Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

Mandéa, Mioara; Holme, Richard; Pais, Maria Alexandra; Pinheiro, Katia; Jackson, Andrew; Verbanac, Giuliana

doi:10.1007/978-1-4419-7955-1_7

Cited by 96 publications

(53 citation statements)

References 78 publications

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“…[29] From the invoked hypothesis, we have confirmed the presence of all the geomagnetic jerks detected by different authors via different methods [see Mandea et al, 2010]. For example, the 1700/ 1708, 1730/1741, 1750/1763, 1870/1861, 1889/ 1901, 1925/1932 events (each couple XX/YY, XX indicates an event from Alexandrescu et al [1997] and YY from Korte et al [2009], is thought to represent the same event because of the time offset suggested by Korte et al [2009]), have been confirmed by our analysis.…”

Section: Discussionsupporting

confidence: 69%

Geomagnetic jerks as chaotic fluctuations of the Earth's magnetic field

Qamili

Santis

Isac

et al. 2013

Geochem Geophys Geosyst

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[1] The geomagnetic field is chaotic and can be characterized by a mean exponential time scale < t > after which it is no longer predictable. It is also ergodic, so time analyses can substitute the more difficult phase space analyses. Taking advantage of these two properties of the Earth's magnetic field, a scheme of processing global geomagnetic models in time is presented, to estimate fluctuations of the time scale t. Here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks, we propose a method to detect these events over a long time span. This approach considers that epochs characterized by relative minima of fluctuations in time scale t, i.e., those periods when a geomagnetic field is less predictable, are possible jerk occurrence dates. We analyze the last 400 years of the geomagnetic field (covered by the Gufm1 model) to detect minima of fluctuations, i.e., epochs characterized by low values of the time scale. Most of the well known jerks are confirmed through this method and a few others have been suggested. Finally, we also identify some short periods when the field is less chaotic (more predictable) than usual, naming these periods as steady state geomagnetic regime, to underline their opposite behavior with respect to jerks.

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Section: Discussionsupporting

confidence: 69%

Geomagnetic jerks as chaotic fluctuations of the Earth's magnetic field

Qamili

Santis

Isac

et al. 2013

Geochem Geophys Geosyst

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“…One of the most important results from high-resolution satellite geomagnetic field models is how they render geomagnetic jerks, or abrupt discontinuities in the SA of internal origin that have been initially identified in earlier ground observatory records (see e.g. Mandea et al, 2010). The 2003 and 2007 jerks have been related to the existence of a short-lived, intense pulse in the SA energy at the core-mantle boundary (Chulliat et al, 2010b), occurring around 2006 close to the equator.…”

Section: Introductionmentioning

confidence: 99%

Geomagnetic acceleration and rapid hydromagnetic wave dynamics in advanced numerical simulations of the geodynamo

Aubert

2018

Geophysical Journal International

107

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Geomagnetic secular acceleration, the second temporal derivative of Earth's magnetic field, is a unique window on the dynamics taking place in Earth's core. In this study, the behaviours of the secular acceleration and underlying core dynamics are examined in new numerical simulations of the geodynamo that are dynamically closer to Earth's core conditions than earlier models. These new models reside on a theoretical path in parameter space connecting the region where most classical models are found to the natural conditions. The typical time scale for geomagnetic acceleration is found to be invariant along this path, at a value close to 10 years that matches Earth's core estimates. Despite this invariance, the spatio-temporal properties of secular acceleration show significant variability along the path, with an asymptotic regime of rapid rotation reached after 30% of this path (corresponding to a model Ekman number E = 3 10 −7 ). In this regime, the energy of secular acceleration is entirely found at periods longer than that of planetary rotation, and the underlying flow acceleration patterns acquire a two-dimensional columnar structure representative of the rapid rotation limit. The spatial pattern of the secular acceleration at the coremantle boundary shows significant localisation of energy within an equatorial belt. Rapid hydromagnetic wave dynamics is absent at the start of the path because of insufficient time scale separation with convective processes, weak forcing and excessive damping but can be clearly exhibited in the asymptotic regime. This study reports on ubiquitous axisymmetric geostrophic torsional waves of weak amplitude relatively to convective transport, and also stronger, laterally limited, quasi-geostrophic Alfvén waves propagating in the cylindrical radial direction from the tip of convective plumes towards the core-mantle boundary. In a system similar to Earth's core where the typical Alfvén velocity is significantly larger than the typical convective velocity, quasi-geostrophic Alfvén waves are shown to be an important carrier of flow acceleration to the core surface that links with the generation of strong, short-lived and intermittent equatorial pulses in the secular acceleration energy. The secular acceleration time scale is shown to be insensitive to magnetic signatures from torsional waves because of their weak amplitude, and from quasi-geostrophic Alfvén waves because of their intermittent character, and is therefore only indicative of convective transport phenomena that remain invariant along the parameter space path.

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“…The projection from internal wave motions to the SV is rather complicated, as discussed in the context of Earth's fluid core. TWs may contribute to the occurrence of geomagnetic jerks; they cannot however account for all phenomena alone (see [29] for a review). Nevertheless, an increase of spatial and temporal coverage in magnetic data is expected to better resolve the SV and inverted flow models on the top of the metallic region.…”

Section: Concluding Remarks and Discussionmentioning

confidence: 99%

Anelastic torsional oscillations in Jupiter's metallic hydrogen region

Hori

Teed

Jones

2019

Earth and Planetary Science Letters

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We consider torsional Alfvén waves which may be excited in Jupiter's metallic hydrogen region. These axisymmetric zonal flow fluctuations have previously been examined for incompressible fluids in the context of Earth's liquid iron core. Theoretical models of the deep-seated Jovian dynamo, implementing radial changes of density and electrical conductivity in the equilibrium model, have reproduced its strong, dipolar magnetic field. Analyzing such models, we find anelastic torsional waves travelling perpendicular to the rotation axis in the metallic region on timescales of at least several years. Being excited by the more vigorous convection in the outer part of the dynamo region, they can propagate both inwards and outwards. When being reflected at a magnetic tangent cylinder at the transition to the molecular region, they can form standing waves. Identifying such reflections in observational data could determine the depth at which the metallic region effectively begins. Also, this may distinguish Jovian torsional waves from those in Earth's core, where observational evidence has suggested waves mainly travelling outwards from the rotation axis. These waves can transport angular momentum and possibly give rise to variations in Jupiter's rotation period of magnitude no greater than tens of milliseconds. In addition these internal disturbances could give rise to a 10% change over time in the zonal flows at a depth of 3000 km below the surface.

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Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

Cited by 96 publications

References 78 publications

Geomagnetic jerks as chaotic fluctuations of the Earth's magnetic field

Geomagnetic jerks as chaotic fluctuations of the Earth's magnetic field

Geomagnetic acceleration and rapid hydromagnetic wave dynamics in advanced numerical simulations of the geodynamo

Anelastic torsional oscillations in Jupiter's metallic hydrogen region

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