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Abstract The Global‐scale Observations of Limb and Disk (GOLD) mission has provided an unusual array of upper atmosphere observations from a geostationary platform, including the behavior of the low latitude nighttime ionosphere. One of the features observed by GOLD is the formation of an X‐pattern in the Equatorial Ionization Anomaly when its crests collapse near the magnetic equator. This paper discusses the X‐patterns that were observed during the first 5 years of the GOLD mission (2018–2023). This catalog reveals that X‐pattern occurrences are more frequent during low solar activity, and appear to be driven by changes in the normal low latitude zonal winds. In the longitude region observed by GOLD (approximately 75°W–5°E) they occurred exclusively during the September Equinox‐December Solstice‐March Equinox seasons, and they were more likely to occur near 45°W longitude, near the point where the geomagnetic equator crosses the geographic equator in the western hemisphere. 

Abstract Horizontals drifts of equatorial Spread F (ESF) at post-sunset and post-midnight are investigated by analyzing six ESF events observed during the period of November 2022–March 2023. Horizontal drift velocities of ESFs are calculated from the time lags between signals recorded by different transmitter–receiver pairs of a new Continuous Doppler Sounding (CDS) system operating at 6.80 MHz in a low latitude station, Tucumán, Argentina (26° 49’ S, 65° 13' W, mag. latitude ~ 13°) and by the older CDS system working at 4.63 MHz. A new method of time lags determination for spread structures is presented. In addition, the occurrence of airglow depletions associated with ESF events is verified using images of airglow emissions of atomic O red line, 630 nm. We found that the typical speeds of the ESF drift in the post-sunset hours (around 130 m/s) are about two times greater than the speeds of ESF occurring around midnight or in post-midnight hours (around 80 m/s). The drift speeds obtained using 4.63 and 6.80 MHz systems were practically the same with the exception of one event, which might have been due to wind shear. Azimuths obtained by 4.63 and 6.80 MHz systems are almost similar. No systematic dependence of the azimuth on the local time and sounding frequency was found. All ESF events drift roughly eastward with an average azimuth of about 105$$^\circ$$ $_{}^{\circ }$with respect to the geographic north. Graphical Abstract 

Abstract 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 and 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. 

Abstract Low‐cost instrumentation combined with volunteering and citizen science educational initiatives allowed the deployment of L‐band scintillation monitors to remote sense areas that are geomagnetically conjugated and located at low‐to‐mid latitudes in the American sector (Quebradillas in Puerto Rico and Santa Maria in Brazil). On 10 and 11 October, 2023, both monitors detected severe scintillations, some reaching dip latitudes beyond 26°N. The observations show conjugacy in the spatio‐temporal evolution of the scintillation‐causing irregularities. With the aid of collocated all‐sky airglow imager observations, it was shown that the observed scintillation event was caused by extreme equatorial plasma bubbles (EPBs) reaching geomagnetic apex altitudes exceeding 2,200 km. The observations suggest that geomagnetic conjugate large‐scale structures produced conditions for the development of intermediate scale (few 100 s of meters) in both hemispheres, leading to scintillation at conjugate locations. Finally, unlike previous reports, it is shown that the extreme EPBs‐driven scintillation reported here developed under geomagnetically quiet conditions. 

Abstract A coronal mass ejection erupted from the Sun on 21 April 2023 and created a G4 geomagnetic storm on 23 April. NASA's global‐scale observations of the limb and disk (GOLD) imager observed bright equatorial ionization anomaly (EIA) crests at ∼25° Mlat, ∼11° poleward from their average locations, computed by averaging the EIA crests during the previous geomagnetic quiet days (18–22 April) between ∼15°W and 5°W Glon. ReversedC‐shape equatorial plasma bubbles (EPBs) were observed reaching ∼±36° Mlat (∼40°N and ∼30°S Glat) with apex altitudes ∼4,000 km and large westward tilts of ∼52°. Using GOLD's observations EPBs zonal motions are derived. It is observed that the EPBs zonal velocities are eastward near the equator and westward at mid‐latitudes. Model‐predicted prompt penetration electric fields indicate that they may have affected the postsunset pre‐reversal enhancement at equatorial latitudes. Zonal ion drifts from a defense meteorological satellite program satellite suggest that westward neutral winds and perturbed westward ion drifts over mid‐latitudes contributed to the observed latitudinal shear in zonal drifts. 

Abstract During the 17 March 2015 geomagnetic storm, citizen scientist observations from Dunedin (45.95°S, 170.32°E), New Zealand, revealed a bright wide red arc known as stable auroral red (SAR) arc evolving into a thin white‐mauve arc, known as Strong Thermal Emission Velocity Enhancement (STEVE). An all‐sky imager at the Mount John Observatory (43.99°S, 170.46°E), 200 km north of Dunedin, detected an extremely bright arc in 630.0 nm, with a peak of ∼6 kR, colocated with the arc measured at Dunedin at an assumed height of 425 km. Swarm satellite data measured plasma parameters that showed strong subauroral ion drift signatures when the SAR arc was observed. These conditions intensified to extremely high values in a thinner channel when STEVE was present. Our results highlight the fast evolution of plasma properties and their effects on optical emissions. Current theories and models are unable to reproduce or explain these observations. 

Abstract We utilized citizen scientist photographs of subauroral emissions in the upper atmosphere and identified a repeatable sequence of proton aurora and subauroral red (SAR) arc during substorms. The sequence started with a pair of green diffuse emissions and a red arc that drifted equatorward during the substorm expansion phase. Simultaneous spectrograph and satellite observations showed that they were subauroral proton aurora, where ion precipitation created secondary electrons that illuminated aurora in green and red colors. The ray structures in the red arc also indicated existence of low‐energy electron precipitation. The green diffuse aurora then decayed but the red arc (SAR arc) continued to move equatorward during the substorm recovery phase. This sequence suggests that the SAR arc was first generated by secondary electrons associated with ion precipitation and may then transition to heat flux or Joule heating. Proton aurora provides observational evidence that ion injection to the inner magnetosphere is the energy source for the initiation of the SAR arc. 

Abstract Evolution of large‐scale and fine‐scale plasmaspheric plume density structures was examined using space‐ground coordinated observations of a plume during the 7–8 September 2015 storm. The large‐scale plasmaspheric plume density at Van Allen Probes A was roughly proportional to the total electron content (TEC) along the satellite footprint, indicating that TEC distribution represents the large‐scale plume density distribution in the magnetosphere. The plasmaspheric plume contained fine‐scale density structures and subauroral polarization streams (SAPS) velocity fluctuations. High‐resolution TEC data support the interpretation that the fine‐scale plume structures were blobs with ∼300 km size and ∼500–800 m/s in the ionosphere (∼3,000 km size and ∼5–8 km/s speed in the magnetosphere), emerging at the plume base and drifting to the plume. The short‐baseline Global Navigation Satellite System receivers detected smaller‐scale (∼10 km in the ionosphere, ∼100 km in the magnetosphere) TEC gradients and their sunward drift. Fine‐scale density structures were associated with enhanced phase scintillation index. Velocity fluctuations were found to be spatial structures of fine‐scale SAPS flows that drifted sunward with density irregularities down to ∼10 s of meter‐scale. Fine‐scale density structures followed a power law with a slope of ∼−5/3, and smaller‐scale density structures developed slower than the larger‐scale structures. We suggest that turbulent SAPS flows created fine‐scale density structures and their cascading to smaller scales. We also found that the plume fine‐scale density structures were associated with whistler‐mode intensity modulation, and localized electron precipitation in the plume. Structured precipitation in the plume may contribute to ionospheric heating, SAPS velocity reduction, and conductance enhancements. 

Abstract. The 10 May 2024 geomagnetic storm, referred to as the Gannon Storm in this paper, was one of the most extreme to have occurred in over 20 years. In the era of smartphones and social media, millions of people from all around the world were alerted to the possibility of exceptional auroral displays. Hence, many people not only witnessed but also photographed the aurora during this event. These citizen science observations, although not from scientific instruments operated by observatories or research groups, can prove to be invaluable in obtaining data to characterise this extraordinary event. In particular, many observers saw and photographed the aurora at mid-latitudes, where ground-based instruments targeting auroral studies are sparse or absent. Moreover, the proximity of the event to the Northern Hemisphere summer solstice meant that many optical instruments were not in operation due to the lack of suitably dark conditions. We created an online survey and circulated it within networks of aurora photographers to collect observations of the aurora and of disruptions in technological systems that were experienced during this superstorm. We obtained 696 citizen science reports from over 30 countries, containing information such as the time and location of aurora sightings and the observed colours and auroral forms, as well as geolocalisation, network, and power disruptions noticed during the geomagnetic storm. We supplemented the obtained dataset with 186 auroral observations logged in the Skywarden catalogue (https://taivaanvahti.fi, last access: 19 December 2024) by citizen scientists. The main findings enabled by the data collected through these reports are that the aurora was widely seen from locations at geomagnetic latitudes ranging between 30 and 60°, with a few reports from even lower latitudes. This was significantly further equatorward than predicted by auroral oval models. The reported auroral emission colours, predominantly red and pink and intense enough to reach naked-eye visibility, suggest that the auroral electron precipitation contained large fluxes of low-energy (< 1 keV) particles. This study also reveals the limitations of citizen science data collection via a rudimentary online form. We discuss possible solutions to enable more detailed and quantitative studies of extreme geomagnetic events with citizen science in the future. 

Equatorial Plasma Bubbles (EPBs) are a region of depleted ionospheric densities. EPBs are known to fluctuate both seasonally and day to day, and have been linked to changes in solar activity, geomagnetic activity, and seeding resulting from dynamics occurring at lower altitudes. Here, EPB activity is investigated over a 15-day period with overlapping coincident ground-based 630 nm oxygen airglow measurements, near-infrared hydroxyl mesospheric temperature mapper (MTM) measurements, and Rate Of change of Total Electron Content Index (ROTI) values. The data are compared with the Navy Global Environmental Model (NAVGEM) reanalysis over the same time period. It is found that several days with strong EPB activity coincided with the positive/northward meridional wind phase of the quasi-two-day wave (QTDW) in the mesosphere. These initial observations indicate correlations of the QTDW phase and the occurrence rates of EPBs, and suggest a need for further investigations to assess potential causal relationships that may affect the variability and prevalence of EPBs.