GRIMM: the GFZ Reference Internal Magnetic Model based on vector satellite and observatory data

Lesur, Vincent; Wardinski, Ingo; Rother, M.; Mandea, Mioara

doi:10.1111/j.1365-246x.2008.03724.x

Cited by 162 publications

(178 citation statements)

References 18 publications

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“…• The GRIMM series from Lesur and co-workers [35,36], from which we use a recent version, GRIMM-3. A similar algorithm using only data from Swarm was used by GFZ to produce the Swarm Level 2 Data Product: Dedicated Inversion [38].…”

Section: Robustness Of Jet Accelerationmentioning

confidence: 99%

An accelerating high-latitude jet in Earth’s core

2016

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Observations of the change in Earth's magnetic field, the secular variation, provide information on the motion of liquid metal within the core that is responsible for its generation. The very latest high-resolution observations from ESA's Swarm satellite mission show intense field change at high-latitude localised in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we explain this feature with a localised, non-axisymmetric, westwards jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core.We find that the jet has increased in magnitude by a factor of three over the period 2000-2016 to about 40 km/yr, and is now much stronger than typical large-scale flows inferred for the core. The current accelerating phase may be a part of a longer term fluctuation of the jet causing both eastwards and westwards movement of magnetic features over historical

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Section: Robustness Of Jet Accelerationmentioning

confidence: 99%

An accelerating high-latitude jet in Earth’s core

2016

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“…Claerbout & Muir 1973;Scales et al 1988;Farquharson & Oldenburg 1998;Tarantola 2005). The L 1 norm measure of misfit has been successfully employed in geomagnetic field modelling of recent and historical data Lesur et al 2008;Finlay et al 2012) and regional archeomagnetic field models (Pavón-Carrasco et al 2009), but it has not previously been tested in the construction of global field models on millennial time scales.…”

Section: Introductionmentioning

confidence: 99%

Limitations in paleomagnetic data and modelling techniques and their impact on Holocene geomagnetic field models

Panovska

Korte

Finlay

et al. 2015

Geophysical Journal International

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S U M M A R YCharacterization of geomagnetic field behaviour on timescales of centuries to millennia is necessary to understand the mechanisms that sustain the geodynamo and drive its evolution. As Holocene paleomagnetic and archeomagnetic data have become more abundant, strategies for regularized inversion of modern field data have been adapted to produce numerous timevarying global field models. We evaluate the effectiveness of several approaches to inversion and data handling, by assessing both global and regional properties of the resulting models. Global Holocene field models cannot resolve Southern hemisphere regional field variations without the use of sediments. A standard data set is used to construct multiple models using two different strategies for relative paleointensity calibration and declination orientation and a selection of starting models in the inversion procedure. When data uncertainties are considered, the results are similar overall regardless of whether we use iterative calibration and reorientation, or co-estimation of the calibration and orientation parameters as part of the inversion procedure. In each case the quality of the starting model used for initial relative paleointensity calibration and declination orientation is crucial and must be based on the best absolute information available. Without adequate initial calibration the morphology of dipole moment variations can be recovered but its absolute value will be correlated with the initial intensity calibrations, an effect that might be mitigated by ensuring an appropriate fit to enough high quality absolute intensity data with low uncertainties. The declination reorientation mainly impacts regional field structure and in the presence of non-zonal fields will result in a non-zero local average. The importance of declination orientation is highlighted by inconsistencies in the West Pacific and Australian sediment records in CALS10k.1b model. Great care must also be taken to assess uncertainties associated with both paleomagnetic and age data and to evaluate the effects of poor data distribution. New consistently allocated uncertainty estimates for sediment paleomagnetic records highlight the importance of adequate uncertainties in the inversion process, as they determine the relative weighting among the data and overall normalized misfit levels which in turn influence the complexity of the inferred field models. Residual distributions suggest that the most appropriate misfit measure is the L 1 norm (minimum absolute deviation) rather than L 2 (least squares), but this seems to have relatively minor impact on the overall results. For future Holocene field modelling we see a need for comprehensive methods to assess uncertainty in individual archeomagnetic data so that these data or models derived from them can be used for reliable initial relative paleointensity calibration and declination orientation in sediments. More work will be needed to assess whether co-estimation or an iterative approach to inversion is more efficient overall...

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“…Applying specifically devised methods, it is possible-globally-to improve from this model our knowledge of the core field and its variations, with a very high resolution in both space and time. The GRIMM models series (17,18) are based on CHAMP satellite data and magnetic observatory hourly means. The GRIMM-3 model, covering the period from 2001 to 2010, describes the core field variations with periods shorter than one year.…”

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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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GRIMM: the GFZ Reference Internal Magnetic Model based on vector satellite and observatory data

Cited by 162 publications

References 18 publications

An accelerating high-latitude jet in Earth’s core

An accelerating high-latitude jet in Earth’s core

Limitations in paleomagnetic data and modelling techniques and their impact on Holocene geomagnetic field models

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

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