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/s11214-010-9663-x

Cited by 125 publications

(72 citation statements)

References 79 publications

(99 reference statements)

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“…Therefore, the behavior of geomagnetic field has significant potential to yield insight into Earth's geodynamics, such as the influence of core-mantle interactions Bloxham, 2000), changes in outer-core flow and geomagnetic jerks (Bloxham et al, 2002;Dumberry and Finlay, 2007;Mandea et al, 2010;Olsen and Mandea, 2008). Besides the geodynamic significance, connections between the geomagnetic field and global climate have been suggested (Courtillot et al, 2007;Gallet et al, 2005;Kent, 1982), but these claims remain controversial (Bard and Delaygue, 2008).…”

Section: Introductionmentioning

confidence: 99%

Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China

Cai

Tauxe

Deng

et al. 2014

Earth and Planetary Science Letters

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In this study, we have carried out paleointensity experiments on 918 specimens spanning the last ∼7 kyr, including pottery fragments, baked clay and slag, collected from Shandong, Liaoning, Zhejiang and Hebei Provinces in China. Approximately half of the specimens yielded results that passed strict data selection criteria and give high-fidelity paleointensities. The virtual axial dipole moments (VADMs) of our sites range from ∼2 × 10 22 to ∼13 × 10 22 Am 2 . At ∼2250 BCE our results suggest a paleointensity low of ∼2 × 10 22 Am 2 , which increases to a high of ∼13 × 10 22 Am 2 by ∼1300 BCE. This rapid (less than 1000 yrs) six-fold change in the paleointensity may have important implications for the dynamics of core flow at this time. Our data from the last ∼3 kyr are generally in good agreement with the ARCH3k.1 model, but deviate significantly at certain time periods from the CALS3k.4 and CALS10k.1b model, which is likely due to differences in the data used to constrain these models. At ages older than ∼3 ka, where only the CALS10k.1b model is available for comparison, our data deviate significantly from the model. Combining our new results with the published data from China and Japan, we provide greatly improved constraints for the regional model of Eastern Asia. When comparing the variations of geomagnetic field in three global representative areas of Eastern Asia, the Middle East and Southern Europe, a common general trend of sinusoidal variations since ∼8 ka is shown, likely dominated by the dipole component. However, significant disparities are revealed as well, which we attribute to non-dipolar components caused by movement of magnetic flux patches at the core-mantle boundary.

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Section: Introductionmentioning

confidence: 99%

Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China

Cai

Tauxe

Deng

et al. 2014

Earth and Planetary Science Letters

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“…Mandea et al, 2010), whose occurrence has been impeding a more efficient prediction at decadal timescale (Maus et al, 2008;Beggan and Whaler, 2010).…”

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confidence: 99%

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

2014

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Abstract. The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) inPortugal has a long history of observation of the geomagnetic field, spanning almost 150 yr since the first geomagnetic measurements in 1866. These long instrumental geomagnetic records provide very important information about variability of geomagnetic elements and indices, their trends and cycles, and can be used to improve our knowledge on the sources that drive variations of the geomagnetic field: liquid core dynamics (internal) and solar forcing (external).However, during the long life of the Coimbra Observatory, some inevitable changes in station location, instrument's park and electromagnetic environment have taken place. These changes affected the quality of the data collected at COI causing breaks and jumps in the series of geomagnetic field components and local K index. Clearly, these inhomogeneities, typically shift-like (step-like) or trend-like, have to be corrected or, at least, minimized in order for the data to be used in scientific studies or to be submitted to international databases.In this study, the series of local K index and declination of the geomagnetic field are analysed: the former because it allows direct application of standard homogenization methods and the latter because it is the longest continuous series produced at COI. For the homogenization, visual and statistical tests (e.g. standard normal homogeneity test) have been applied directly to the local geomagnetic K index series (from 1951 to 2012). The homogenization of the monthly averages of declination (from 1867 to 2012) has been done using visual analysis and statistical tests applied to the time series of the first differences of declination values, as an approximation to the first time derivative. This allowed not only estimating the level of inhomogeneity of the studied series but also detecting the highly probable homogeneity break points. These points have been cross-checked with the metadata, and the COI series have been compared with reference series from the nearest geomagnetic stations and, in the case of declination series, from the recent geomagnetic field model COV-OBS to set up the required correction factors. As a result, the homogenized series measured in COI are considered to be essentially free of artificial shifts starting from the second half of the 20th century, and ready to be used by the scientific community.

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“…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)(10)(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).…”

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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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Geomagnetic Jerks: Rapid Core Field Variations and Core Dynamics

Cited by 125 publications

References 79 publications

Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China

Geomagnetic intensity variations for the past 8 kyr: New archaeointensity results from Eastern China

Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal

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

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