Rapid Variations of Earth’s Core Magnetic Field

Lesur, Vincent; Gillet, Nicolas; Hammer, Magnus D.; Mandea, Mioara

doi:10.1007/s10712-021-09662-4

Cited by 32 publications

(28 citation statements)

References 152 publications

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“…The two decades covered by satellite data limit the period range where flow models are best resolved to time scales shorter than 10 y. Within this subdecadal range, a spectral line at

y has been isolated in ground-based series recorded in the vicinity of the equator ( 5 ). To focus on the source of this interannual signal, we band-pass filter the obtained flow models for periods between 4 and 9.5 y, with an order 4 causal Butterworth filter.…”

Section: Methodsmentioning

confidence: 99%

“…Recently, the existence of a broad spectral peak centered on a period of

y has been isolated in some observatory series recorded at low latitudes (figure 3 of ref. 5 ). This enables us to gain insight into geomagnetic field fluctuations at the core surface, on time scales close to T A and at large length scales (typically spherical harmonic degrees

).…”

Section: Introductionmentioning

confidence: 99%

“…This enables us to gain insight into geomagnetic field fluctuations at the core surface, on time scales close to T A and at large length scales (typically spherical harmonic degrees

). At shorter periods (

y), we struggle to separate the magnetic field originating in the core from the ionospheric and magnetospheric fields ( 5 ).…”

Section: Introductionmentioning

confidence: 99%

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Satellite magnetic data reveal interannual waves in Earth’s core

Gillet

Jault

Aubert

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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Significance The physics responsible for most of the interannual geomagnetic field changes, continually recorded by satellites for 20 years, is a long-standing open issue. By analyzing magnetic data, we detect Magneto–Coriolis waves in the Earth’s outer core that account for a significant part of this signal. We further propose theoretical advances in the physical characterization of these waves, enabling a deeper understanding of the dynamics behind the geomagnetic signal. It should allow one to better sketch the heterogeneous magnetic field deep within the core, shedding further light on the mechanisms that sustain the geodynamo. Our interpretation does not require the presence of a stratified layer at the top of the core, with potent consequences regarding the Earth’s thermal history.

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“…The two decades covered by satellite data limit the period range where flow models are best resolved to time scales shorter than 10 y. Within this subdecadal range, a spectral line at

Section: Methodsmentioning

confidence: 99%

“…Recently, the existence of a broad spectral peak centered on a period of

).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Satellite magnetic data reveal interannual waves in Earth’s core

Gillet

Jault

Aubert

et al. 2022

Proc. Natl. Acad. Sci. U.S.A.

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“…By 'large', it is meant that the changes exceed the typical amplitude of accelerations observed over decadal and longer periods (e.g. Lesur et al 2022).…”

mentioning

confidence: 99%

“…Local time sampling by polar orbiting satellites, and most notably the difficulties of separating internal and external geomagnetic signals currently limit the temporal resolution at which the acceleration can be retrieved down to about a year (e.g. Lesur et al 2022). The respective temporal and spatial resolution advantages of observatory and satellite data are therefore best exploited when the two sources of data are used in conjunction, as has been done after 1999 in global field models such as the CHAOS series (most recently Finlay et al 2020).…”

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confidence: 99%

A taxonomy of simulated geomagnetic jerks

Aubert

Livermore

Finlay

et al. 2022

Geophysical Journal International

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SUMMARY Geomagnetic jerks—abrupt changes in the acceleration of Earth’s magnetic field that punctuate geomagnetic records— have been richly documented over the past decades by taking advantage of the complementary strengths of ground observatory and satellite measurements. It has recently been proposed that these events originate from the interplay and timescale separation between slow convection and rapid hydromagnetic wave propagation in Earth’s outer core, with these latter waves playing a key role in the generation of jerk signals. To assess the generality of this explanation, here we analyse a catalogue of 14 events obtained during a 14 000-yr-long temporal sequence from a numerical geodynamo simulation that is the closest to date to Earth’s core conditions regarding timescale separation. Events are classified according to their dynamic origin and the depth at which they are triggered in the outer core. The majority of jerk events are found to arise from intermittent local disruptions of the leading-order force balance between the pressure, Coriolis, buoyancy and Lorentz forces (the QG-MAC balance), that leads to an inertial compensation through the emission of rapid, non-axisymmetric, quasi-geostrophic Alfvén waves from the region where this force balance is disrupted. Jerk events of moderate strength arise from the arrival at low latitudes at the core surface of hydromagnetic wave packets emitted from convective plumes rooted at the inner core boundary. As in an earlier simulation, these account well for jerk features that have recently been documented by satellite and ground observations. The more realistic timescales in the simulation reported here allow further details to be distinguished, such as multiple temporal alternations of geomagnetic acceleration pulses at low latitudes, long-range synchronization of pulse foci in space and rapid longitudinal drift of these foci at the core surface. The strongest events in the catalogue arise from disruption of the leading-order force balance near or at the core surface, from the combined influence of the arrival of buoyancy plumes and magnetic field rearrangement. The hydromagnetic waves that are sent laterally and downwards generate signals that clearly illustrate the presence of nearly synchronous ‘V-shaped’ magnetic variation patterns over a wide portion of Earth’s surface and also at mid to high latitudes, despite the source being confined to low latitudes at the core surface. Other well-known characteristics of strong geomagnetic jerks such as surges in the intensity of the secular variation and inflexions in the length-of-day variations are also reproduced in these events. Irrespectively of the event strength, our results support the hypothesis of a single physical root cause—the emission of magneto-inertial waves following a disruption of the QG-MAC balance—for jerks observed throughout the geomagnetic record.

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Temporal Evolution: Geomagnetic Jerks

Mandéa

2022

SpringerBriefs in Earth Sciences

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Rapid Variations of Earth’s Core Magnetic Field

Cited by 32 publications

References 152 publications

Satellite magnetic data reveal interannual waves in Earth’s core

Satellite magnetic data reveal interannual waves in Earth’s core

A taxonomy of simulated geomagnetic jerks

Temporal Evolution: Geomagnetic Jerks

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