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Earth’s magnetic field is presently characterized by a large and growing anomaly in the South Atlantic Ocean. The question of whether this region of Earth’s surface is preferentially subject to enhanced geomagnetic variability on geological timescales has major implications for core dynamics, core−mantle interaction, and the possibility of an imminent magnetic polarity reversal. Here we present paleomagnetic data from Saint Helena, a volcanic island ideally suited for testing the hypothesis that geomagnetic field behavior is anomalous in the South Atlantic on timescales of millions of years. Our results, supported by positive baked contact and reversal tests, produce a mean direction approximating that expected from a geocentric axial dipole for the interval 8 to 11 million years ago, but with very large associated directional dispersion. These findings indicate that, on geological timescales, geomagnetic secular variation is persistently enhanced in the vicinity of Saint Helena. This, in turn, supports the South Atlantic as a locus of unusual geomagnetic behavior arising from core−mantle interaction, while also appearing to reduce the likelihood that the present-day regional anomaly is a precursor to a global polarity reversal.

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. Graphical Abstract

We describe a new, original approach to the modelling of the Earth’s magnetic field. The overall objective of this study is to reliably render fast variations of the core field and its secular variation. This method combines a sequential modelling approach, a Kalman filter, and a correlation-based modelling step. Sources that most significantly contribute to the field measured at the surface of the Earth are modelled. Their separation is based on strong prior information on their spatial and temporal behaviours. We obtain a time series of model distributions which display behaviours similar to those of recent models based on more classic approaches, particularly at large temporal and spatial scales. Interesting new features and periodicities are visible in our models at smaller time and spatial scales. An important aspect of our method is to yield reliable error bars for all model parameters. These errors, however, are only as reliable as the description of the different sources and the prior information used are realistic. Finally, we used a slightly different version of our method to produce candidate models for the thirteenth edition of the International Geomagnetic Reference Field.

We present the extension of the Kalmag model, proposed as a candidate for IGRF-13, to the twentieth century. The dataset serving its derivation has been complemented by new measurements coming from satellites, ground-based observatories and land, marine and airborne surveys. As its predecessor, this version is derived from a combination of a Kalman filter and a smoothing algorithm, providing mean models and associated uncertainties. These quantities permit a precise estimation of locations where mean solutions can be considered as reliable or not. The temporal resolution of the core field and the secular variation was set to 0.1 year over the 122 years the model is spanning. Nevertheless, it can be shown through ensembles a posteriori sampled, that this resolution can be effectively achieved only by a limited amount of spatial scales and during certain time periods. Unsurprisingly, highest accuracy in both space and time of the core field and the secular variation is achieved during the CHAMP and Swarm era. In this version of Kalmag, a particular effort was made for resolving the small-scale lithospheric field. Under specific statistical assumptions, the latter was modeled up to spherical harmonic degree and order 1000, and signal from both satellite and survey measurements contributed to its development. External and induced fields were jointly estimated with the rest of the model. We show that their large scales could be accurately extracted from direct measurements whenever the latter exhibit a sufficiently high temporal coverage. Temporally resolving these fields down to 3 hours during the CHAMP and Swarm missions, gave us access to the link between induced and magnetospheric fields. In particular, the period dependence of the driving signal on the induced one could be directly observed. The model is available through various physical and statistical quantities on a dedicated website at https://ionocovar.agnld.uni-potsdam.de/Kalmag/.

Observations of the geomagnetic field taken at Earth’s surface and at satellite altitude are combined to construct continuous models of the geomagnetic field and its secular variation from 1957 to 2020. From these parent models, we derive candidate main field models for the epochs 2015 and 2020 to the 13th generation of the International Geomagnetic Reference Field (IGRF). The secular variation candidate model for the period 2020–2025 is derived from a forecast of the secular variation in 2022.5, which results from a multi-variate singular spectrum analysis of the secular variation from 1957 to 2020.

The South Atlantic Anomaly (SAA) is a region at Earth’s surface where the intensity of the magnetic field is particularly low. Accurate characterization of the SAA is important for both fundamental understanding of core dynamics and the geodynamo as well as societal issues such as the erosion of instruments at surface observatories and onboard spacecrafts. Here, we propose new measures to better characterize the SAA area and center, accounting for surface intensity changes outside the SAA region and shape anisotropy. Applying our characterization to a geomagnetic field model covering the historical era, we find that the SAA area and center are more time dependent, including episodes of steady area, eastward drift and rapid southward drift. We interpret these special events in terms of the secular variation of relevant large-scale geomagnetic flux patches on the core–mantle boundary. Our characterization may be used as a constraint on Earth-like numerical dynamo models.

We present a candidate mean secular variation (SV) model for the 2025.0 - 2030.0 period. The forecasted SV is produced with a data assimilation (DA) system built around a simple frozen-flux model of the core flow and magnetic field near the core–mantle boundary (CMB). An Ensemble Kalman Filter (EnKF) and smoother (EnKS) are used to assimilate Gauss coefficients from the Kalmag field model, to estimate a core flow which is then used to predict changes in the magnetic field. This forecast methodology is tested against past 5-year periods where it is found to be effective in predicting mean SV, and is superior to an otherwise identical setup using an EnKF alone (no EnKS). The inferred core flow is examined and is seen to exhibit structures consistent with the eccentric gyre and westward drift found in traditional inversions. While this study presents an SV candidate, its secondary purpose is to explore and highlight the potential of the EnKS methodology in understanding the geodynamo. Notably, the EnKS algorithm we use requires no adjoint for the model and can be implemented into already existing EnKF-based systems. The ease of implementation and improvement provided by the EnKS make it a desirable addition to other geomagnetic data assimilation systems, particularly those built around full, 3-D numerical dynamo models, for which the production and maintenance of an adjoint can be challenging. Graphical Abstract

Our new paleomagnetic data provide the timescale for the eruptive sequence of the 45 ka Shikotsu caldera-forming eruption of VEI 7. The duration of the entire sequence is estimated to be centuries, which is considerably longer than previously thought. The studied volcanic sequence, located at ~ 10 km from the caldera rim, includes five units of pyroclastic flow deposits (units B3, C1, C2, D, and E in ascending order) and an uppermost pyroclastic surge deposit (unit F2). The ash matrix samples of the pyroclastic deposits, predominantly composed of juvenile material, were collected into aluminum and plastic cubes, which were precisely oriented using an originally designed tool set. As a result, the obtained paleomagnetic directions have high precision parameters (k = 200–1400) and small 95% confidence intervals (α 95  = 2–4°). These paleomagnetic directions determined from the sequence of the six units demonstrate a curve of paleomagnetic secular variation, which has a total angular distance of 14.4 ± 4.1°. The observed distinguishable paleomagnetic directions indicate that the earlier four units (B3, C1, C2, and D) were formed by four distinct eruptions over a period of 240 ± 70 years with repose times of decades between the eruptions. The indistinguishable paleomagnetic directions indicate that the three late-stage units (D, E, and F) were erupted in a short period, decades or less. Our new paleomagnetic data, combined with the reported petrological change in pumice, suggest that the extractions of crystal-poor rhyolitic melt from the magma chamber occurred in multiple eruptions over a considerable period (more than a hundred years). Graphical Abstract

The International Geomagnetic Reference Field (IGRF) is a spherical harmonic model representing the large-scale Earth’s main magnetic field and its secular variation (SV). In 2024, the International Association of Geomagnetism and Aeronomy (IAGA) V-MOD Working Group called for candidate models for the 14th generation of IGRF (IGRF-14). Inspired by successful launch of the Macau Science Satellite-1 (MSS-1) on May 21, 2023, Macau Institute of Space Technology and Application (MISTA) and the MSS-1 team submitted three candidate models based on newly acquired magnetic data: a main field model for epoch 2020.0, a main field model for epoch 2025.0, and an average SV model for the period 2025.0–2030.0. The 2020.0 model was contributed by Swarm satellite and ground observatory data, while the 2025.0 and SV models incorporated the latest magnetic data from MSS-1, Swarm and global observatories. This paper describes the construction and evaluation of these candidate models. The results of the evaluation show strong consistency between the MISTA candidate models and the officially released IGRF-14 models, confirming the reliability of our candidate models and the high quality of MSS-1 magnetic data. We also assess the unique contribution of MSS-1 data. Our discussion emphasizes the complementary value of combining observations from polar-orbiting satellites like Swarm with those from low-inclination missions like MSS-1 to improve the resolution of Earth’s magnetic field model. Graphical Abstract

Although paleomagnetic secular variations (PSV) often corroborate radiocarbon (14C)-based lacustrine sediment chronologies, this is not the case at the high-altitude site Khar Nuur in the Mongolian Altai Mountains. Our results show that the inclination pattern resembles those from a regional reference record from Shireet Naiman Nuur and global geomagnetic field models very well, but with a constant offset of 730 ± 90 yr. Possible reservoir effects from terrestrial pre-aging and hardwater effects can be excluded as the cause of the ∼730-yr offset because the different dated compounds correspond very well to each other, and modern reservoir effects are negligible. Instead, the constant ∼730-yr offset in the PSV pattern is likely the result of a constant lock-in depth of 26 ± 2 cm below the sediment-water interface at Khar Nuur. This assumption is supported by comparison of paleoclimatological proxies from Shireet Naiman Nuur, where similarities are obvious for the 14C-based chronology of Khar Nuur without a ∼730-yr adjustment. Therefore, the previously published 14C-based chronology of Khar Nuur provides a reliable age control. Accepting the lock-in depth of 26 ± 2 cm, the good consistency in inclination between Khar Nuur and global geomagnetic field models highlights the reliability of the latter even in a paleomagnetically understudied area.