An analysis of the geomagnetic field over the past 2000 years

Hongre, Lionel; Hulot, Gauthier; Khokhlov, A.

doi:10.1016/s0031-9201(97)00115-5

Cited by 171 publications

(173 citation statements)

References 24 publications

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“…Therefore, under the condition of a constant neutral wind velocity, it can be thought that a decrease of the magnetic field intensity due to the secular variation of the Earth's magnetic field [e.g., Bloxham and Gubbins 1985;Hongre et al 1998;Korte and Constable 2011;Nahayo and Kotze 2012;Bhardwaj and Subba Rao 2013] causes a reduction of the Sq amplitude associated with the weakening of the dynamo field. However, because the height-integrated ionospheric conductivity is also affected by the intensity of the magnetic field, the dependence of the Sq amplitude on the magnetic field is more complicated.…”

Section: Introductionmentioning

confidence: 99%

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

et al. 2014

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Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 to 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10-to 12-year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 to 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53% of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 to 2013 and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100-km altitude and residual Sq amplitude showed an anti-correlation for about 71% of the geomagnetic stations. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.

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Section: Introductionmentioning

confidence: 99%

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

et al. 2014

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“…We fitted the PSD by three spectral slopes: f 0 , f À5/3 and f À11/3 . We also estimated the PSD from six published data for illustration: an 800 kyrlong dipole variation model derived from deep sea sediment data (Sint-800) [Guyodo and Valet, 1999] (curve A); a 12 kyr-long dipole variation derived from archeomagnetic data [Yang et al, 2000] (curve B); an 8 kyr-long spherical harmonic model from paleomagnetic data (CALS7K.2) [Korte and Constable, 2005] (curve C); a 2 kyr-long spherical harmonic model from archeomagnetic data [Hongre et al, 1998] (curve D); a spherical harmonic model from historical data (gufm1) [Jackson et al, 2000] (curve E); and recent instrumental observations (IGRF) [Olsen et al, 2005] (curve F). Some of these data were also used by Constable and Johnson [2005].…”

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confidence: 99%

Turbulent structure in Earth's fluid core inferred from time series of geomagnetic dipole moment

Sakuraba

Hamano

2007

Geophysical Research Letters

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[1] The physical grounds are discussed for assessing turbulent structures hidden inside the Earth's liquid core by using a time series of the geomagnetic dipole moment obtained from historical and paleomagnetic data. We propose the idea that the time-averaged wavenumber spectra of electric current density at the core-mantle boundary (CMB) and also velocity near the CMB have relation to the frequency spectrum of the dipole moment. We performed computer simulations of a magnetohydrodynamic spherical dynamo to verify this idea. We show that the frequency spectrum of the dipole moment in the simulation is similar to that inferred by paleomagnetic observations. The simulation results indicate that the underlying kinetic energy spectrum is proportional to m À5/3 in a high wavenumber range, where m is the azimuthal wavenumber. We speculate that a similar turbulent energy spectrum may exist in the Earth's core with a peak near m = 5. Citation: Sakuraba, A., and Y. Hamano (2007), Turbulent structure in Earth's fluid core inferred from time series of geomagnetic dipole moment, Geophys. Res. Lett., 34, L15308,

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“…The non-axial-dipole (NAD) components in the historical field vary on a centennial timescale, and this has been interpreted to indicate similar repeat times in the past (Hulot and Le Mouël, 1994;Hongre et al, 1998). If this is correct, paleointensity records from cores with sedimentation rates less than ~10 cm/k.y.…”

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confidence: 99%

Expedition 306 summary

Kanamatsu¹,

Stein²,

Zarikian³

et al. 2006

Proceedings of the IODP

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The overall aim of the North Atlantic paleoceanography study of Integrated Ocean Drilling Program Expedition 306 is to place late Neogene-Quaternary climate proxies in the North Atlantic into a chronology based on a combination of geomagnetic paleointensity, stable isotope, and detrital layer stratigraphies, and in so doing generate integrated North Atlantic millennial-scale stratigraphies for the last few million years. To reach this aim, complete sedimentary sections were drilled by multiple advanced piston coring directly south of the central Atlantic "ice-rafted debris belt" and on the southern Gardar Drift. In addition to the North Atlantic paleoceanography study, a borehole observatory was successfully installed in a new ~180 m deep hole close to Ocean Drilling Program Site 642, consisting of a circulation obviation retrofit kit to seal the borehole from the overlying ocean, a thermistor string, and a data logger to document and monitor bottom water temperature variations through time.

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An analysis of the geomagnetic field over the past 2000 years

Cited by 171 publications

References 24 publications

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

Turbulent structure in Earth's fluid core inferred from time series of geomagnetic dipole moment

Expedition 306 summary

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