Redistributing Earth's Mass

Cazenave, Anny; Nerem, R. S.

doi:10.1126/science.1074593

Cited by 37 publications

(26 citation statements)

References 8 publications

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“…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).…”

mentioning

confidence: 99%

“…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.…”

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confidence: 99%

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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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confidence: 99%

mentioning

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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“…Figure 3 shows a positive jump since late 1997, and 2 J reaches a maximum in 2000. The 1998 anomaly was first detected by Cox et al [15] and subsequently investigated by many researchers [24][25][26]. Dickey et al [24] deduced that it was caused primarily by a recent surge in sub-polar glacial melting and the Pacific Ocean.…”

Section: Long-term Variationmentioning

confidence: 99%

Analysis of the characteristics of the harmonics coefficient J 2 of the Earth’s gravity field in different periods

2012

Chin. Sci. Bull.

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The characteristics of the geopotential coefficient 2 J in different periods are analyzed using satellite laser ranging data spanning the last 27 years. The satellites used in the analysis are Lageos1 and Lageos2. The variations in 2 J are obtained by determining the dynamic orbit. The results show that there are strong seasonal and long-term variations. For different data spans, the seasonal variations agree well in terms of both amplitude and phase. Using all the data, the amplitude and phase of the annual term are 2.5  10 -10 and 127°, respectively, while the amplitude and phase of the semiannual term are 0.94  10 -10 and 213°, respectively. In the case of long-term variation, the secular variation in 2

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“…On the other hand, C 2,0 variations also include seasonal variations mainly due to the displacement of the geophysical fluids at the surface of the Earth (Cazenave and Nerem, 2002). For example, variations in the global atmospheric pressure field leads to such annual and semi-annual effects, especially for the degree 2 of the field (Chao and Eanes, 1995).…”

Section: Introductionmentioning

confidence: 99%

Why the 18.6 year tide cannot explain the change of sign observed in <i>j<sub>2</sub></i>

et al. 2003

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Abstract. Recent studies show a change, starting in 1998, in the behavior of the variation of the dynamical flattening of the Earth (J 2 ), supposed to be constant (secular), and mainly due to the post glacial rebound effect.In this paper, we study to what extent this behavior can be correlated or not with the 18.6 year tide: with more than twenty years of tracking data on LAGEOS-1, that is to say more than a period of 18.6 years, this effect can now be separated from the secular variation.We use our theory of mean orbital motion, dedicated to studies of the long period effects on the orbital motion. We build one single arc of LAGEOS-1 from 1980 to 2002, which provides a continuous description of the orbital parameters. This is the great originality of our approach.We focus our attention on the ascending node of LAGEOS-1, and we show that the change observed inJ 2 cannot be attributed to a statistical error due to a correlation, in short arcs results, between the secular variation of J 2 and the 18.6 year tide. The proof is based on the adjustment of amplitudes and phases of the long period tides, and on the shape of the residuals.

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Redistributing Earth's Mass

Cited by 37 publications

References 8 publications

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

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

Analysis of the characteristics of the harmonics coefficient J 2 of the Earth’s gravity field in different periods

Why the 18.6 year tide cannot explain the change of sign observed in <i>j<sub>2</sub></i>

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Redistributing Earth's Mass

Cited by 37 publications

References 8 publications

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

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

Analysis of the characteristics of the harmonics coefficient J 2 of the Earth’s gravity field in different periods

Why the 18.6 year tide cannot explain the change of sign observed in &lt;i&gt;j&lt;sub&gt;2&lt;/sub&gt;&lt;/i&gt;

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Why the 18.6 year tide cannot explain the change of sign observed in <i>j<sub>2</sub></i>