Article
Geochemistry & Geophysics
Julien Aubert, Nicolas Gillet
Summary: The study uses a geodynamo simulation model to analyze the interactions between slow convective motions and fast hydromagnetic waves in Earth's core, identifying three classes of fluid dynamic and hydromagnetic waves. These waves enrich and flatten the energy density spectrum of geomagnetic acceleration at decadal timescales, providing constraints on the observed frequency power spectrum.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Julien Aubert, Philip W. Livermore, Christopher C. Finlay, Alexandre Fournier, Nicolas Gillet
Summary: By analyzing numerical geodynamo simulation and comparing with actual observations, it is found that geomagnetic jerks originate from the interaction between slow convection and rapid hydromagnetic wave propagation in the Earth's outer core. The simulation results support the hypothesis that the emission of magneto-inertial waves following a disruption of the leading-order force balance is the single physical root cause for jerks observed throughout the geomagnetic record.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Julien Aubert
Summary: Our understanding of the geodynamo has advanced recently thanks to improved geomagnetic data and realistic numerical simulations. Using a sequential, ensemble-based framework, high-resolution geomagnetic field models are assimilated into a numerical geodynamo simulation, resulting in an estimate of the present state and dynamics of Earth's core. The simulations accurately reproduce known features of the geodynamo, and the convective power is estimated at 2.95 +/- 0.2 TW. These physically realistic models allow for the study of deep Earth properties through geomagnetic data assimilation.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
P. A. Davidson, A. Ranjan
Summary: Numerical simulations of the geodynamo show that the dynamo action is primarily driven by the effects of helicity, while differential rotation plays a secondary role. The simulations reveal several robust features, such as thin convective columns outside the tangent cylinder with a left-handed helicity in the north and right-handed helicity in the south, 2-D motion in the equatorial regions, positive radial current at mid-latitudes and negative radial current in the equatorial regions, radial outflow in the equatorial regions, and elevated temperatures near the equator. The high equatorial temperatures are a direct consequence of the skew-symmetric distribution of helicity, resulting in an anisotropic turbulent diffusion that preferentially carries heat radially outward along the equator.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
T. Schwaiger, T. Gastine, J. Aubert
Summary: This passage discusses the importance of measuring length scales with both energetic and dynamic relevance in fluid dynamics. It analyzes two length scales in magnetic and non-magnetic models that achieve this dual relevance, revealing different interpretations and misrepresentations of force balance. By focusing on these scales, the study uncovers insights into the underlying mechanisms of dynamo systems and their dominant length scales.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
M. Istas, N. Gillet, C. C. Finlay, M. D. Hammer, L. Huder
Summary: In this study, the pygeodyn data assimilation tool is used to analyze ground and satellite-based geomagnetic data sets. The dynamics of the Earth's outer core on interannual to decadal timescales is investigated, and new findings on the operation of quasi-geostrophic Magneto-Coriolis waves are reported. An improved ensemble Kalman filter algorithm is introduced, which takes into account cross-correlations between variables, resulting in better stability and reduced computational cost. The updated scheme also allows for the use of observations in different forms, enabling global constraints on core dynamics even at short periods.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
K. Gwirtz, M. Morzfeld, W. Kuang, A. Tangborn
Summary: Geomagnetic data assimilation combines past and present observations of Earth's magnetic field with numerical models to initialize forecasts. A new 'proxy model' is introduced to test numerical techniques for geomagnetic data assimilation at lower computational cost. Using proxy models as 'gate-keepers' for numerical methods has proven useful in numerical weather prediction, helping to improve forecast skill.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
Michael A. Calkins, Ryan J. Orvedahl, Nicholas A. Featherstone
Summary: The dynamics of convection-driven dynamos in a spherical shell, relevant to the geodynamo, were analyzed using numerical simulation data and asymptotic theory. The results showed that the Lorentz force is weaker than the mean buoyancy force across different Ekman numbers and thermal forcings, with a relative difference in forces of O(Ek(1/6)) within the investigated parameter space. The study also found that the mean zonal velocity scales as O(Ek(-1/3)), while the meridional circulation is asymptotically smaller by a factor of O(Ek(1/6)).
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geosciences, Multidisciplinary
Alexandre Fournier, Julien Aubert, Vincent Lesur, Guillaume Ropp
Summary: This paper presents a candidate secular variation model for the 13th generation of the International Geomagnetic Reference Field, based on an ensemble of 100 numerical models integrated between 2019.0 and 2025.0. By adjusting 100 different initial conditions extracted from a dynamo simulation to account for the geomagnetic field estimate for 2019.0, the model provides insights into the geomagnetic secular variation up to epoch 2025.0.
EARTH PLANETS AND SPACE
(2021)
Article
Astronomy & Astrophysics
Kiwan Park, Myung-Ki Cheoun
Summary: The article examines the energy spectrum of hot, magnetized, and ionized X-ray emitting plasmas in various regions of the universe through numerical simulations. The results demonstrate the significant influence of magnetic fields on the viscous scale and the unique energy spectrum it yields. Furthermore, the study investigates the spectrum relation between kinetic and magnetic energy, as well as the effect of helical energy on the spectrum steepness.
ASTROPHYSICAL JOURNAL
(2022)
Article
Geochemistry & Geophysics
G. Ropp, V Lesur
Summary: A series of models of the Earth magnetic field and core surface flow have been estimated from 1999 to 2022 using magnetic satellite and ground observatory data. The models show characteristics similar to previous models, but with higher time resolution. Principal component analysis reveals that the largest flow variations occur at high latitudes and under the western part of the Pacific Ocean. Filtering out longer flow variation periods leads to a filtered azimuthal flow with approximately 7-year periodicities propagating westward. These patterns are mainly present at mid- and equatorial latitudes and are compatible with perturbations in the main flow caused by small columnar flows intersecting the core-mantle boundary.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2023)
Article
Geochemistry & Geophysics
L. Sachl, J. Velimsky, J. Fullea, Z. Martinec
Summary: In this paper, a new approach to the inverse problem of global electromagnetic induction is developed and tested, aiming to retrieve the 3-D structure of electrical conductivity in the suboceanic upper mantle using satellite-observed tidal magnetic field. Parametric studies and synthetic tests demonstrate the successful reconstruction of suboceanic upper mantle conductivity structure, with correlation coefficient greater than 0.8 in the ideal noise-free case.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Physics, Fluids & Plasmas
F. Rincon
Summary: The study shows that a transition to a nonlinear state exists at large magnetic Reynolds number, characterized by strong, saturated small-scale magnetohydrodynamic turbulence and a weaker, traveling coherent large-scale field oscillation.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Geochemistry & Geophysics
Christopher J. Davies, Richard K. Bono, Domenico G. Meduri, Julien Aubert, Samuel Greenwood, Andrew J. Biggin
Summary: The researchers investigate the variation of Earth's magnetic field strength over geological time by combining numerical geodynamo simulations with theoretical scaling laws. They find that both scaling laws, despite uncertainties from different heating modes and boundary conditions, are compatible with the power-law behavior exhibited by the internal field and core-mantle boundary fields. The QG-MAC-free scaling matches Earth's modern CMB field, while the QG-MAC-fixed prediction overestimates palaeointensities over the last 3.5 Gyr.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Wolfgang Szwillus, Eldar Baykiev, Yixiati Dilixiati, Joerg Ebbing
Summary: Estimating the depth to magnetic bottom (DTB) is a challenging problem in potential field inversion. Spectral methods, the most popular approach, have been questioned for their reliability. This study proposes a Bayesian approach to estimate susceptibility and DTB from magnetic data using a two-step inversion procedure. The uncertainties due to unknown hyperparameters are rigorously propagated, and pointwise constraints based on heat flow measurements can be easily included. Synthetic tests and application to real data demonstrate the accuracy and applicability of the new algorithm.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Geochemistry & Geophysics
Mariano Fagre, Bruno S. Zossi, Erdal Yigit, Hagay Amit, Ana G. Elias
STUDIA GEOPHYSICA ET GEODAETICA
(2020)
Article
Geosciences, Multidisciplinary
I. Wardinski, D. Saturnino, H. Amit, A. Chambodut, B. Langlais, M. Mandea, E. Thebault
EARTH PLANETS AND SPACE
(2020)
Article
Geochemistry & Geophysics
Filipe Terra-Nova, Hagay Amit
PHYSICS OF THE EARTH AND PLANETARY INTERIORS
(2020)
Article
Astronomy & Astrophysics
Joana Alves Ribeiro, Fernando J. G. Pinheiro, Maria Alexandra Pais
Summary: This study calculated the time-varying geoelectric fields induced in the southern region of Portugal during the strongest geomagnetic storms of solar cycle 24 and presented the first GIC simulations for the country. The susceptibility of the power system network and various factors affecting storms were assessed in the research.
SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS
(2021)
Article
Engineering, Aerospace
Angel O. U. Parentis, Bruno S. Zossi, Hagay Amit, Ana G. Elias
Summary: The study investigates the effects of the Earth's geomagnetic field on the position and area of polar caps and auroral zones. Results show that as the axial degree increases, the total number of polar caps and auroral zones increases, while their total areas exhibit different patterns under various axial field configurations.
ADVANCES IN SPACE RESEARCH
(2021)
Article
Geosciences, Multidisciplinary
P. Alken, E. Thebault, C. D. Beggan, H. Amit, J. Aubert, J. Baerenzung, T. N. Bondar, W. J. Brown, S. Califf, A. Chambodut, A. Chulliat, G. A. Cox, C. C. Finlay, A. Fournier, N. Gillet, A. Grayver, M. D. Hammer, M. Holschneider, L. Huder, G. Hulot, T. Jager, C. Kloss, M. Korte, W. Kuang, A. Kuvshinov, B. Langlais, J. -M. Leger, V. Lesur, P. W. Livermore, F. J. Lowes, S. Macmillan, W. Magnes, M. Mandea, S. Marsal, J. Matzka, M. C. Metman, T. Minami, A. Morschhauser, J. E. Mound, M. Nair, S. Nakano, N. Olsen, F. J. Pavon-Carrasco, V. G. Petrov, G. Ropp, M. Rother, T. J. Sabaka, S. Sanchez, D. Saturnino, N. R. Schnepf, X. Shen, C. Stolle, A. Tangborn, L. Toffner-Clausen, H. Toh, J. M. Torta, J. Varner, F. Vervelidou, P. Vigneron, I. Wardinski, J. Wicht, A. Woods, Y. Yang, Z. Zeren, B. Zhou
Summary: The IAGA V-MOD working group adopted the thirteenth generation of the IGRF in December 2019, which includes definitive main field models for epoch 2015.0 and 2020.0, as well as predictive linear secular variations for 2020.0 to 2025.0. This update provides equations, spherical harmonic coefficients, and maps for magnetic parameters and their predicted changes from 2020.0 to 2025.0.
EARTH PLANETS AND SPACE
(2021)
Article
Geosciences, Multidisciplinary
Hagay Amit, Filipe Terra-Nova, Maxime Lezin, Ricardo I. Trindade
Summary: The South Atlantic Anomaly (SAA) is a region on Earth's surface with a particularly low intensity of the magnetic field. Accurate characterization of the SAA is crucial for understanding core dynamics, geodynamo, and addressing societal issues. Research indicates that the SAA area and center exhibit time dependency, including periods of stability, eastward drift, and rapid southward drift.
EARTH PLANETS AND SPACE
(2021)
Article
Astronomy & Astrophysics
Yvelice Castillo, Maria Alexandra Pais, Joao Fernandes, Paulo Ribeiro, Anna L. Morozova, Fernando J. G. Pinheiro
Summary: The study analyzed the correlations between solar, interplanetary-medium parameters, and geomagnetic-activity proxies, suggesting certain parameters from the TS05 model could be used to explain geomagnetic activity in relation to solar features and IMF condition. An annual oscillation in geomagnetic activity indices was also observed in the 27-day averages.
Article
Astronomy & Astrophysics
D. Saturnino, M. A. Pais, J. Domingos
Summary: The study utilized Principal Component Analysis to process the geomagnetic external field series measured at Virtual Observatories, revealing a first principal mode with dipolar geometry closely following geomagnetic activity levels, and a resolved second principal mode with annual periodicity. These results suggest a possible source for the second mode and indicate the importance of uniform local time sampling in resolving ionospheric structures.
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
(2021)
Article
Geochemistry & Geophysics
I Wardinski, H. Amit, B. Langlais, E. Thebault
Summary: By utilizing MESSENGER probe data, the study infers the internal structure of Mercury's core and suggests that the inner core size ranges from 500 to 660 km, with a corresponding stratified layer thickness of 880 to 500 km. The research provides new insights into the core structure of a planet based on magnetic field observations.
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS
(2021)
Article
Engineering, Electrical & Electronic
Rute Santos, Maria Alexandra Pais, Joana Alves Ribeiro, Joao Cardoso, Luis Perro, Andre Santos
Summary: The influence of shield wires on geoelectric-induced currents (GICs) in power systems is clarified in this study. A simplified power system model, including one transmission line and one shield wire connecting two substations, is used. The Thevenin equivalent circuit, along with the grounding resistances of the substations, is derived to accurately represent the effects of the complete circuit on GICs. The model expands on previous studies by considering the induced voltage along the shield wires and can be applied to relatively short transmission lines.
INTERNATIONAL JOURNAL OF ELECTRICAL POWER & ENERGY SYSTEMS
(2022)
Article
Astronomy & Astrophysics
Joana Alves Ribeiro, Fernando J. G. Pinheiro, Maria Alexandra Pais, Rute Santos, Joao Cardoso, Pedro Baltazar-Soares, Fernando A. A. Monteiro Santos
Summary: The study computes geomagnetically induced currents (GICs) in the power network of mainland Portugal, considering all high voltage lines. A 3D conductivity model for the west region of the Iberian Peninsula is used to reveal the influence of different crustal domains on GIC distribution. GICs are characterized based on significant storms during solar cycle 24, and the highest GICs are found near the transition between geotectonic units. Uncertainties in the conductivity model and grounding resistances are evaluated, and a GIC sensor is installed to validate the model.
SPACE WEATHER-THE INTERNATIONAL JOURNAL OF RESEARCH AND APPLICATIONS
(2023)
Article
Astronomy & Astrophysics
P. Baltazar-Soares, F. J. Martinez-Moreno, J. Alves Ribeiro, F. A. Monteiro Santos, P. Ribeiro, M. A. Pais, A. Mateus, J. Pous
Summary: The first 3D resistivity model for Portugal mainland is reported using data from 31 broadband MT soundings. The model reveals large crustal volumes with contrasting resistivity values and provides important insights into the electrical properties of deep-seated rocks and the structure of the crust.
EARTH AND SPACE SCIENCE
(2023)
Article
Geosciences, Multidisciplinary
Bruno Zossi, Hagay Amit, Mariano Fagre, Ana G. Elias
Summary: This study analyzes the long-term changes in core origin of the auroral zone area utilizing data from the Auroral Boundary Index (ABI) database. By applying a four-step filtering process, the effects of solar activity on the auroral boundary temporal variation are minimized, resulting in consistent observations of area increase/decrease in the northern and southern hemispheres. The comparison between observational evidence and model predictions provides valuable insights into the recent surprising decrease of the auroral zone area.
Article
Geosciences, Multidisciplinary
Anna L. Morozova, Paulo Ribeiro, M. Alexandra Pais
Summary: The Coimbra Magnetic Observatory in Portugal has been providing records of geomagnetic field elements for over 150 years, with researchers homogenizing the measured series of horizontal (H), vertical (Z), and inclination (I) components. The homogenization process upgraded all geomagnetic field elements to the level of 2015.
EARTH SYSTEM SCIENCE DATA
(2021)