Editorial: Impacts of the Extreme Gannon Geomagnetic Storm of May 2024 throughout the Magnetosphere-Ionosphere-Thermosphere System

Denny Oliveira^1*Mirko Piersanti²Maria-Theresia Walach³Lívia R. Alves⁴W Kent Tobiska⁵Xochitl Blanco-Cano⁶Katariina Nykyri⁷

• ¹University of Maryland, Baltimore County, Baltimore, United States
• ²Universita degli Studi dell'Aquila, L'Aquila, Italy
• ³Lancaster University, Lancaster, United Kingdom
• ⁴Instituto Nacional de Pesquisas Espaciais, Sao Jose dos Campos, Brazil
• ⁵Space Environment Technologies, Los Angeles, United States
• ⁶Universidad Nacional Autonoma de Mexico, Mexico City, Mexico
• ⁷Embry-Riddle Aeronautical University, Daytona Beach, United States

of large coronal mass ejections (CMEs) emanating from a highly active sunspot region, unleashing several X-class solar flares into the interplanetary space. Figure 1 (Li et al., 2025) and elevating high-altitude radiation exposure (Hayakawa et al., 2025;Papaioannou et al., 2025).The multiple CMEs interacted and merged en-route to Earth, resulting in a complex ejecta structure that compressed the magnetosphere (magnetopause standoff position to ∼5 Earth radii) and triggered the largest storm in the past two decades (minimum Dst ∼ -406 nT). The solar and geomagnetic effects of the 2024), who showed that extremely high solar wind dynamic pressure strongly compressed the magnetosphere. This compression intensified the magnetopause current, the dawn-dusk interplanetary electric field, large sudden impulses, and rapid magnetic field variations observed on the ground (Piersanti et al., 2025). The enhanced pressure also increased solar wind-magnetosphere coupling, strengthening the auroral electrojets and expanding auroral activity to unusually low latitudes (Nilam et al., 2025). Overall, the elevated dynamic pressure was a major factor amplifying the geomagnetic disturbances and ground impacts during the May 2024 storm (Tulasi Ram et al., 2024).Many space weather and geomagnetic effects have been reported for this storm. This includes the generation of very large Kelvin-Helmholtz waves at the CME ejecta-sheath boundaries upstream of the Earth (Nykyri, 2024), low-latitude auroras (Hayakawa et al., 2025), the largest geomagnetically induced current (GIC) peak ever observed in Latin America (Caraballo et al., 2025), positioning outrages of Global Positioning System (GPS) due to ionospheric disturbances (Yang and Morton, 2025), caused the largest upward satellite migration ever performed in low-Earth orbit (LEO) (Parker and Linares, 2024), and accelerated satellite re-entry from LEO with respect to a reference altitude ∼ 280 km (Oliveira et al., 2025a). This Research Topic received 6 articles dealing with different aspects of elevated radiation levels and geomagnetic activity in May 2024. The findings reported in these articles are briefly summarized below.We begin this editorial with the topic of aviation radiation effects. Tobiska et al. evaluate how aviation radiation mitigation strategies performed during the extreme Gannon storm due to high solar activity. The authors compare real-time radiation monitoring and mitigation tools at flight altitudes, demonstrating that the established ALARA (as low as reasonably achievable) frameworks successfully limited exposure even as SEP fluxes and atmospheric dose rates surged. Their findings highlight the importance of robust, validated aviation-radiation procedures during extreme space weather events. Such mitigation actions correspond to lowering altitudes and route deviations to equator-ward magnetic latitudes due to magnetic shielding effects (Gao et al., 2022), reinforcing that terrestrial infrastructure and high-altitude aviation are vulnerable -and yet that mitigation protocols can work effectively under extreme conditions.Addressing the same topic of aviation radiation, Schennetten et al. used a physics-based radiation transport and dose-calculation model to simulate radiation dose rates at aviation altitudes and LEO, combining three distinct contributions: 1) the additional dose from SEPs; 2) changes in geomagnetic shielding (cut-off rigidities) evaluated during the storm; and 3) the effect of a Forbush decrease reducing the galactic cosmic ray background. Using this approach, Schennetten et al. found that although the SEPs during the Gannon storm did contribute to the radiation field at aviation altitudes, but the dose rates remained relatively low. However, dose rates in LEO reached much higher values. Moreover, when all effects are combined for a hypothetical flight from Frankfurt to Los Angeles, the additional total effective dose was estimated at 14%-24% above baseline. The study thereby highlights that while SEPs can elevate doses during an extreme storm, this is not necessarily the case for every such event, because the actual impact depends strongly on the SEP energy spectrum, geomagnetic conditions, and atmospheric shielding.Using data from the SuperMAG ground network, the Spherical Elementary Current System method -which maps ionospheric currents -and mid-latitude auroral imagery, Ngwira et al. examine ground geomagnetic activity during the Gannon storm. Those authors show that powerful CME-CME interactions and prolonged southward interplanetary magnetic field (IMF) B z drove exceptionally strong magnetic perturbations -up to 700 nT and >500 nT/min at mid-latitudes across the United States. The auroral oval expanded equatorward to 40 • -45 • magnetic latitude, producing vivid aurorae and intense substorm activity far from the polar regions in the American sector (Gonzalez-Esparza et al., 2024;Hayakawa et al., 2025).The results reveal how extreme IMF conditions and abrupt B y rotations can trigger westward-propagating auroral electrojets that enhance ground-level magnetic variations, underscoring the vulnerability of midlatitude infrastructure to space weather hazards once thought confined to high latitudes.Lawrence et al. present both direct ground magnetic and electric field observations across the UK and combine these with magnetotelluric-derived resistivity models of the subsurface and a high-voltage transmission network model to estimate GICs. The key findings include the auroral electrojet intrusion to surprisingly low latitudes (below ∼54 • N) across central and southern England, rapid and large ground magnetic field changes (minute-to-minute magnetic field variations) and estimated substation GICs exceeding ∼60 A in parts of southwest and east-central England and northern Wales. As a result, Lawrence et al. show that the integration of multi-site geoelectric modeling, grid-network simulation and magnetic observations offers a comprehensive assessment of ground-impact risks during extreme space weather and highlights the need for region-specific vulnerability analyses.Da Silva et al. combine multi-instrument satellite and ground-based observations to investigate how the Gannon storm affected the South Atlantic Magnetic Anomaly (SAMA), a region with the weakest geomagnetic field (Gledhill, 1976). Using particle detectors aboard LEO satellites, Da Silva et al. monitored the behavior of low-energy electrons in the inner radiation belt, while ionospheric radars and digisondes provided measurements of ionization changes over South America. In addition, satellite-borne sensors tracked variations in ozone concentration in the upper atmosphere. The study found that the flux of low-energy electrons in the inner radiation belt vanished at the same time that energy input into the magnetosphere ceased -indicating a strong coupling between these processes. This period coincided with enhanced ionization in the ionospheric E-region over SAMA and pronounced variability in electron fluxes.Finally, Yuan et al. used coordinated lidar and optical observations from a midlatitude station to reveal how the neutral atmosphere responded to the Gannon storm. Their analysis show that during the storm, the upper portion of the sodium layer nearly disappeared at the same time that thermospheric temperatures increased and strong equatorward winds developed. These simultaneous changes indicate that energy and momentum from high-latitude geomagnetic activity penetrated deeply into midlatitudes, directly altering both the dynamics and composition of the mesosphere and lower thermosphere. The results demonstrate that even regions far from the auroral zones can experience significant coupling between magnetospheric forcing, neutral winds, and atmospheric chemistry during extreme space weather events. The right panel of Figure 1 presents a schematic diagram highlighting the key regions and technological systems affected by space weather, along with the first author associated with each contributing study.In summary, this Research Topic enhances our understanding of solar and geomagnetic effects during the May 2024 storm on aviation radiation, GICs and geoelectric fields in the US and the UK, effects on the atmosphere at mid-latitude mesosphere and lower thermosphere, and perturbations in the neutral and ionized atmosphere over the SAMA region. Although our focus was on the Gannon storm, the October 2024 storm can also offer further insights of extreme space weather effects. Even though the October event was the third extreme event since the Halloween storms of 2003 (Oliveira et al., 2025b), very few studies have focused on that event thus far. Examples are intense red aurora observations by citizen scientists (Kataoka et al., 2025), impacts of merging electric field on field-aligned currents and polar electrojets (Xia et al., 2025), and a premature re-entry of a Starlink satellite (Oliveira et al., 2025b). Studies comparing many aspects of the extreme 2024 events -including their drivers and subsequent space weather effectscould be the focus of a future Rearch Topic in Frontiers in Astronomy and Space Sciences.Jennifer L. Gannon was a distinguished space-weather scientist whose research profoundly advanced our understanding of GICs and ground-magnetic disturbances (Lugaz et al., 2024). Dr. Gannon's work established essential connections between magnetospheric physics and the protection of technological infrastructure on Earth. The extreme geomagnetic storm of May 2024, now known as the Gannon storm and the topic of this editorial, fittingly honors her enduring contributions and impact on the geospace community. We dedicate this editorial and Research Topic to the memory of Dr. Gannon.