The Magnetic Field of Planet Earth

Hulot, Gauthier; Finlay, Christopher C.; Constable, Catherine; Olsen, Nils; Мандеа, М.

doi:10.1007/978-1-4419-5901-0_6

Cited by 27 publications

(25 citation statements)

References 359 publications

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“…Spatial power spectra for the geomagnetic main field (left) and secular variation (right) models CHAOS4 (Olsen et al, 2014), GUFM1 (Jackson et al, 2000), CALS3k.4 , and CALS10k.1b . the magnetic scalar potential with B = −∇ (e.g., Hulot et al, 2010). The components other than g 0 1 are collectively referred to as the non-axial-dipole (NAD) field, and represent regional departures from an axial dipole field.…”

Section: Introductionmentioning

confidence: 99%

Testing the geocentric axial dipole hypothesis using regional paleomagnetic intensity records from 0 to 300 ka

Ziegler

Constable

2015

Earth and Planetary Science Letters

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Section: Introductionmentioning

confidence: 99%

Testing the geocentric axial dipole hypothesis using regional paleomagnetic intensity records from 0 to 300 ka

Ziegler

Constable

2015

Earth and Planetary Science Letters

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“…Paleointensity data are essential for constraining the conditions in the core (1)(2)(3)(4), for studying the role that the geomagnetic field plays in controlling Earth's atmosphere (5)(6)(7), and as a geochronological tool (8,9). Despite the necessity for a large amount of reliable paleointensity data, there are still significant ambiguities in the available paleointensity information (10)(11)(12); these call for a reevaluation of the existing database (13).…”

mentioning

confidence: 99%

Instability of thermoremanence and the problem of estimating the ancient geomagnetic field strength from non-single-domain recorders

Shaar

Tauxe

2015

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

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Data on the past intensity of Earth's magnetic field (paleointensity) are essential for understanding Earth's deep interior, climatic modeling, and geochronology applications, among other items. Here we demonstrate the possibility that much of available paleointensity data could be biased by instability of thermoremanent magnetization (TRM) associated with non-single-domain (SD) particles. Paleointensity data are derived from experiments in which an ancient TRM, acquired in an unknown field, is replaced by a laboratorycontrolled TRM. This procedure is built on the assumption that the process of ancient TRM acquisition is entirely reproducible in the laboratory. Here we show experimental results violating this assumption in a manner not expected from standard theory. We show that the demagnetization−remagnetization relationship of non-SD specimens that were kept in a controlled field for only 2 y show a small but systematic bias relative to sister specimens that were given a fresh TRM. This effect, likely caused by irreversible changes in micromagnetic structures, leads to a bias in paleointensity estimates.paleomagnetism | paleointensity | thermoremanent magnetization | multidomain T he aim of paleointensity research is to reconstruct variations in the absolute intensity of the ancient geomagnetic field throughout Earth history. Paleointensity data are essential for constraining the conditions in the core (1-4), for studying the role that the geomagnetic field plays in controlling Earth's atmosphere (5-7), and as a geochronological tool (8, 9). Despite the necessity for a large amount of reliable paleointensity data, there are still significant ambiguities in the available paleointensity information (10-12); these call for a reevaluation of the existing database (13).One fundamental problem in paleointensity research arises from the difficulty in locating dateable ancient materials that fulfill the most basic requirement of the absolute paleointensity method. This requirement states that the natural remanent magnetization (NRM) should be a pure thermoremanent magnetization (TRM) carried exclusively by noninteracting singledomain (SD) particles (14). As purely SD materials are rare in nature, much of the published data are based on materials that do not entirely fulfill the strict assumption of pure SD, but still demonstrate a reasonably satisfying relationship between the blocking and unblocking temperatures. That is to say, pseudo SD (PSD) or even small multidomains (MD) are frequently assumed to carry stable and reproducible magnetizations.We first outline the principles of the absolute paleointensity method (14, 15), as most of the data in the paleointensity database rely on some variant of this method (10, 16). The basic underlying assumptions of any absolute paleointensity method are that TRM is quasi-linearly proportional to the intensity of the field (B) in which it was acquired (TRM = α · Β), and that in the absence of chemical and physical alteration, the proportion between the TRM and B is an intrinsic...

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“…When either a surface observatory or a satellite takes a geomagnetic field measurement, this measure is the result of the superposition of many sources (15). The largest contribution generated by the dynamo action within the fluid, iron-rich core of the Earth is known as the core field, with a dominant dipolar component at the Earth's surface.…”

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confidence: 99%

Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields

Mandea

Panet

Lesur

et al. 2012

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

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To understand the dynamics of the Earth's fluid, iron-rich outer core, only indirect observations are available. The Earth's magnetic field, originating mainly within the core, and its temporal variations can be used to infer the fluid motion at the top of the core, on a decadal and subdecadal time-scale. Gravity variations resulting from changes in the mass distribution within the Earth may also occur on the same time-scales. Such variations include the signature of the flow inside the core, though they are largely dominated by the water cycle contributions. Our study is based on 8 y of highresolution, high-accuracy magnetic and gravity satellite data, provided by the CHAMP and GRACE missions. From the newly derived geomagnetic models we have computed the core magnetic field, its temporal variations, and the core flow evolution. From the GRACE CNES/GRGS series of time variable geoid models, we have obtained interannual gravity models by using specifically designed postprocessing techniques. A correlation analysis between the magnetic and gravity series has demonstrated that the interannual changes in the second time derivative of the core magnetic field under a region from the Atlantic to Indian Ocean coincide in phase with changes in the gravity field. The order of magnitude of these changes and proposed correlation are plausible, compatible with a core origin; however, a complete theoretical model remains to be built. Our new results and their broad geophysical significance could be considered when planning new Earth observation space missions and devising more sophisticated Earth's interior models. Earth's interior | core dynamicsO ur planet is a very dynamic system, composed of the core and various layers, such as the mantle, lithosphere, oceans and atmosphere, up to near-Earth space. The fluid core (1), undergoing hydromagnetic motions, contributes to both the origin of the geomagnetic field (2, 3) and the spatial distribution of the Earth's mass (4, 5). Consequently, decadal and subdecadal timescale processes occurring in the core produce signatures in the changes of the geomagnetic (6-8) and gravity (3, 4) fields. To date, short time-scale variations of core origin have only been evidenced in the magnetic field (9-11), and the gravity signals including the signature of the flow inside the core are largely dominated by the water cycle contribution (12). The question that now arises is to what extent core flow effects may be identified in other observables (than magnetic), such as gravity measurements; a core origin has been suggested as a possible cause for rapid geoid flattening variations (13,14).When either a surface observatory or a satellite takes a geomagnetic field measurement, this measure is the result of the superposition of many sources (15). The largest contribution generated by the dynamo action within the fluid, iron-rich core of the Earth is known as the core field, with a dominant dipolar component at the Earth's surface. Sizable contributions come from the static lithospheric field, and e...

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The Magnetic Field of Planet Earth

Cited by 27 publications

References 359 publications

Testing the geocentric axial dipole hypothesis using regional paleomagnetic intensity records from 0 to 300 ka

Testing the geocentric axial dipole hypothesis using regional paleomagnetic intensity records from 0 to 300 ka

Instability of thermoremanence and the problem of estimating the ancient geomagnetic field strength from non-single-domain recorders

Recent changes of the Earth’s core derived from satellite observations of magnetic and gravity fields

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