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
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
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
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
William Davis, Bruce Buffett
Summary: Recent studies have shown that time variations in the Earth's axial magnetic dipole field are influenced by both deterministic and random elements, with the slowest decay mode and turbulent diffusion playing key roles. The amplitude and timescale of variations in dipole field generation, including contributions from both velocity and internal magnetic field variations, also have a significant impact on the field's behavior. Applying these findings to the palaeomagnetic field suggests that reversal rates are highly sensitive to changes in the field generation process.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2022)
Article
Astronomy & Astrophysics
Kiwan Park, Myung Ki Cheoun, Chang-Bae Kim
Summary: We have studied the large-scale dynamo forced with helical magnetic energy. The results show that the negative beta effect combined with the Laplacian plays a key role in the dynamo process, rather than the conventional alpha effect. The negative magnetic diffusivity accounts for the attenuation of the plasma kinetic energy in large scales.
ASTROPHYSICAL JOURNAL
(2023)
Article
Geochemistry & Geophysics
Theo Tassin, Thomas Gastine, Alexandre Fournier
Summary: This study examines the impact of double-diffusive convection on magnetic field generation in the liquid outer core of the Earth through 3-D global geodynamo models. The findings suggest that the addition of a second buoyancy source facilitates the onset of convection and the transition between dipole-dominated and multipolar dynamos depends on the nature of the buoyancy forcing. Classical parameters expected to govern this transition fail to capture the dipole breakdown, and instead, a scale-dependent analysis of force balance is necessary to understand the dynamics.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Geochemistry & Geophysics
K. Gwirtz, M. Morzfeld, A. Fournier, G. Hulot
Summary: This study focuses on predicting reversals of Earth's axial magnetic dipole field based on the intensity of the dipole. The prediction strategy varies in skill across different numerical models, serving as an additional criterion to identify Earth-like models. Applying threshold-based predictions to paleomagnetic reconstructions suggests moderate skill in predicting Earth's dynamo over the last two million years.
GEOPHYSICAL JOURNAL INTERNATIONAL
(2021)
Article
Multidisciplinary Sciences
Nikita Balyschew, Artsemi Yushkevich, Vasilii Mikirtumov, Ricardo M. Sanchez, Thiemo Sprink, Mikhail Kudryashev
Summary: This article introduces a cryo-electron tomographic data processing workflow engine called TomoBEAR, which can handle cryo-electron tomographic data in a high-throughput manner, accelerate data processing, and minimize human intervention.
NATURE COMMUNICATIONS
(2023)
Article
Astronomy & Astrophysics
D. Martin-Belda, R. H. Cameron
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(2017)
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Timo Reinhold, Robert H. Cameron, Laurent Gizon
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(2017)
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Astronomy & Astrophysics
R. H. Cameron, M. Schuessler
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(2017)
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D. Martin-Belda, R. H. Cameron
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(2017)
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A. I. Shapiro, S. K. Solanki, N. A. Krivova, R. H. Cameron, K. L. Yeo, W. K. Schmutz
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S. Boro Saikia, C. J. Marvin, S. V. Jeffers, A. Reiners, R. Cameron, S. C. Marsden, P. Petit, J. Warnecke, A. P. Yadav
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(2018)
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Astronomy & Astrophysics
R. H. Cameron, T. L. Duvall, M. Schuessler, H. Schunker
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(2018)
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S. Boro Saikia, C. J. Marvin, S. V. Jeffers, A. Reiners, R. Cameron, S. C. Marsden, P. Petit, J. Warnecke, A. P. Yadav
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(2018)
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Astronomy & Astrophysics
R. H. Cameron, T. L. Duvall, M. Schuessler, H. Schunker
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(2018)
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M. Schuessler, R. H. Cameron
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(2018)
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M. B. Nielsen, L. Gizon, R. H. Cameron, M. Miesch
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(2019)
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H. Schunker, A. C. Birch, R. H. Cameron, D. C. Braun, L. Gizon, R. B. Burston
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(2019)
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R. H. Cameron, M. Schuessler
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(2019)
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S. Jafarzadeh, S. K. Solanki, M. Stangalini, O. Steiner, R. H. Cameron, S. Danilovic
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
(2017)
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Astronomy & Astrophysics
S. Jafarzadeh, S. K. Solanki, R. H. Cameron, P. Barthol, J. Blanco Rodriguez, J. C. del Toro Iniesta, A. Gandorfer, L. Gizon, J. Hirzberger, M. Knoelker, V. Martinez Pillet, D. Orozco Suarez, T. L. Riethmueller, W. Schmidt, M. van Noort
ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES
(2017)