Using NASA’s Global-scale Observations of the Limb and Disk (GOLD) imager, we report nightside ionospheric changes during the G5 super geomagnetic storm of 10-11 May 2024. Specifically, the nightside southern crest of the Equatorial Ionization Anomaly (EIA) was observed to merge with the aurora near the southern tip of South America. During the storm, the EIA southern crest was seen moving poleward as fast as 450 m/s. Furthermore, the aurora extended to mid-latitudes reaching the southern tips of Africa and South America. The poleward shift of the equatorial ionospheric structure and equatorward motion of the aurora means there was no mid-latitude ionosphere in this region. These observations offer unique insights into the ionospheric response to extreme geomagnetic disturbances, highlighting the complex interplay between solar activity and Earth’s upper atmosphere.

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.

Observations of far-ultraviolet (FUV) dayglow by the Global-scale Observations of Limb and Disk (GOLD) mission provide an opportunity for quantifying the global-scale response of the thermosphere to solar extreme-ultraviolet (EUV) variability and geomagnetic activity. Relative temperature changes can be measured by monitoring changes in the rotational structure observed in molecular nitrogen Lyman-Birge-Hopfield (LBH) band emissions. We present a new technique for deriving neutral temperatures from GOLD FUV observations using optimal estimation fits to spectra containing LBH band emissions. We provide an overview of the theoretical basis for the GOLD Level 2 neutral temperature algorithm. Effects on derived neutral temperatures from instrument artifacts and particle background are reviewed. We also discuss GOLD Level 1C DAY and Level 2 TDISK data products and present representative examples of each. We show that neutral temperatures vary with local time, exhibit a strong seasonal dependence, and correlate strongly with geomagnetic and solar activity. Finally, we present results from a preliminary data product validation that show good agreement with coincident GOLD exospheric temperatures and predictions from a global reference atmospheric model.

A document by Deepak Kumar Karan. Click on the document to view its contents.

A unique phenomenon {\textendash} merging of Equatorial Ionization Anomaly (EIA) crests, leading to an X-pattern (EIA-X) around the magnetic equator {\textendash} has been observed in the night-time ionospheric measurements by the Global-scale Observations of the Limb and Disk (GOLD) mission. A whole atmospheric general circulation model simulation reproduces this pattern. The pattern is also produced in an assimilative ionosphere model that assimilates slant Total Electron Content (slant-TEC) from Global Navigation Satellite System (GNSS) and Constellation Observing System for Meteorology, Ionosphere, and Climate 2 (COSMIC-2). Due to the observed similarity between measurements and simulations, the latter is used to diagnose this heretofore unexplained phenomenon. The simulation shows that the EIA-X occurs in the afternoon to evening sector at a longitude where the vertical drift is negative, which is a necessary but not sufficient condition. The simulation was performed under constant low-solar and quiescent-geomagnetic forcing conditions, therefore we suggest that one of the drivers of this phenomenon is from lower-atmospheric processes.

The recovery of the thermosphere after a strong geomagnetic storm on 12 May 2021 is investigated using lower and middle thermospheric temperature (Tdisk), ratio of atomic oxygen and molecular nitrogen column densities (O/N2), cooling due to Nitric Oxide (NO), and model simulations. The peak influence of the geomagnetic storm lasted about five hours and generated latitudinal gradients in Tdisk and O/N2. Following the storm, the latitudinal gradient in temperature recovered faster compared to that of O/N2. Measured NO-cooling rate and simulated NO-densities are enhanced on the storm day compared to a quiet-day, consistent with a rapid recovery in temperatures. Based on this, we conclude that the faster recovery of the Tdisk latitudinal gradient is driven by the combined effect of NO cooling and strong thermal conductivity. Furthermore, the slower recovery of the O/N2 latitudinal gradients can be attributed to the lack of poleward advection after the storm.

On 12 October 2020 and 26 December 2021, NASA’s Global-scale Observations of the Limb and Disk (GOLD) mission observed differently shaped EPBs simultaneously within ~10o longitude, near the subsatellite point and over the Atlantic, respectively which is unusual. On 12 October 2020, three EPBs with differing curvatures were observed in a ~12o longitude sector. The westside EPB was curved towards the east, in a C-shape. The middle was straight. The eastside EPB was curved westward, in a reversed C-shape. In the second case, 26 December 2021, in a smaller longitude range of ~6o adjacent C-shaped and reversed C-shaped EPBs were observed. EPBs’ zonal drift velocities at the magnetic equator and both EIA crests were compared. These occurrences of oppositely shaped EPBs simultaneously in a narrow longitude may indicate that small-scale longitudinal variations in the E-region density, electric field, neutral wind variations, or a combination of them were present.

A document by Richard W Eastes. Click on the document to view its contents.

On 12 October 2020, the NASA’s Global-scale Observations of the Limb and Disk (GOLD) mission observed three differently shaped EPBs within a 12o longitude range, near the subsatellite point. One is straight aligned to the magnetic field line, whereas the poleward extensions of the others are tilted eastward and westward from the magnetic field line resembling a C-shape and reversed C-shape structures. These EPBs were inside the GOLD imager’s field-of-view for a period of ~3 hours. This allowed us to compute their zonal motion and determine their drift velocities. EPBs’ drift velocities were derived from measuring their longitudinal shifts at the magnetic equator and at both EIA crests. This unique observation, showing three morphologies in a narrow longitude sector, indicates the occurrence of strong longitudinal gradients in the typical parameters associated with the dynamics of EPBs, like neutral winds, electric fields, or other parameters within such a narrow longitude range.

The nighttime ionospheric response to a geomagnetic storm occurred on 23-29 September 2020 is investigated over the South American, Atlantic, and West African longitude sectors using NASA’s Global-scale Observations of the Limb and Disk (GOLD) measurements. On 27 September the solar wind conditions were favorable for prompt penetration electric fields (PPEF) to influence the equatorial ionosphere over extended longitudes. The equatorial ionization anomaly (EIA) crests were shifted 8o-10o poleward compared to the quiet time monthly mean across ~65o- 35oW during the main phase. Ionosonde hmF2 (peak electron density height) measurements from Fortaleza (GG: -3.9oN and -38.4oW) indicated a stronger prereversal enhancement this evening than other nights. As a result, Equatorial Plasma Bubbles (EPB) occurred at these longitudes on this evening. This is the first simultaneous investigation of EIA morphology and EPB occurrence rate over an extended longitude range from geostationary orbit during a geomagnetic storm.

Observations of far-ultraviolet (FUV) dayglow by the Global-scale Observations of Limb and Disk (GOLD) mission provide a new opportunity to monitor relative composition changes in the upper atmosphere as well as solar extreme ultraviolet (EUV) variability. Relative composition changes are quantified by ΣO/N2, the column density ratio of atomic oxygen to molecular nitrogen, while QEUV provides a measure of the solar EUV energy flux from 1 to 45 nm into the upper atmosphere. This spectral range provides the ionizing radiation which ultimately results in FUV airglow emission produced by photodissociation and photoelectron impact. The quantities ΣO/N2 and QEUV are derived from GOLD FUV observations through lookup tables that are constructed using a first-principles photoelectron transport model. The two FUV emissions used are O I 135.6 nm and the N2 Lyman-Birge-Hopfield (LBH) bands. We present an overview of the theoretical basis for the algorithms and practical considerations for application to GOLD data. The effects of uncertainties in electron impact cross sections, off-nadir viewing, and instrument artifacts are reviewed. We also discuss GOLD Level 1C DAY, Level 2 data products ON2 and QEUV, and present representative samples of each.

Global-scale Observations of Limb and Disk (GOLD) disk measurements of far ultraviolet molecular nitrogen band emissions are used to retrieve column integrated disk temperatures (Tdisk), which are representative of the lower-and-middle thermosphere. The present work develops a new approach to assimilate the Tdisk in the Whole Atmosphere Community Climate Model with thermosphereâ\euro?ionosphere eXtension (WACCMX) using the Data Assimilation Research Testbed (DART) ensemble adjustment Kalman filter. Nine days of data,1 to 9 November 2018, are assimilated. Analysis state variables such as thermospheric effective temperature (Teff, airglow layer integrated temperature), ratio of atomic oxygen to molecular nitrogen column densities (O/N2), and column electron content are compared with a control simulation that is only constrained up to ~50 km. It is observed that assimilation of the GOLD Tdisk improves the analysis states when compared with the control simulation. The analysis and model states, particularly, Teff, O/N2, and Electron Column Density (ECD) are also compared with their measurement counterparts for a validation of the assimilation. Teff and O/N2 are compared with GOLD Tdisk and O/N2. While, the ECD is compared with ground based Total Electron Content (TEC) measurements from Global Navigational Satellite System (GNSS) receivers. Root Mean Square Error (RMSE) improvements in Teff and O/N2 are about 10.8% and 22.6%, respectively. The RMSE improvement in analyses ECD is about 10% compared to control simulation.