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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. Plain Language Summary On Earth's nightside during the super geomagnetic storm that occurred on 10 May 2024, NASA's GOLD imager saw something new: a part of Earth's ionosphere, the southern peak of what typically appears as a double‐peaked structure in the ionospheric density at equatorial and low latitudes, merged with the aurora near the southern tip of South America. This has never been reported before. Additionally, the boundary of the aurora expanded further equatorward than usual. These observations of what happened in the Earth's ionosphere during this super storm are reported for the first time in this study. Key Points EIA crests between ∼70° and 35°W moved poleward, with northern and southern crest reaching ∼38°N and ∼35°S Mlat in the American sector Southern EIA crest moved poleward with a speed of ∼450 m/s near ∼55°W Glon during strong IMF Bz and d(Dst)/dt First observation of the merging of an EIA crest with the aurora indicating no mid‐latitude ionosphere

One of the most intense geomagnetic storms of recent times occurred on 10–11 May 2024. With a peak negative excursion of Sym‐H below −500 nT, this storm is the second largest of the space era. Solar wind energy transferred through radiation and mass coupling affected the entire Geospace. Our study revealed that the dayside magnetopause was compressed below the geostationary orbit (6.6 RE) for continuously ∼6 hr due to strong Solar Wind Dynamic Pressure (SWDP). Tremendous compression pushed the bow‐shock also to below the geostationary orbit for a few minutes. Magnetohydrodynamic models suggest that the magnetopause location could be as low as 3.3RE. We show that a unique combination of high SWDP (≥15 nPa) with an intense eastward interplanetary electric field (IEFY ≥ 2.5 mV/m) within a super‐dense Interplanetary Coronal Mass Ejection lasted for 409 min–is the key factor that led to the strong ring current at much closer to the Earth causing such an intense storm. Severe electrodynamic disturbances led to a strong positive ionospheric storm with more than 100% increase in dayside ionospheric Total Electron Content (TEC), affecting GPS positioning/navigation. Further, an HF radio blackout was found to occur in the 2–12 MHz frequency band due to strong D‐ and E‐region ionization resulting from a solar flare prior to this storm.

This study utilizes ICON/MIGHTI observations and reveals, for the first time, the response of neutral temperature in the lower thermosphere (∼110–130 km) to minor‐to‐moderate geomagnetic disturbances. A case study of the 12 October 2021 storm reveals surprising storm‐time temperature enhancements across all observed latitudes (∼14°–42°N), with a peak enhancement of 28% at 130 km near 42°N. The average enhancement within 35°–40°N reaches 18% at 130 km. Statistical analysis indicates a positive correlation between temperature enhancement and geomagnetic activity intensity. The increase rates with respect to ap index are larger in 35°–40°N than those in 20°–25°N. The increase rates increase with altitude, reaching 0.168%/nT at 130 km over 35°–40°N. The peaks of temperature enhancements lag the ap/Dst index maxima/minima for most storms. Comparisons with the NRLMSIS2.1 empirical model and the physics‐based TIEGCM‐ICON model show that both models capture storm‐time temperature enhancements but underestimate their magnitudes compared to observations.

Geomagnetic storms affect Earth in various severe ways, including damaging satellites, disrupting power grids, and inducing prompt penetration electric fields (PPEF) through Joule heating in the auroral region. They also cause disturbance dynamo electric fields (DDEF), generate or suppress equatorial plasma bubbles (EPBs), and lead to other significant effects. The extreme geomagnetic storm on 10 May 2024, altered the dynamics of the ionosphere. The ionospheric response was investigated in this study. Our methodology utilized a combined data set, including GNSS receivers in the Latin American sector, and data from ionosondes in São Luis (SALU) and Cachoeira Paulista (CHPI). CHPI also features a Fabry‐Pérot interferometer (FPI) and an All‐Sky Imager (ASI). Super EPB was observed in the American sector. This structure drifted westward at a velocity of ∼140 m/s and had a large latitudinal extension, reaching about 36° geomagnetic latitude, this corresponds to an apex height of around 4,500 km. The depletion lasted for a long duration of 12 hr, from 22:30 to 10:30 UT. The geomagnetic storm caused a super fountain effect, propelling plasma from the equator to a distance of ∼35° latitude, and depositing high‐density plasma on the crest of the equatorial ionization anomaly (EIA).

The Asian sector is reported to have experienced a strong electron density enhancement during the May 2024 super geomagnetic storm between local evening and sunrise. We present a high‐resolution 3‐D ionospheric reconstructions over Japan using computerized ionospheric tomography (CIT) facilitated by a dense Global Navigation Satellite System (GNSS) network. Results reveals storm‐enhanced density (SED) features characterized by increases in total electron content (TEC) and F2‐layer peak density (NmF2), elevated height (hmF2), and increased electron densities at higher altitudes. Spatially, the SED structures extended ∼${\\sim} $ 1,000 km latitudinally and 300 km vertically. Within these enhancements, large‐scale electron density depletions, spanning over 600 km and aligned with geomagnetic field lines, were identified. We hypothesize these depletions as equatorial plasma bubbles (EPBs) that extend into mid‐latitudes while remaining embedded in the SED. These results, highlight the capability of GNSS‐based 3‐D CIT in extending a quantitative understanding of complex ionospheric features during extreme events.

The high latitude ionospheric evolution of the May 10‐11, 2024, geomagnetic storm is investigated in terms of Total Electron Content and contextualized with Incoherent Scatter Radar and ionosonde observations. Substantial plasma lifting is observed within the initial Storm Enhanced Density plume with ionospheric peak heights increasing by 150–300 km, reaching levels of up to 630 km. Scintillation is observed within the cusp during the initial expansion phase of the storm, spreading across the auroral oval thereafter. Patch transport into the polar cap produces broad regions of scintillation that are rapidly cleared from the region after a strong Interplanetary Magnetic Field reversal at 2230UT. Strong heating and composition changes result in the complete absence of the F2‐layer on the eleventh, suffocating high latitude convection from dense plasma necessary for Tongue of Ionization and patch formation, ultimately resulting in a suppression of polar cap scintillation on the eleventh. Plain Language Summary The intense geomagnetic storm of May 2024 caused a plethora of different responses within the Earth's ionosphere. In the early phases of the storm, the auroral oval quickly expands to upper midlatitudes and induces strong variations in Global Navigation Satellite System (GNSS) phase measurements. Concurrently, midlatitude plasma is repeatedly lifted by 100–300 km on timescales of about an hour resulting in enhanced plasma densities. This intensified and lifted plasma is then drawn into the polar cap inducing variations in GNSS amplitude and phase. As the storm evolves, heating drives mixing of the thermosphere and causes an extreme depletion in ionospheric plasma. After 24 hr, despite severe geomagnetic conditions persisting, the depleted plasma environment results in only relatively weak plasma transport into the polar cap and significantly reduced impacts on GNSS. Key Points Plasma lifting during the storm caused midlatitude displacements of ionospheric peak height by as much as 300 km over the course of 1 hour Sporadic‐E is observed at the sub‐auroral convective boundary edge of the storm‐enhanced density with strong plasma drift shears present Severe depletion of electron density at mid and high latitudes significantly reduced the impact of subsequent geomagnetic activity on GNSS

The Community Earth System Model (CESM) Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (WACCM‐X) is used to investigate how the ionosphere‐thermosphere response to a May 2024‐like geomagnetic storm changes with increasing greenhouse gases. Coupled CESM(WACCM‐X) simulations are first performed following the Coupled Model Intercomparison Project Phase 6 Shared Socioeconomic Pathway 5–8.5 from 2000 to 2090. The May 2024 geomagnetic superstorm is then simulated in 2016, 2040, 2061, and 2084, corresponding to surface CO2${\\text{CO}}_{2}$levels of 403, 500, 652, and 918 ppmv, respectively. The CESM(WACCM‐X) simulations indicate that increasing levels of CO2${\\text{CO}}_{2}$weakens the absolute neutral density response at 350 km. However, the relative response is increased with increasing levels of CO2${\\text{CO}}_{2}$ , which is partly due to the decrease in the background neutral density. Due to a weaker response in thermosphere composition and meridional neutral winds, the ionospheric response in absolute terms also weakens with increasing levels of CO2${\\text{CO}}_{2}$ .

Earth experienced the strongest geomagnetic storm in 20 years over 10–13 May 2024. The Ap and Dst geomagnetic indices were 273 and −291.94 nT on 11 May. The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite observed significant enhancement in thermospheric infrared emission at 15, 5.3, 4.3, and 1.27 μm. On 11 May the daily global power radiated by nitric oxide (NO) at 5.3 μm was 1.41 TW and by carbon dioxide (CO2) at 15 μm was 1.35 TW. These are the largest single day power values observed by SABER in 22 years and the first time the daily power radiated by NO exceeded that of CO2. The total infrared power (above background) radiated during the storm was 2.64 TW (2.28 × 1017 J). Significant enhancement in limb radiance observed at 4.3 μm (to 250 km tangent height) is likely indicative of NO + formation during the storm. Plain Language Summary The layer of Earth's atmosphere above 100 km is referred to as the “thermosphere” and can be thought of as the boundary between the space environment above it and the atmosphere below it. In early May 2024, an active sunspot ejected a significant amount of charged particles (protons and electrons) within a strong magnetic field toward Earth. This “coronal mass ejection” or CME encountered Earth's high atmosphere 10–13 May, causing a significant “geomagnetic storm” that significantly heated the thermosphere and modified its chemical composition. The effects of this storm were observed by the SABER instrument which is flying on the NASA Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) observes infrared light emitted by carbon dioxide, nitric oxide, molecular oxygen, and ionized nitric oxide produced during the storm. The 10–13 May storm caused the global average infrared radiation levels to increase by nearly a factor of 10 at some wavelengths in 1 day. The storm and the infrared radiation levels dissipated back to pre‐storm levels over the next 2 days. This storm was the third strongest in terms the power (2.64 trillion watts) radiated by the thermosphere in the past 22 years observed by SABER. The observed enhancements in infrared radiation at multiple wavelengths offer the opportunity to more fully understand how the Sun interacts with and influences Earth's highest atmosphere. Key Points The daily Ap (273 nT) and Dst (−291.94 nT) indexes on 11 May 2024 were the largest since the launch of the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics (TIMED) satellite in December 2001 The power radiated 11 May by NO and CO2 exceeded 1 TW each and the NO power (1.41 TW) exceeded the CO2 power (1.35 TW) for the first time Total storm radiated power, above background, is 2.64 TW (2.28 × 1017 J), making it the third strongest storm during the TIMED era

It has long been a mystery why small Total Solar Irradiation changes have significant effects on Earth's climate. Solar cycle correlation studies abound but cannot conclusively point to a viable physical mechanism. Here, I show that geomagnetic storms have a profound terrestrial weather impact. Using 67 years of hourly Disturbance storm time (Dst) index and ERA5 atmosphere data over North America, I find geomagnetic storm impacts up to two orders of magnitude larger than the long‐term global mean surface temperature impact attributed to solar activity. Particle precipitation effects such as from cosmic rays, solar energetic particles, or magnetospheric electrons are least consistent with my results. In particular, the cosmic ray–cloudiness hypothesis is falsified by my results. A top‐down mechanism operating directly through the ionosphere or through stratospheric chemistry and the polar vortex appears to be more likely.

Understanding the effects of east‐west component of interplanetary magnetic field (IMF‐By) on the equatorial ionospheric electrodynamics is challenging due to the complex response caused by the simultaneous occurrence of multiple mechanisms during disturbed times. The extreme geomagnetic storm on 10 May 2024 caused by multiple‐ICME interactions accompanied with unprecedented IMF‐By magnitudes and its polarity, changed from west to east by 130 nT during northward IMF‐Bz turning. The ground ionosonde observations of h’F from near‐equatorial locations, along with the latitudinal profiles of plasma densities from Swarm satellites reveal the first observational evidence of the impact of strong IMF‐By near the dusk‐terminator (17–19.5 LT), causing strong dawn‐to‐dusk ionospheric electric fields during northward IMF‐Bz. This electric field produces large uplift of the ionospheric plasma near equator and subsequent super‐fountain effect near the dusk. The combined effect of increased IMF‐By amplitudes and viscous terms might have resulted into the enhanced coupling of solar wind with the magnetosphere. Plain Language Summary The southward component of interplanetary magnetic field (IMF‐Bz) is a primary driver for the solar wind‐magnetosphere coupling, which produces geomagnetic disturbances on the Earth. Whereas east‐west component of IMF (IMF‐By) can modify the effects of these disturbances. Understanding the effects of IMF‐By on the equatorial ionosphere is challenging due to the complex response caused by the simultaneous occurrence of multiple mechanisms during disturbed times, such as ring current, prompt penetration and disturbance dynamo electric fields etc. During the extreme geomagnetic storm which occurred on 10 May 2024, the IMF‐By component was very intense. Both, Bz and By components of IMF made sudden and giant transitions, changing their orientation rapidly. We have investigated the effects of this rarest event on the equatorial ionospheric electric fields. We find penetration of strong eastward electric field near dusk during northward and eastward IMF conditions. Key Points Unprecedented IMF‐By amplitudes during northward IMF show strong eastward ionospheric electric fields at dusk near equator The effects are strongest near dusk and overshielding effects are evident near noon First observational evidence of the impact of strong IMF‐By on the equatorial ionosphere near dusk