is believed to be home to atmospheric waves that propagate through it, originating both in the atmospheric layers below and in the thermosphere itself. Within the middle thermosphere, direct observations of such waves are extremely sparse. The GOLD far-UV imaging spectrometer is able to observe the middle thermosphere from geostationary orbit. During October 2018 a special observational campaign was performed, designed to identify atmospheric waves. Signatures in the 135.6 nm O airglow were seen that move northwards with time, away from the Southern polar region. These are consistent with a large-scale atmospheric gravity wave. These results are the first time 135.6 nm airglow has been used to track such a wave and highlight the ability of GOLD to observe such waves, even when at a modest amplitude, and track their motion.

Travelling ionospheric disturbances (TIDs) and their neutral counterparts known as travelling atmospheric disturbances (TADs) are believed to play a central role in redistributing energy and momentum in the upper atmosphere and communicating inputs to other locations in the fluid. While these two phenomena are believed to be connected, they may not have a one-to-one correspondence as the geomagnetic field influences the TID but has no direct impact on the TAD. The relative amplitudes of the perturbations seen in the ionosphere and atmosphere have been observed but rarely together. This study reports results from a three-day campaign to observe TIDs and TADs simultaneously over a broad latitudinal region over the eastern United States using a combination of GOLD and a distributed network of ground based Global Navigation Satellite System (GNSS) receivers. These results demonstrate that GOLD and the ground-based total electron content (TEC) observations can see the atmospheric and ionospheric portions of a large-scale travelling disturbance. The phase difference in the perturbations to the GOLD airglow brightness, O/N2 and thermospheric disk temperature are consistent with an atmospheric gravity wave moving through this region. The ionospheric signatures move at the same rate as those in the atmosphere, but their amplitudes do not have a simple correspondence to the amplitude of the signal seen in the atmosphere. This campaign demonstrates a proof-of-concept that this combination of observations is able to provide information on TIDs and TADs, including quantifying their impact on the temperature and chemical composition of the upper atmosphere.

Themospheric conditions during a minor geomagnetic event of 3 and 4 February 2022 has been investigated using disk temperature (T$_{disk}$) observations from Global-scale Observations of the Limb and Disk (GOLD) mission and model simulations. GOLD observed that the T$_{disk}$ increases by more than 60 K during the storm event when compared with pre-storm quiet days. A comparison of the T$_{disk}$ with effective temperatures (i.e., a weighted average based on airglow emission layer) from Mass Spectrometer Incoherent Scatter radar version 2 (MSIS2) and Multiscale Atmosphere-Geospace Environment (MAGE) models shows that MAGE outperforms MSIS2 during this particular event. MAGE underestimates the T$_{eff}$ by about 2\%, whereas MSIS2 underestimates it by 7\%. As temperature enhancements lead to an expansion of the thermosphere and resulting density changes, the value of the temperature enhancement observed by GOLD can be utilized to find a GOLD equivalent MSIS2 (GOLD-MSIS) simulation $\textendash$ from a set of MSIS2 runs obtained by varying geomagnetic ap index values. From the MSIS2 runs we find that an ap value of 116 nT produces a T$_{eff}$ perturbation that matches with the GOLD T$_{disk}$ enhancement. Note that during this storm the highest value of the 3 hr cadence ap was 56 nT. From the MSIS-GOLD run we found that the thermospheric density enhancement varies with altitude from 15\% (at 150 km) to 80\% (at 500 km). Independent simulations from the MAGE model also show a comparable enhancement in neutral density. These results suggest that even a modest storm could impact the thermospheric densities significantly.

The strongest Southern Hemisphere minor sudden stratospheric warming (SSW) in the last 40 years occurred in September 2019 and resulted in unprecedented weakening of the stratospheric polar vortex. Ionospheric total electron content (TEC) observations are used to provide an overview of statistically significant anomalies in the low-latitude ionosphere during this event. Quasi-semidiurnal perturbations of TEC are observed in response to the SSW, similar to those seen during Northern Hemisphere SSWs. Analysis indicates the existence of quasi-periodic oscillations in TEC in the crests of the equatorial ionization anomaly, with strong 5-6 day and 2-3 day periodicities. Ionospheric anomalies from the combined effects of multiple mechanisms exceed a factor of 2, comparable to the strongest anomalies associated with Northern Hemisphere SSWs. These results also indicate, for the first time, a remarkable longitudinal variation in the character and magnitude of variations that could be related to a modulation of the non-migrating diurnal tide.