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
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
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
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
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
Physics, Multidisciplinary
Lorenzo Sironi, Luca Comisso, Ryan Golant
Summary: We investigate the generation and amplification of magnetic fields through the Weibel instability in turbulent plasmas using kinetic particle-in-cell simulations. We find a relationship between the magnetic field strength and the turbulent velocity, as well as the relationship between the magnetic field energy and the turbulent kinetic energy. Our results suggest that turbulence can magnetize collisionless plasmas and create large-scale near-equipartition magnetic fields in the Universe.
PHYSICAL REVIEW LETTERS
(2023)
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
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
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
Mechanics
Kishore Gopalakrishnan, Nishant K. Singh
Summary: This study analytically shows that fluctuations of the mean turbulent kinetic energy at the mesoscale can lead to the growth of a large-scale magnetic field even when the kinetic helicity is zero pointwise. These fluctuations affect turbulent diffusion and turbulent diamagnetism.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Franck Plunian, Thierry Alboussiere
Summary: In the limit of large magnetic Reynolds numbers, a smooth differential rotation can result in fast dynamo action if the electrical conductivity or magnetic permeability is anisotropic. In the case of infinite shear, such as between two rotating solid bodies, the anisotropic dynamo becomes furious, with the magnetic growth rate increasing towards infinity with an increasing magnetic Reynolds number.
JOURNAL OF FLUID MECHANICS
(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
Mechanics
Krzysztof A. Mizerski
Summary: The magnetohydrodynamic (MHD) turbulence is present in both engineering laboratory flows and natural systems. It has the ability to generate and sustain large-scale and small-scale magnetic fields, playing a crucial role in processes such as nuclear fusion energy production. The turbulence also enhances large-scale diffusion and affects the energy and helicity spectra of strongly turbulent flows.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Astronomy & Astrophysics
Pawan Kumar, Bidya Binay Karak, Vindya Vashishth
Summary: The polar magnetic field precursor is considered to be the most robust and physics-based method for predicting the strength of the next solar cycle. The study shows that the memory of the polar field changes from multiple cycles to one cycle with the increase in supercriticality of the dynamo, contradicting existing ideas. Additionally, when the dynamo operates near the critical transition, it produces frequent extended episodes of weaker activity reminiscent of solar grand minima.
ASTROPHYSICAL JOURNAL
(2021)
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
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
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
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
Geosciences, Multidisciplinary
P. Alken, E. Thebault, C. D. Beggan, J. Aubert, J. Baerenzung, W. J. Brown, S. Califf, A. Chulliat, G. A. Cox, C. C. Finlay, A. Fournier, N. Gillet, M. D. Hammer, M. Holschneider, G. Hulot, M. Korte, V. Lesur, P. W. Livermore, F. J. Lowes, S. Macmillan, M. Nair, N. Olsen, G. Ropp, M. Rother, N. R. Schnepf, C. Stolle, H. Toh, F. Vervelidou, P. Vigneron, I. Wardinski
Summary: The 13th revision of the International Geomagnetic Reference Field (IGRF) was released in December 2019, comprising two new main field models and a model of predicted secular variation. These models were produced from candidates submitted by fifteen international teams. The evaluation process, final product derivation approach, and retrospective analysis of the IGRF-12 SV candidates are documented in this study, suggesting potential benefits of combining core modeling with satellite observations for forecasting secular variation.
EARTH PLANETS AND SPACE
(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
Computer Science, Interdisciplinary Applications
Venkatesh Gopinath, Alexandre Fournier, Thomas Gastine
Summary: This article analyzes the behavior of time integrators applied to the semi discrete problem resulting from the spectral discretization of Boussinesq thermal convection equations. Different schemes of various orders are assessed for laminar and turbulent regimes, and it is found that some high-order IMEX-RK methods exhibit occasional order reduction. Comparing with the reference integrator CNAB2, six schemes consistently outperform CNAB2 in terms of accuracy and performance. In the most turbulent setup, 13 IMEX-RK integrators outperform CNAB2 in terms of both accuracy and efficiency.
JOURNAL OF COMPUTATIONAL PHYSICS
(2022)
Article
Geochemistry & Geophysics
K. Gwirtz, T. Davis, M. Morzfeld, C. Constable, A. Fournier, G. Hulot
Summary: This article explores the feasibility of using machine learning techniques to identify precursors of geomagnetic reversals. Through testing with different models and observational records, it is found that the current techniques are not capable of reliably identifying precursors, mainly due to limited data and low frequency resolution.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Multidisciplinary Sciences
Nicolas Gillet, Felix Gerick, Dominique Jault, Tobias Schwaiger, Julien Aubert, Mathieu Istas
Summary: The Earth's magnetic field displays variations on a broad range of time scales. Through satellite monitoring, we have gained more knowledge about the rapid physical processes in the Earth's outer core. We have identified nonaxisymmetric wavelike patterns in the equatorial region of the core surface, which have large spatial scales and interannual periods of approximately 7 years.
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
(2022)
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)
Review
Environmental Sciences
Christopher C. C. Finlay, Nicolas Gillet, Julien Aubert, Philip W. W. Livermore, Dominique Jault
Summary: The turbulent motions of liquid metal in Earth's outer core generate the geomagnetic field. Observations and simulations have shown that the present-day core motions are dominated by a planetary-scale gyre, a jet in the northern polar region, and waves involving the magnetic field. In this review, we explore the dynamics of these core features and discuss their impact on the Earth's magnetism and rotation.
NATURE REVIEWS EARTH & ENVIRONMENT
(2023)
Article
Computer Science, Theory & Methods
Arnau Folch, Claudia Abril, Michael Afanasiev, Giorgio Amati, Michael Bader, Rosa M. Badia, Hafize B. Bayraktar, Sara Barsotti, Roberto Basili, Fabrizio Bernardi, Christian Boehm, Beatriz Brizuela, Federico Brogi, Eduardo Cabrera, Emanuele Casarotti, Manuel J. Castro, Matteo Cerminara, Antonella Cirella, Alexey Cheptsov, Javier Conejero, Antonio Costa, Marc de la Asuncion, Josep de la Puente, Marco Djuric, Ravil Dorozhinskii, Gabriela Espinosa, Tomaso Esposti-Ongaro, Joan Farnos, Nathalie Favretto-Cristini, Andreas Fichtner, Alexandre Fournier, Alice-Agnes Gabriel, Jean-Matthieu Gallard, Steven J. Gibbons, Sylfest Glimsdal, Jose Manuel Gonzalez-Vida, Jose Gracia, Rose Gregorio, Natalia Gutierrez, Benedikt Halldorsson, Okba Hamitou, Guillaume Houzeaux, Stephan Jaure, Mouloud Kessar, Lukas Krenz, Lion Krischer, Soline Laforet, Piero Lanucara, Bo Li, Maria Concetta Lorenzino, Stefano Lorito, Finn Lovholt, Giovanni Macedonio, Jorge Macias, Guillermo Marin, Beatriz Martinez Montesinos, Leonardo Mingari, Genevieve Moguilny, Vadim Montellier, Marisol Monterrubio-Velasco, Georges Emmanuel Moulard, Masaru Nagaso, Massimo Nazaria, Christoph Niethammer, Federica Pardini, Marta Pienkowska, Luca Pizzimenti, Natalia Poiata, Leonhard Rannabauer, Otilio Rojas, Juna Esteban Rodriguez, Fabrizio Romano, Oleksandr Rudyy, Vittorio Ruggiero, Philipp Samfass, Carlos Sanchez-Linares, Sabrina Sanchez, Laura Sandri, Antonio Scala, Nathanael Schaeffer, Joseph Schuchart, Jacopo Selva, Amadine Sergeant, Angela Stallone, Matteo Taroni, Solvi Thrastarson, Manuel Titos, Nadia Tonelllo, Roberto Tonini, Thomas Ulrich, Jean-Pierre Vilotte, Malte Voge, Manuela Volpe, Sara Aniko Wirp, Uwe Woessner
Summary: The EU Center of Excellence for Exascale in Solid Earth (ChEESE) focuses on developing high-level transition capabilities in the geophysics domain to address computational challenges related to earth sciences. The project has successfully optimized community codes and implemented pilot demonstrators to tackle capability and capacity challenges in areas such as seismology, tsunami science, volcanology, and magnetohydrodynamics. The partnership with the Industry and User Board (IUB) has facilitated the dissemination of results across various sectors and institutions.
FUTURE GENERATION COMPUTER SYSTEMS-THE INTERNATIONAL JOURNAL OF ESCIENCE
(2023)
Review
Environmental Sciences
Maylis Landeau, Alexandre Fournier, Henri-Claude Nataf, David Cebron, Nathanael Schaeffer
Summary: Earth's magnetic field is generated by fluid motions, and the mechanism that sustains the geodynamo remains debated. This review assesses the potential mechanisms and finds that convection, possibly aided by the exsolution of light elements, is the most likely scenario.
NATURE REVIEWS EARTH & ENVIRONMENT
(2022)