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Geomagnetism
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Channell, J. E. T., & Vigliotti, L. (2019). The role of geomagnetic field intensity in Late Quaternary evolution of humans and large mammals. Reviews of Geophysics. 57, 709–738. https://doi.org/10.1029/2018RG000629
Plain Language Summary
The strength of Earth's magnetic field in the past, recorded by rocks and sediments, provides a proxy for past flux of ultraviolet radiation (UVR) to Earth's surface due to the role of the field in modulating stratigraphic ozone. About 40,000 years ago, mammalian fossils in Australia and Eurasia record an important die-off of large mammals that included Neanderthals in Europe. In the Americas and Europe, a large mammalian die-off appears to have occurred ~13,000 years ago. Both die-offs can be linked to minima in Earth's magnetic field strength implying that UVR flux variations to Earth's surface influenced mammalian evolution. For the last ~200,000 years, estimates of the timing of branching episodes in the human evolutionary tree, from modern and fossil DNA and Y chromosomes, can be linked to minima in field strength, which implies a long-term role for UVR in human evolution. New fossil finds, improved fossil dating, knowledge of the past strength of Earth's magnetic field, and refinements in the human evolutionary tree, are sharpening the focus on a possible link between UVR arriving at the Earth's surface, magnetic field strength, and events in mammalian evolution.
Chulliat, A., Nair, M. & Califf, S. Candidate geomagnetic field models for IGRF-14 and secular acceleration since 2020. Earth Planets Space 78, 26 (2026). https://doi.org/10.1186/s40623-025-02362-y
Abstract
IGRF-14 is the fourteenth generation of the International Geomagnetic Reference Field (IGRF), a spherical harmonic model of Earth’s main magnetic field and its secular variation, developed through international collaboration under the auspices of the International Association of Geomagnetism and Aeronomy (IAGA). This paper describes the development, in October 2024, of candidate main field (MF) models at epochs 2020.0 and 2025.0, and a secular variation (SV) model at 2025.0, derived from Swarm satellite data, as well as the validation of the SV model using ground-based observatory measurements. Swarm data collected through May 2025 were subsequently used to update the continuous parent model from which these candidates were derived, which now spans 2014.42 to 2024.92. This model is used to conduct a retrospective assessment of SV performance and to analyze recent secular acceleration (SA) signals. Our results reveal a pronounced SA pulse centered in 2022 and provide evidence for a geomagnetic jerk in 2024, confirmed by recent observatory data from Western Europe and North America. These rapid, nonlinear core field changes have already contributed to the early degradation of the IGRF-14 SV forecast, underscoring the challenges of modeling geomagnetic field evolution and the importance of continuous satellite and ground-based observations.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Hugo G. Nami New Paleomagnetic results and evidence for a geomagnetic field excursion during the pleistocene-holocene transition at Pichincha province, Ecuador Geofísica Internacional Volume 54, Issue 2, April–June 2015, Pages 127-148 https://doi.org/10.1016/j.gi.2015.04.009
Abstract
Paleomagnetic data from three sedimentary sections in Pichincha province -Quito City (QC), Mullimica (Mu) and El Tingo (ET)- Ecuador (northwestern South America) are reported. Analysis of natural remanent magnetization directions obtained from 109 oriented samples taken at 4 sites, shows that some samples recorded a magnetic component different from the normal present geomagnetic field (GMF). The characteristic remanent magnetization (ChRM) was determined by progressive AF demagnetization. The analysis shows that the sections recorded ChRM of normal, intermediate and reverse polarities during the Pleistocene-Holocene transition and Holocene. Normal directions were recorded in QC, while normal and intermediate polarity directions at Mu and, reverse VGPs at ET. QC and the upper portion of Mu correspond to the paleosecular variation Holocene record for Ecuador during the ∼≤4.7 ka BP. On the other hand, the lower portion of Mu logs represents the transition from normal to intermediate directions occurring at ∼≥5.6 ka BP. Sites from ET recorded two stable oblique reverse records with a large fluctuation far from the present GMF at ∼10.5 ka BP. The transitional virtual geomagnetic poles generally agree with those registered during the possible Pleistocene-Holocene excursion observed in other places of the planet. When plotted in a present world map, VGPs calculated from normal samples at QC are very well clustered in Northern North America, Greenland and Northern Europe; most VGP's calculated from Mu are situated between 30° and 60° northern latitude in Northern North America, Greenland, western Europe, Africa and North Pacific Ocean. Interestingly, the majority of the reverse directions from ET conforms a patch located in southern Africa, and a few ones are situated in central Africa, eastern Australia and Antarctica. An Ecuadorian paleopole was calculated with data resulting from QC and Mu. Also other paleopoles of the same age were processed from other North and South American sites. Remarkably they agree well, although they do not agree with the geographical pole showing ∼15o angular difference in relation to the rotation's axis of the Earth. Finally, is discussed the hypothesis of the global excursional state of the GMF during the last ∼11.0 ka BP and the potential use as dating tool the excursion dated at 10.5 ka BP.
Yutaka Yoshimura, Masakazu Fujii, Hideitsu Hino, Shotaro Akaho, Satoshi Kuriki, Osamu Ishizuka, Toshitsugu Yamazaki, Hyeon-Seon Ahn, Tesfaye Kidane, Yuhji Yamamoto, Yo-ichiro Otofuji Evidence for Missing Geomagnetic Reversals From Geomagnetic Reversal Frequency Model Using Adaptive Kernel Density Estimation Geophysical Research Letters, Volume 53, Issue 4, 28 February 2026, e2025GL120557 https://doi.org/10.1029/2025GL120557
Plain Language Summary
Earth's magnetic field has flipped many times in the past. Geologists use the timing of these flips, summarized in the geomagnetic polarity time scale (GPTS), to date rocks and sediments, but some flips may be missing from the standard timeline. We employed a statistical method of adaptive-bandwidth kernel density estimation to estimate the frequency of flips that occurred between approximately 155 million years ago and the present, and we inquired about the impact on this estimate when four newly recognized flips around 31 million years ago are incorporated into the GPTS timeline. Our analysis reveals fine-scale features of the geomagnetic reversal frequency over time and four intervals with unusually few flips after the end of a long, stable period in the Cretaceous. These low-activity intervals are separated by about 12–15.5 million years and align with unusually long periods of constant magnetic polarity. When the four new flips are included, the low-activity interval near 32 million years ago becomes less distinct. This pattern suggests that low-activity intervals may mark places where flips are still missing from the record.
Garima Shukla, B. V. Lakshmi, Jyotirmoy Mallik Magnetic Reversals During the Deccan Volcanism: Paleomagnetic Insights From the Pachmarhi Dykes Geochemistry, Geophysics, Geosystems Volume 27, Issue 3, March 2026, e2025GC012467 https://doi.org/10.1029/2025GC012467
Plain Language Summary
One of the largest volcanic provinces on Earth was formed by a series of massive volcanic eruptions that created the Deccan Traps ∼66 million years ago. Through cracks in the earth's crust, molten magma rises upward, solidifying into dykes cutting across the lava pile. We found ∼244 of these dykes in the Pachmarhi area, mostly east-west trending, in central India along the Narmada-Son lineament. These dykes once served as pathways that carried magma to the surface, helping feed the great lava outpourings that built the Deccan Traps. Similar features in the Nandurbar-Dhule regions show that these dykes were widespread, functioning as lava conduits during the Deccan volcanism. Some dykes preserve a normal magnetic field direction, while others show a reversed one, indicating that Earth's magnetic poles flipped during their formation. In this study, two of the studied dykes retained both normal and reversed magnetic signals, indicating that several magma pulses may have erupted, witnessing a geomagnetic reversal. Their estimated latitudes and recorded magnetic signals provide new evidence for the timing and dynamics of magma transport during Deccan volcanism.
N. Larsen, I. Usoskin, A. Mishev, S. Koldobskiy, P. Väisänen Reduced Geomagnetic Shielding During the Laschamps Excursion and Its Impact on Cosmic-Ray-Induced Atmospheric Radiation JGR Space Physics Volume 131, Issue 2, February 2026, e2025JA034820 https://doi.org/10.1029/2025JA034820
Abstract
The Laschamps geomagnetic excursion (≈41,000 years BP) was a period of significant weakening and incomplete reversal of the Earth's magnetic field. The weakening substantially reduced geomagnetic shielding against cosmic rays (CRs), which contribute to phenomena at Earth, such as cosmogenic isotope production, and atmospheric ionisation and radiation. In this work, we expand upon previous modeling of geomagnetic shielding during excursions and provide a robust methodology for assessing the CR impacts during such an event, focusing on CR-induced atmospheric radiation. This was achieved by updating the open-source OTSO CR trajectory tool to allow for paleomagnetic field models, namely LSMOD.2, to be used as inputs to compute global apparent geomagnetic cut-off rigidities at 100-year intervals throughout the excursion. The CRAC:DOMO model was used to assess the CR-induced atmospheric radiation, and the potential impact on the aviation industry was investigated by computing the effective dose rates for two representative flights, Helsinki to New York and Helsinki to Dubai, under various conditions. Results suggest low-latitude flights, normally well shielded under modern conditions, can experience significant increases in dose rates; in contrast, some high-latitude flight routes may observe decreases in radiation exposure due to the irregular geomagnetic structure during the excursion. These findings reveal that geomagnetic excursions can greatly enhance the levels of CR-induced atmospheric radiation, with wider implications that excursion events can likewise significantly affect other CR-induced processes, such as cosmogenic isotope production and atmospheric ionization. The methodology provided here outlines a framework under which CR impacts can be assessed under non-standard geomagnetic conditions.
Jeffrey J. Love, Greg M. Lucas, Anna Kelbert, E. Joshua Rigler, Paul A. Bedrosian, Neesha R. Schnepf. (2025) Mapping a Carrington Storm Geophysical Research Letters. 52, e2025GL116835. https://doi.org/10.1029/2025GL116835
Plain Language Summary
The 2 September 1859 Carrington storm was one of the most intense magnetic storms ever recorded by magnetometers. It disrupted telegraph communication around the world. Should a storm similar to the Carrington storm occur today, geoelectric fields induced in the Earth could disrupt electric-power transmission, damage power-grid systems, and cause blackouts that would carry significant economic costs. To inform projects for improving the resilience of electric-power-transmission systems, a map is presented of the strengths of geoelectric fields such as would be induced across the United States by a Carrington-class magnetic storm. Geoelectric fields are likely to be strongest in the East, in the vicinity of many large cities, and in the Midwest. Geoelectric-field strengths would exceed, in many places, benchmark values used in testing the resilience of power-transmission systems.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
V. M. Velasco Herrera, G. Velasco Herrera, W. Soon, A. Özgüç, N. Babynets, A. Tlatov, M. Švanda, S. Qiu, S. Baliunas, B. Kotan, G. González González, L. A. Bautista Flores, M. Pazos (2026) A New Method for Probabilistic Spatiotemporal Forecasts of Solar Soft X-Ray “S-Class” (>X10) Superflares Journal of Geophysical Research: Space Physics: Volume 131, Issue 2, e2025JA034977 https://doi.org/10.1029/2025JA034977
Plain Language Summary
Solar superflares, the most powerful explosions in our solar system, can cause severe disruptions to space technology and are very dangerous for the lives of astronauts, power grids, and communications systems on Earth. Forecasting these extreme events, including the most recent May 2024 storm event, has been one of the biggest challenges in the frontier of space weather science. In this study, we developed a new approach to forecast these superflares (classified as S-class or X10 class in soft X-rays) by analyzing nearly 50 years of satellite observations. We are proposing a paradigm shift; instead of trying to predict the exact location and time, we identify time windows and heliographic zones where the probability of superflares is significantly enhanced. Our analysis reveals that these extreme flares tend to occur in specific patterns that repeat over time. We found two key patterns: a 1.7-year cycle and a 7-year cycle that work together to create the identified high-risk periods including intense geomagnetic storms and Ground Level Enhancement events on Earth. Based on these patterns, we predict that the next high-risk window for superflares will occur around 2026–2027, with the southern hemisphere of the Sun being particularly more active.
Anthony Ficklin, Alessandro Bruno, Lauren Blum, Nicholas Cannady, T. G. Guzik, Ryuho Kataoka, Kazuoki Munakata, Yosui Akaike, Shoji Torii (2026) Effects of the May 2024 Solar Storm on the Earth's Radiation Belts Observed by CALET on the International Space Station Geophysical Research Letters. 53, e2025GL120032. https://doi.org/10.1029/2025GL120032
Plain Language Summary
The radiation environment of Earth typically consists of two separate structures: the inner radiation belt centered around L=1.5 (L is the distance in Earth radii between the center of the Earth’s equivalent magnetic dipole to a position at the magnetic equator), and the outer radiation belt at L≳4. Between the two is a slot region mostly devoid of relativistic (≳1 MeV) electrons. During exceptionally-strong geomagnetic storms it is possible for electrons from the outer radiation belt to be transported deep into this slot region and persist for an extended period. This occurred during the strongest geomagnetic storm in over 20 years on May 10-11, 2024. Count rates from the Calorimetric Electron Telescope (CALET) show that, following this event, relativistic electronsfrom the outer belt were pushed down to L-shell values of L≈2.2-3.2 and persisted there for over 5 months depending on energy. Estimated lifetimes of these electrons provide potential insight into the loss mechanisms for relativistic electrons in this region.
Bibek Rai, Bitap Raj Kalita, P. K. Bhuyan, Y. Otsuka, K. Shiokawa, D. Pallamraju (2026) Wind Induced F3 Layer in the Middle Latitude During the Mother's Day Geomagnetic Disturbances of 10–11 May 2024 Journal of Geophysical Research: Space Physics: Volume 131, Issue 2, e2025JA034833 https://doi.org/10.1029/2025JA034833
Plain Language Summary
On 10–11 May 2024, Earth experienced its most intense geomagnetic storm in over two decades. Such storms cause severe disturbances in the earth's upper atmosphere and the ionosphere, which in turn impact satellite/radio communication and navigation technologies. Using ionosonde data from India, Australia, Japan, and China, along with satellite and ground-based instrument data, this study reports the first clear evidence of the formation of an additional ionospheric layer (called F3 layer) at dawn in the middle latitudes. F3 layers were previously known to form mainly in the equatorial regions. We show that the mid-latitude F3 layer was formed due to strong storm-time equatorward winds and perturbed thermospheric composition changes. These results improve our understanding of extreme Space Weather impacts on Earth's upper atmosphere/ionosphere, which in turn impacts existing technologies and communication services.
Sheng Guo, Sicheng Wang, Lei Shi, Zheng Sheng, Jia Bu Analysis on Global Es Layer Response to the May 2024 Geomagnetic Storm Through a Combination of Tianmu-1 and COSMIC-2 Radio Occultation Observations Space Weather Volume 24, Issue 3, March 2026, e2025SW004792 https://doi.org/10.1029/2025SW004792
Plain Language Summary
The Chinese Tianmu-1 commercial satellite constellation has provided a large number of ionospheric RO profiles, for the first time, enabling a global analysis of the Es layer behavior during a G5-level geomagnetic storm in May 2024. Analysis reveals that the global Es layer was significantly disturbed during the storm, with distinct latitudinal and longitudinal behaviors. Based on observational evidence, potential mechanisms for the formation of the storm-time Es layer are indicated in this study. First, particle precipitation likely caused the enhancement of Es intensity (EsI) at high latitudes, while the intense eastward prompt penetration electric field may be the primary driver for mid-to-low-latitudes EsI depletion during the main phase. Second, storm-driven neutral winds may have contributed to Es layer development over the Australia-Asia and Southeast Pacific sectors in the Southern Hemisphere. Third, F-region ionosphere perturbations may exert downward influences on the underlying Es region.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Xinling Zou, Lin Su, Zhisheng Zhang, Xiaomin Lin, Mang Lin Surface Air Enrichment of Cosmogenic 35S at a Subtropical Site During the May 2024 Solar Superstorm Geophysical Research Letters, Volume 53, Issue 5, March 2026, e2025GL120852 https://doi.org/10.1029/2025GL120852
Plain Language Summary
Sulfur-35 (35S) is a radioactive isotope that forms high in the atmosphere when energetic particles from space hit air molecules. Because its production is strongest in the stratosphere, increases in 35S near the ground usually indicate that stratospheric air has mixed downward. In May 2024, Earth experienced the most powerful solar storm since 2003. We measured 35S in daily aerosol samples from Guangzhou, China, and observed two unusual spikes. One spike on May 16 was clearly caused by a deep intrusion of stratospheric air, which also brought large amounts of ozone to the surface and led to a regional air pollution episode. However, another period of high 35S on May 9–15 could not be explained by stratospheric transport. Instead, it coincided with strong bursts of solar energetic particles entering the atmosphere during the solar storm. Our results suggest that extreme solar events may temporarily increase atmospheric 35S production. Further research on how cosmogenic radionuclides respond to extreme solar activity could deepen our understanding of past solar storms and improve predictions of their future intensity and frequency, thereby enabling better assessment of impacts on spacecraft and radio communications and potential effects on humans and ecosystems.
B. Wehmeyer1,2,3,4*, A. Yagüe López5, B. Côté2,3,6, M.K. Pető2,3, C. Kobayashi4 and M. Lugaro2,3,7,8 (2024) Galactic chemical evolution with the short-lived isotopes 53Mn, 60Fe, 182Hf, and 244Pu EPJ Web of Conferences Volume 297, 01016 https://doi.org/10.1051/epjconf/202429701016
Abstract
We run a three-dimensional Galactic chemical evolution (GCE) model to follow the propagation of 53Mn from supernovae of type Ia (SNIa), 60Fe from core-collapse supernovae (CCSNe), 182Hf from intermediate mass stars (IMSs), and 244Pu from neutron star mergers (NSMs) in the Galaxy. We compare the GCE of these short-lived radioactive isotopes (SLRs) to recent detections on the deep-sea floor. We find that although these SLRs originate from different sites, they often arrive conjointly on Earth.
Rebecca A. Booth, Anna Ordog, Jo-Anne Brown, T. L. Landecker, Alex S. Hill, Jennifer L. West, Minjie Lei, S. E. Clark, Andrea Bracco, John M. Dickey, and Ettore Carretti A Three-dimensional Model for the Reversal in the Local Large-scale Interstellar Magnetic Field The Astrophysical Journal, Volume 997, Number 2, January 2026. https://doi.org/10.3847/1538-4357/ae28d1
Abstract
We probe the three-dimensional geometry of the large-scale Galactic magnetic field within 1 kpc of the Sun using the Dominion Radio Astrophysical Observatory Global Magneto-Ionic Medium Survey (GMIMS) of the Northern Sky (DRAGONS). DRAGONS is a new full polarization survey of the northern sky from 350 to 1030 MHz covering decl. of –20° < δ < 90° and a component of GMIMS. The first moment of the Faraday depth (FD) spectra produced from DRAGONS above 500 MHz reveals large-angular-scale FD structures with signs that alternate only once in the southern Galactic hemisphere and twice in the northern hemisphere, patterns shared by other Faraday rotation datasets. DRAGONS is the first survey to achieve high FD resolution while maintaining sensitivity to broad FD structures, enabling the first use of Galactic longitude–FD plots. These plots reveal Faraday-complex structures across the sky, indicating a slablike scenario in which emission and Faraday rotation are mixed. This complexity is overlaid on the same large-scale FD patterns that appear in the first moment map. We model these patterns as a magnetic reversal slicing through the disk on a diagonal and passing above the Sun in Galactic coordinates. We describe this reversal as a plane with a normal vector parallel to the line directed along (ℓ, b) = (168° 5', −60°) and estimate its distance to be between 0.25 and 0.55 kpc. Our results show that much of the observed Faraday sky may be dominated by the local magnetic field configuration.
Grant, S. R., & Jones, G. H. (2025). Prospects for the Crossing of Comet 3I/ATLAS’s Ion Tail. Research Notes of the AAS, 9(10), 276. https://doi.org/10.3847/2515-5172/ae12e6
Abstract
During October - November 2025, interstellar comet 3I/ATLAS, will pass upstream of the Europa Clipper and Hera spacecraft. Here, we identify two potential opportunities for in-situ observations of 3I’s ion tail by immersion, facilitated by the close alignment between the comet’s hyperbolic trajectory with the ecliptic plane. Duringthe period 30 October - 6 November 2025, it is predicted that Europa Clipper will potentially be immersed within the ion tail of 3I/ATLAS, providing the opportunity todetect the signatures of an interstellar comet’s ion tail. Characteristic changes to the solar wind are also expected to be observed; a magnetic draping structure associated with the comet may be identifiable. It is further predicted that spacecraft Hera will possibly be immersed within the ion tail of 3I/ATLAS during the period 25 October- 1 November 2025.
T. Cavalié, R. Moreno, C. Lefour, B. Benmahi, T. Fouchet, E. Lellouch, É. Ducreux, M. Gurwell, F. Gueth, L. N. Fletcher, D. Bardet Observations of the temporal evolution of Saturn's stratosphere following the Great Storm of 2010-2011. II. Latitudinal distribution of CO and stratospheric winds. Astronomy & Astrophysics, arXiv preprint arXiv:2601.20359, 2026 https://doi.org/10.48550/arXiv.2601.20359
Abstract
Saturn's Great Storm of 2010-2011 has produced two stratospheric hot spots, the "beacons," that eventually merged to produce a gigantic one in April and May 2011. This beacon perturbed stratospheric temperatures, hydrocarbon, and water abundances for several years. We aim to assess whether the beacon induced any perturbation in another oxygen species, namely CO. A second goal is to measure how the vortex perturbed the stratospheric wind regime. We conducted interferometric observations of Saturn in the submillimeter range with SMA and ALMA to spatially resolve the CO (J=3-2) and (J=2-1) emissions, respectively. We used a previously determined CO vertical profile as a template, to search for (i) the meridional distribution of CO and (ii) variations of the CO abundance associated with the storm. The high spatial and spectral resolutions of the ALMA observations enabled us to retrieve the winds from the Doppler shifts induced by the winds on the lines. Despite limitations resulting from the removal of baseline ripples, we find a relatively constant meridional distribution of CO. The average CO mole fraction implied by the adopted and rescaled 220-year-old-comet-impact vertical profile is (1.70.7) at 0.3\,mbar, i.e., where the contribution functions peak. We also find that the CO abundance has not been noticeably altered in the beacon. The winds measured at 1\,mbar show striking differences with those measured in 2018, after the demise of the beacon. We find the signature of the vortex as an anticyclonic feature. The equatorial prograde jet is 100 to 200 m.s slower, and broader in latitude, than in quiescent conditions. We also detect several prograde jets in the southern hemisphere. Finally, we detect a retrograde jet at 74N which could be a polar jet caused by the interaction of the Saturn magnetosphere with its atmosphere.
Jamie M. Jasinski, Henrik Melin, James A. Sinclair, Sophia Zomerdijk-Russell, Nick Achilleos, Carol Paty Uranus' Long-Term Thermospheric Cooling Is Unlikely to Be Primarily Driven by the Solar Wind Geophysical Research Letters, Volume 52, Issue 24. December 2025, e2025GL119362 https://doi.org/10.1029/2025GL119362
Abstract
Since the 1980's until present day, the temperature of the upper atmosphere at Uranus has been steadily declining (i.e., cooling). The reason for this is currently unexplained. Multiple ideas have been put forth to explain this. This includes the solar wind as a driver of the temperature, since its power is also lower now compared to the 1980's. We show that since the start of solar cycle 24 in 2009 the solar wind power at Uranus has generally increased while the upper atmospheric temperature has continued to monotonically decline in the same timeframe, showing that they are not correlated. If the solar wind power did drive the temperature, then we would have expected a gradual increase in the temperature over the last ∼16 yrs. We have also calculated that there is not enough energy lost from a decline in solar wind power to cool the upper atmosphere.
D. Bhattacharyya, J. T. Clarke, P. Stephenson, T. Koskinen, J.-Y. Chaufray, L. Moore, H. Melin Steady Collapse of Uranus' Exosphere After 1998 to the Present Decade Geophysical Research Letters, Volume 53, Issue 6. March 2026, e2025GL120292 https://doi.org/10.1029/2025GL120292
Plain Language Summary
Uranus' thermosphere has been steadily cooling since the Voyager 2 flyby in 1986 to the present decade. Spitzer spacecraft's infrared observations indicate that this cooling is not matched by the lower atmosphere (pressure >1 μbar). We have used Hubble Space Telescope observations of the upper atmosphere of Uranus in the far ultraviolet from 1998 to 2022 to show that the region above the thermosphere, that is, the exosphere, has also been experiencing long-term cooling like the thermosphere, but only after 1998, irrespective of auroral activity. The processes responsible for this upper atmospheric cooling are unknown at present. Determining the vertical density structure of the thermosphere and exosphere and its correlation with Uranus' seasons and solar wind intensity provides key insight into upper-atmospheric variability. For example, the seasonal changes in upper atmospheric density drive the amount of frictional drag experienced by ring particles, which in turn determines the lifetime and temporal survivability of the ring system. Variations in density also regulate the amount and energy of charged particles entering the upper atmosphere along open magnetic field lines. These particles heat the upper atmosphere and contribute significantly to the planet's total energy budget.
Geology & Earthquakes
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Tomohiro Ohuchi 1,*, Takaaki Kawazoe 1,2, Yuji Higo 3, Ken-ichi Funakoshi 3,4, Akio Suzuki 5, Takumi Kikegawa 6, Tetsuo Irifune 1,7 Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth’s upper mantle Sci Adv. 2015 Oct 2;1(9):e1500360. https://doi.org/10.1126/sciadv.1500360
Abstract
Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth’s upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 1019.6 to 1020.7 Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size–sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle.
Erdinç Timoçin, İlkin Özsöz, Oya Ankaya Pamukçu Possible seismomagnetic disturbances prior to the 23 April 2024 Marmara earthquake: evidence from ground-based magnetometer observations Advances in Space Research, 2026, ISSN 0273-1177 https://doi.org/10.1016/j.asr.2026.01.094
Abstract
Electromagnetic anomalies in the Earth’s magnetic field have long been investigated as potential short- and medium-term precursors to earthquakes, reflecting processes such as stress accumulation, microfracturing, and charge migration within the crust. Documenting these signals is essential for understanding lithosphere–atmosphere–ionosphere coupling mechanisms and for assessing their potential role in earthquake forecasting. This study examines possible geomagnetic anomalies before, during, and after the Mw 6.2 earthquake that struck the Marmara Sea in northwestern Türkiye on April 23, 2025. One-minute geomagnetic field data from three ground-based observatories—IZN (proximal to the epicentre) and PEG and PAG (more distant reference stations)—were analyzed. The rate of change of the geomagnetic field (ROG) and the corresponding ROG Index (rogi), reflecting the relative intensity of these variations, were calculated. To suppress external influences from space weather, data were filtered using X-ray flux, Dst, and Kp indices. Two short-duration, high-amplitude magnetic disturbances were detected exclusively at the IZN station—approximately five days and five minutes before the mainshock—while no such anomalies were observed at the control stations. On April 23, the geomagnetic environment remained quiet, with X-ray flux limited to the C-class, Kp values below 3, and Dst not dropping below –50 nT. These conditions support a local, seismogenic origin for the anomalies. Notably, the sharp pre-seismic increase in rogi suggests a seismomagnetic response, potentially driven by piezoelectric, electrokinetic, or thermoionic mechanisms. These findings provide novel evidence that electromagnetic precursors can be detected even for moderate-magnitude earthquakes and represent the first high-resolution ground-based observations of geomagnetic field disturbances associated with the April 23 Marmara Sea event.
