Explore the vast range of titles available.

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.

Continuous satellite measurements of the Earth's magnetic field have advanced the characterization of spatial‐temporal variations of the main field over the past two decades. To comprehend the underlying mechanism responsible for the geomagnetic field variations, we develop a novel core surface flow inversion scheme based on physics‐informed neural networks. The inversion method can account for the secular variation contributed by the interaction between the core flow and undetectable small‐scale magnetic fields. Based on the novel inversion framework, we derive a time‐dependent core surface flow model between 2000 and 2022 from the CHAOS‐7 core field model. The inverted core flow is then analyzed using the dynamic mode decomposition to extract wave‐like fluid motions. By calculating the magnetic secular acceleration contributed by each dynamic mode, we identify that the dynamic modes with period of about 10 and 7 years are responsible for geomagnetic jerks in the Atlantic and Pacific equatorial regions. Plain Language Summary Over the past two decades, satellites have been continuously monitoring the Earth's magnetic field. The major part of the field comes from the liquid part of the Earth's core. Geomagnetic measurements show quick changes in the field, including sudden shifts known as geomagnetic jerks. These shifts are believed to be linked to specific fluid motions in the Earth's core. Our study aims to better understand these flows and their effects. We use a method involving neural networks to figure out the patterns of flow at the core surface from the satellite data. We then use a technique to separate these flow patterns into simpler wave‐like forms. This helps us see how each wave pattern affects changes in the magnetic field. Our findings suggest that wave‐like motions with period of about 10 and 7 years caused geomagnetic jerks in the Atlantic and Pacific regions near the equator. Key Points A novel core surface flow inversion scheme based on physics‐informed neural networks is developed The inverted flow from the CHAOS‐7 model is analyzed using the dynamic mode decomposition to extract wave‐like flow patterns Geomagnetic jerks in the Atlantic and Pacific equator are related to two dynamic modes with period about 10 and 7 years

Paleomagnetic studies typically assume that the long‐term, time‐averaged geomagnetic field behaves as a geocentric axial dipole (GAD). While paleodirectional data over the past five million years generally agree with GAD predictions, mid‐to‐low latitude paleointensity records fail to show GAD, with high values from Hawaii. Possible causes include experimental biases, non‐dipole field contributions, and uneven temporal sampling. In this study, we conduct alternating field and thermal demagnetization measurements, as well as paleointensity experiments, on 12 late Pleistocene (∼0.2–0.5 Ma) lava flows from northern Hainan Island (∼20°N, ∼110°E) of the Brunhes normal polarity chron. Eleven sites yield stable paleomagnetic directions (D = 9.1°, I = 24.3°, α95 = 4.0°), defining a virtual geomagnetic pole (VGP) at 78.7°N, 237.7°E, with VGP dispersion of 12.9°. Paleointensity results from four qualified sites range from 28.8 to 48.9 μT (mean = 37.8 ± 6.9 μT), which are in agreement with the Brunhes Hawaiian data from the same latitude. The directional and intensity results from Hainan are consistent with previous studies at similar latitudes but deviate from GAD predictions. Our results suggest that the high paleointensity values observed in the Hawaiian region may result from differences in age distributions compared with records from other latitudes. Considering these temporal differences, the observed non‐GAD characteristics at mid‐to‐low latitudes may partly reflect comparisons between time‐averaged field properties over distinct geological intervals.

Measurements from low Earth orbit satellites play an important role in modern geomagnetic field modelling. In this study, we present two geomagnetic field models, WHUEMM-S, derived by sequential inversion, and WHUEMM-C, derived by comprehensive inversion. Both models are constructed from calibrated Swarm A/B, GRACE-FO 1, and CryoSat-2 observations collected between January 2019 and July 2024. Both models represent the core field with degree 15 spherical harmonics and temporal sixth order B-splines. This study assesses the impact of these inversion strategies and evaluates the value of non-dedicated satellites in geomagnetic field modelling. Power spectral analysis shows that both models produce a temporally stable main field (MF) energy and secular variation (SV) energy, with differences from CHAOS-7.18 of about 1 nT 2 and 1 (nT/year) 2 for spherical harmonic degrees below 6. Stronger regularization damping in WHUEMM causes a sharp decrease in secular acceleration (SA) at degrees above 7. WHUEMM-C departs from CHAOS-7.18 mainly in the axial dipole and a few low-order sectoral terms, whereas the high-degree misfits in WHUEMM-S are probably driven by spectral truncation and residual external signals. Global MF maps confirm that both models reproduce mid- and low-latitude features well; however, at high latitudes WHUEMM-S deviates more from CHAOS-7.18 than WHUEMM-C does. SV derived from observatory records confirm that each model maintains smooth temporal end points and reliably captures long-term trends. This demonstrates that carefully calibrated, non-dedicated data from GRACE-FO 1 and CryoSat-2 can be used to build global geomagnetic models without compromising robustness. Finally, using WHUEMM-S as the parent model, we produced and submitted three IGRF-14 candidate models. Graphical Abstract

A record of the geomagnetic field on the ground sometimes shows smooth daily variations on the order of a few tens of nano teslas. These daily variations, commonly known as Sq, are caused by electric currents of several μ A / m 2 flowing on the sunlit side of the E-region ionosphere at about 90–150 km heights. We review advances in our understanding of the geomagnetic daily variation and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the non-specialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the geomagnetic daily variation are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.

This study presents results of mapping three-dimensional (3-D) variations of the electrical conductivity in depths ranging from 400 to 1200 km using 6 years of magnetic data from the Swarm and CryoSat-2 satellites as well as from ground observatories. The approach involves the 3-D inversion of matrix Q-responses (transfer functions) that relate spherical harmonic coefficients of external (inducing) and internal (induced) origin of the magnetic potential. Transfer functions were estimated from geomagnetic field variations at periods ranging from 2 to 40 days. We study the effect of different combinations of input data sets on the transfer functions. We also present a new global 1-D conductivity profile based on a joint analysis of satellite tidal signals and global magnetospheric Q-responses.

The Earth’s magnetic field displays variations on a broad range of time scales, from years to hundreds of millions of years. The last two decades of global and continuous satellite geomagnetic field monitoring have considerably enriched the knowledge on the rapid physical processes taking place in the Earth’s outer core. Identification of axisymmetric torsional Alfvén waves with subdecadal periods from observatory and satellite data has given access to an averaged intensity of the magnetic field in the Earth’s core interior. A significant part of the rapid signal, however, resides in nonaxisymmetric motions. Their origin has remained elusive, as previous studies of magnetohydrodynamic waves in the Earth’s core mainly focused on their possible signature on centennial time scales. Here, we identify nonaxisymmetric wavelike patterns in the equatorial region of the core surface from the observed geomagnetic variations. These wavelike features have large spatial scales, interannual periods in the vicinity of 7 y, amplitudes reaching 3 km/y, and coherent westward drift at phase speeds of about 1,500 km/y.We interpret and model these flows as the signature of Magneto–Coriolis (MC) eigenmodes. Their identification offers a way to probe the cylindrical radial component of the magnetic field inside Earth’s core. It follows from our work that there is no need for a stratified layer at the top of the core to account for the rapid geomagnetic field changes.

Knowing when the geodynamo started is important for understanding the evolution of the core, the atmosphere, and life on Earth. We report full-vector paleointensity measurements of Archean to Hadean zircons bearing magnetic inclusions from the Jack Hills conglomerate (Western Australia) to reconstruct the early geodynamo history. Data from zircons between 3.3 billion and 4.2 billion years old record magnetic fields varying between 1.0 and 0.12 times recent equatorial field strengths. A Hadean geomagnetic field requires a core-mantle heat flow exceeding the adiabatic value and is suggestive of plate tectonics and/or advective magmatic heat transport. The existence of a terrestrial magnetic field before the Late Heavy Bombardment is supported by terrestrial nitrogen isotopic evidence and implies that early atmospheric evolution on both Earth and Mars was regulated by dynamo behavior.

Fluctuations in the geomagnetic field occur over a broad range of timescales. Short‐period fluctuations are called secular variation, whereas excursions and reversals are viewed as anomalous transient events. An open question is whether distinct mechanisms are required to account for these different forms of variability. Clues are sought in trends b of the axial dipole moment from six time‐dependent geomagnetic field models. Variability in b has a well‐defined dependence on the time interval (or window) for the trend. The variance of b reveals a simple relationship to trends during excursions and reversals. This connection hints at a link between reversals, excursions and secular variation. Stochastic models exhibit a similar behavior in response to random fluctuations in dipole generation. We find that excursions, reversals and secular variation can be distinguished on the basis of trend durations rather than differences in the underlying physical process. While this analysis does not rule out distinct physical mechanisms, the paleomagnetic observations suggest that such distinctions are not required. Plain Language Summary Geomagnetic field models capture details of excursions and reversals over the past 2 Myr. A comparison of these transient events with field behavior during times of stable polarity offers insights into the underlying physical mechanisms. The focus of comparison is the trend of the axial dipole moment over a prescribed duration. Six geomagnetic field models reveal consistent and predictable changes in the variance of dipole trends as a function of duration. Trends into reversals and excursions can also be recovered from the geomagnetic field models. A simple relationship between transient events and the trends during stable polarity hints at a common underlying mechanism. This connection is supported by a stochastic model for dipole fluctuations, which is capable of reproducing the observed changes in the trend variance with duration. The same model quantitatively reproduces the relationship between transient events and secular variation. Given that trends in the stochastic model are driven entirely by fluctuations in dipole generation, a similar interpretation may account for excursions, reversals and secular variation without requiring different physical mechanisms. Key Points Statistics of dipole trends are computed for six paleomagnetic field models Trends during excursions and reversals are linked to variability during stable polarity A relationship between excursions, reversals and secular variation suggests a common underlying mechanism

We present a mid‐to‐late Holocene record of relative paleosecular variation from the Ross Sea region of Antarctica. The 6,700‐year‐long record of inclination, declination, and relative paleointensity from a marine sediment core collected near Cape Adare is independently dated using a combination of ramped pyrolysis oxidation and carbonate radiocarbon dates. Agreement between the large‐scale features of the relative paleointensity record and the virtual axial geomagnetic dipole moment suggests that changes in the record are dominated by the dipole component of the Earth's geomagnetic field. Correspondence between the record and a non‐independently dated reconstruction from the Antarctic Peninsula indicates regionally coherent changes in the geomagnetic field intensity in the southern high latitudes during the mid‐to‐late Holocene. The prominent features of the record serve as stratigraphic markers for hard‐to‐date Antarctic sedimentary records and a constraint on Holocene geomagnetic field behavior when incorporated into the next generation of geomagnetic field models. Key Points A relative paleosecular variation record for mid‐to‐late Holocene (past 6.7 ka) is derived from marine sediments from the Ross Sea, Antarctica The record is independently dated using novel radiocarbon dating methodologies and resembles the global virtual axial dipole moment The prominent features of the record can serve as correlation and dating tools and a constraint on Holocene geomagnetic field behavior