Gyres, jets and waves in the Earth’s core

Finlay, Christopher C.; Gillet, Nicolas; Aubert, Julien; Livermore, Philip W.; Jault, D.

doi:10.1038/s43017-023-00425-w

Cited by 5 publications

(3 citation statements)

References 179 publications

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“…Our technique uses spatiotemporal variations in the magnetic field to infer compressional flow is analogous with studies of core flow using time-dependent models of Earth's main magnetic field (e.g., Finlay et al, 2020Finlay et al, , 2023Sabaka et al, 2020). Spherical harmonic models of Earth's core magnetic field can provide information about changes in the motion of liquid metal in the outer core through estimates of secular variation.…”

Section: 1029/2023gl105443mentioning

confidence: 99%

Estimating the Ionospheric Induction Electric Field Using Ground Magnetometers

Madelaire,

Laundal,

Hatch

et al. 2024

Geophysical Research Letters

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The ionospheric convection electric field is often assumed to be a potential field. This assumption is not always valid, especially when the ionosphere changes on short time scales min. We present a technique for estimating the induction electric field using ground magnetometer measurements. The technique is demonstrated on real and simulated data for sudden increases in solar wind dynamic pressure of 1 and 10 nPa, respectively. For the real data, the ionospheric induction electric field is 0.15 0.015 mV/m, and the corresponding compressional flow is 2.5 0.3 m/s. For the simulated data, the induction electric field and compressional flow reach 3 mV/m and 50 m/s, respectively. The induction electric field can locally constitute tens of percent of the total electric field. Inclusion of the induction electric field increased the total Joule heating by 2.4%. Locally the Joule heating changed by tens of percent. This corresponds to energy dissipation that is not accounted for in existing models.

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Section: 1029/2023gl105443mentioning

confidence: 99%

Estimating the Ionospheric Induction Electric Field Using Ground Magnetometers

Madelaire,

Laundal,

Hatch

et al. 2024

Geophysical Research Letters

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“…

There has been continuous monitoring of the Earth's magnetic field from satellites over the past two decades, which has refined the modeling of the Earth's main field (MF) and advanced our understanding of the Earth's core dynamics (Finlay et al, 2023). Satellite-data-based geomagnetic field models provide reliable estimates of the global secular variation (SV) and secular acceleration (SA) of the core field, especially for the interannual to decadal variations (Finlay et al, 2020a;Lesur et al, 2022;Ropp et al, 2020).

…”

mentioning

confidence: 99%

“…Nevertheless, many core surface flow models have been derived in the satellite-era using different assumptions, inversion schemes and data set (e.g., Eymin & Hulot, 2005;Gillet et al, 2022;Kloss & Finlay, 2019;Olsen & Mandea, 2008;Pais & Jault, 2008;Ropp & Lesur, 2023;Whaler et al, 2022). These models have revealed very similar large-scale core surface flow structures such as a planetary-scale gyre and a high-latitude jet (Finlay et al, 2023;Holme, 2015), though some details are different.…”

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confidence: 99%

Dynamic Mode Decomposition of the Core Surface Flow Inverted From Geomagnetic Field Models

Li,

Lin,

Zhang

2023

Geophysical Research Letters

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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.

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Radial shear in the flow at the Earth’s core surface

Firsov,

Jault,

Gillet

et al. 2023

Geophysical Journal International

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Summary The Earth’s magnetic field at the core-mantle boundary is the gradient of a harmonic potential function if the mantle is electrically insulating, and the horizontal components of the field can be derived from its radial component in the mantle. Therefore, these components give no further observational information on the core dynamics. However, it can still be envisioned that the horizontal components of the induction equation at Earth’s core surface yield further knowledge on the fluid motions at the top of the core independently of the observations. Here, we show that they provide a linear relationship between the surface velocity and the surface shear (strain shear) that depends on the mantle electrical conductivity. This offers a protocol to calculate the surface shear that we validate with synthetics obtained from dynamo simulations in the limit of a weak mantle conductance. Firstly, using numerical simulations with stress-free boundary condition at the core surface, we retrieve the expected relationship between the horizontal flow uΣ and the shear, ${\bf u}_\Sigma =r\partial _r {\bf u}_{\Sigma }$. Next, we investigate simulations with no-slip boundary condition and insulating mantle, and we obtain the same relationship, even though the shear is not imposed as a boundary condition. Finally, we calculate the flow shear at the top of the core from a magnetic field model based on satellite measurements. The application to geophysical data indicates larger values of the surface flow shear than in the synthetic case, suggesting a possible role of the mantle electrical conductivity. The surface flow shear, in the simulations, much differs from the radial shear in the flow, deeper in the core, which is influenced by the mostly quasi-geostrophic geometry. This implies that we cannot rely on the relationship between the flow and the radial shear for quasi-geostrophic motions to exploit the horizontal components of the induction equation and gain further information on the flow at the Earth’s core surface.

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Gyres, jets and waves in the Earth’s core

Cited by 5 publications

References 179 publications

Estimating the Ionospheric Induction Electric Field Using Ground Magnetometers

Estimating the Ionospheric Induction Electric Field Using Ground Magnetometers

Dynamic Mode Decomposition of the Core Surface Flow Inverted From Geomagnetic Field Models

Radial shear in the flow at the Earth’s core surface

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