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The Global‐scale Observations of Limb and Disk (GOLD) imagers scan the Earth's Thermosphere‐Ionosphere (TI) in the far ultraviolet wavelengths. Measurements from GOLD daylit spectrum are used to retrieve the column integrated atomic oxygen to molecular nitrogen density ratio (O/N2) over about one fourth of the globe. The present investigation assesses the impact of assimilating GOLD disk O/N2 on the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCMX) using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter. Two Observing System Simulation Experiments (OSSEs) are performed, and improvements are quantified by calculating root mean square error (RMSE) and bias with respect to a truth run. In addition to solar and geomagnetic forcing, we introduced gravity wave forcing perturbations to increase the ensemble spread, which has not previously been applied in ensemble assimilation. One of the OSSEs assimilates only the lower atmosphere (LA, < ${< } $100 km) observations, referred to as LA experiment, and the second assimilates GOLD O/N2 and LA observations, referred to as Whole Atmosphere (WA) experiment. The WA‐analysis O/N2 RMSE and bias are about 60% and 87% better compared to LA‐analysis. Also, the O/N2 RMSE and bias for the WA‐analysis are about 23% and 54% better compared to WA 1‐hr forecasts. The improvement in WA electron column density (ECD), a model equivalent of Total Electron Content (TEC), is about 24% compared to the LA experiment. These results demonstrate that the assimilation of GOLD O/N2 improves both the thermosphere and ionosphere in a whole atmosphere data assimilation system. Plain Language Summary: To be able to nowcast and forecast the Thermosphere‐Ionosphere (TI) weather we need to demonstrate that the currently available whole atmosphere‐ionosphere‐thermosphere model results can be improved by adjusting their states based on the available observations. In this work we demonstrate a potential scenario, by employing Observing System Simulation Experiments (OSSE), where the use of NASA GOLD mission column integrated ratio of atomic oxygen to molecular nitrogen (O/N2) improves the analysis and short term forecast states in the Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCMX) compared to only assimilating observations below ∼ ${\sim} $100 km. These improvements suggest that assimilation of GOLD observations can be potentially beneficial to space weather forecasting models. Key Points: Synthetic GOLD disk O/N2 observations are assimilated in WACCMX + DARTGravity wave forcing perturbations are introduced to improve the ensemble spreadThe assimilation improves analysis RMSE and bias in O/N2 by 23%–60% and 54%–87%, depending on the reference chosen [ABSTRACT FROM AUTHOR]

After days of intense solar activity, active region AR3664 launched seven CMEs toward Earth producing an extreme G5 geomagnetic storm commencing at 17:05 UT on 10 May 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 a heretofore unseen spatial morphology simultaneously in ΣO/N2, neutral temperature, and total electron content. Equator‐to‐pole temperature differences reach 400 K with high latitude peak neutral temperatures near 160 km exceeding 1400 K. Plain Language Summary: On Saturday 10 May 2024, the sun launched a wave of energized plasma toward the Earth. A large disturbance in the Earth's magnetic field associated with the solar wind resulted in an extreme geomagnetic storm. The storm impacted power grids, disrupted navigational systems used by farming equipment, and produced aurora seen around the globe. The storm produced remarkable effects in the Earth's upper atmosphere that were observed by NASA's Global‐scale Observations of the Limb and Disk (GOLD) mission. In this letter, we use images measured by GOLD to directly link atmospheric dynamics resulting from the May 10–12 superstorm with dramatic changes in composition, temperature, and global circulation in the Earth's upper atmosphere. We observe previously unseen structure in the upper atmosphere associated with equator‐to‐pole temperature differences exceeding 400 K. Peak neutral temperatures near 160 km exceed 1400 K at high latitudes. Key Points: GOLD disk images of ΣO/N2 and neutral temperature link storm time dynamics with changes in thermospheric composition and temperatureWe observe a previously unseen spatial morphology in ΣO/N2, neutral temperature, and total electron contentPeak equator‐to‐pole temperature differences exceed 400 K but relax to pre‐storm conditions well before ΣO/N2 [ABSTRACT FROM AUTHOR]

A unique phenomenon--A geomagnetically quiet time merging of Equatorial Ionization Anomaly (EIA) crests, leading to an X-pattern (EIA-X) around the magnetic equator--has been observed in the night-time ionospheric measurements by the Global-scale Observations of the Limb and Disk mission. The pattern is also reproduced in an ionospheric model that assimilates slant Total Electron Content from Global Navigation Satellite System and Constellation Observing System for Meteorology, Ionosphere, and Climate 2. A free-running whole atmospheric general circulation model simulation reproduces a similar pattern. Due to the similarity between measurements and simulations, the latter is used to diagnose this heretofore unexplained phenomenon. The simulation shows that the EIA-X can occur during geomagnetically quiet conditions and in the afternoon to evening sector at a longitude where the vertical drift is downward. The downward vertical drift is a necessary but not sufficient condition. The simulation was performed under constant low-solar and quiescent-geomagnetic forcing conditions, therefore we conclude that EIA-X can be driven by lower-atmospheric forcing. [ABSTRACT FROM AUTHOR]

The 2022 Tongan volcanic eruption released significant energy into the atmosphere. Tropospheric satellite images show that the eruption generated pressure waves that traveled globally. The Global Observation of the Limb and Disk (GOLD) mission observed significant wave‐like thermospheric temperature perturbations (>100 K) from 12 to 16 UT. These temperature perturbations' spatial curvatures and arrival times are initially similar to the tropospheric wave‐fronts but differ significantly with eastward propagation. The perturbations had a phase speed of ∼300–400 m/s and wavelengths greater than 2,400 km. Near‐concurrent Ionospheric Connection Explorer neutral wind measurements suggest that the eruption's effects reversed the direction of the prevailing thermospheric zonal winds around the perturbed regions. The eruption's global and whole atmospheric effects provide a unique opportunity to study how different atmospheric layers exchange energy and momentum during explosive events. GOLD's synoptic observations are uniquely positioned to study these effects in the middle thermosphere. Plain Language Summary: The powerful Hunga Tonga‐Hunga Ha'apai volcanic eruption on 15 January 2022, at 4:15 UT was visible from space. Satellite images in the troposphere (near 10 km altitude) show concentric pressure waves emanating from the eruption center that travel globally. Wave signatures were seen across multiple atmospheric layers. NASA's Global‐scale Observations of Limb and Disk mission observed its signatures near 150 km altitude as neutral temperature perturbations. Explosive events that affect multiple atmospheric layers allow us to observe how the different atmospheric layers exchange energy and momentum in response to an impulsive source. In this paper, we present an analysis of the eruption induced temperature perturbation in the middle thermosphere. Key Points: Global‐scale Observations of Limb and Disk mission observed global‐scale thermospheric neutral temperature perturbations (>100 K) induced by the Tongan volcanic eruptionThe phase speeds of the perturbations are around 300–400 m/s with a large wavelength (>2,400 km)The zonal winds near the peak temperature perturbation reverse from eastward to westward [ABSTRACT FROM AUTHOR]

The geomagnetic storm on February 3, 2022 caused the loss of 38 Starlink satellites of Space‐X. The Global‐scale Observations of the Limb and Disk (GOLD) observations and Multi‐Scale Atmosphere Geospace Environment (MAGE) model simulations are utilized to investigate the thermospheric composition responses to the Space‐X storm. The percentage difference of the GOLD observed thermospheric O and N2 column density ratio (∑O/N2) between the storm time (February 3, Day‐of‐Year [DOY] 34) and quiet time (DOY 32) shows a depletion region in the local noon sector mid‐high latitudes in the southern hemisphere, which corresponds to the east side of GOLD field‐of‐view (FOV). This is different from the classic theory of thermospheric composition disturbance during geomagnetic storms, under which the ∑O/N2 depletion is usually generated at local midnight and high latitudes, and thus, appear on the west side of GOLD FOV. MAGE simulations reproduce the observations qualitatively and indicate that the ∑O/N2 depletion is formed due to strong upwelling in the local morning caused by strong Joule heating. Interestingly, enhanced equatorward winds appear near local midnight, but also in the local morning sector, which transports ∑O/N2 depletion equatorward. The depletion corotates toward the local afternoon and is observed in the GOLD FOV. The equatorward winds in the local morning are due to the ion‐neutral coupling under the conditions of a dominant positive interplanetary magnetic field east‐west component (By) during the storm. Key Points: Global‐scale Observations of the Limb and Disk (GOLD) observed a southern hemisphere ∑O/N2 depletion on the east side of its field‐of‐view (local afternoon)The GOLD observed southern ∑O/N2 is different from the classical theory of the thermosphere composition response to geomagnetic stormsSimulation shows that the observed ∑O/N2 depletion is generated in local morning, and transported equatorward, corotated to later local times [ABSTRACT FROM AUTHOR]

The National Aeronautics and Space Administration Global-scale Observations of the Limb and Disk (GOLD) mission observed a unique structure of thermospheric column density ratio of O to N2 (ΣO/N2) during a geomagnetic storm on day of year (DOY) 130 (May 10) to DOY 132 in 2019. The percentage difference of ΣO/N2 between the storm time (DOY 131) and the quiet time (DOY 128) had a relatively enhanced ΣO/N2 region sandwiched by two depleted regions over North America and the Atlantic Ocean in the Northern Hemisphere. This enhanced ΣO/N2 region is called the neutral tongue here. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model also predicted a similar ΣO/N2 structure with the same spatial and temporal evolution as that seen in the GOLD observations on DOY 131. Model diagnostic analysis revealed that the neutral tongue was formed when the neutral wind in the region changed from mostly equatorward to poleward, which transported the ΣO/N2 rich air from lower latitudes into this longitude section, forming the neutral tongue. The neutral tongue separated a large depletion region formed earlier into two smaller depleted regions, one on each side of the neutral tongue. [ABSTRACT FROM AUTHOR]