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Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.


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Journal ArticleDOI
TL;DR: In this paper, a running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure.

128 citations

Journal ArticleDOI
TL;DR: In this paper, it is shown that a zonal fluid motion (zonal toroidal flow in the terminology adopted here) produces rotation of the tesseral magnetic dipole terms and also oscillatory changes in amplitude of these terms.
Abstract: In Part I a method has been developed for the integration of the electromagnetic field equations in the presence of fluid motions in a spherical conductor. This analysis is here applied to an interpretation of the secular geomagnetic variations. A very brief survey of some of the observed features of the secular variation is first given. It is pointed out that not only the phases but also the magnitudes of the harmonic components, including the main dipole, are subject to large changes at the present time. There follows a brief study of the skin effect which indicates that the observed variations of the dipole terms originate in a layer adjacent to the core's boundary several hundred kilometers deep; those of the higher terms originate in a layer no more than 200 km deep. Next, the "coupling matrix" introduced in Part I is evaluated in form of a table of all matrix elements that contain vectors of dipole and quadrupole type but no higher harmonics. It is shown that a zonal fluid motion (zonal toroidal flow in the terminology adopted here) produces rotation of the tesseral magnetic dipole terms and also oscillatory changes in amplitude of these terms. There is one and only one type of matrix element that represents an interaction of the main magnetic dipole with itself; the corresponding fluid motion is a meridional flow (poloidal flow) of quadrupole symmetry. With this term amplification or de-amplification occurs, depending on the sign of the velocity. The theory thus can account for all the observed components of the secular variation.

128 citations

Journal ArticleDOI
01 Jul 1998-Nature
TL;DR: In this paper, a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two North Atlantic sites was performed, showing significant power both at orbital eccentricity (∼100 kyr) and obliquity (41 kyr).
Abstract: More than 20 years ago, on the basis of data from a Pacific sediment core, it was suggested that geomagnetic field intensity may vary with the Earth's orbital obliquity (centred on a period of ∼41 kyr) as a result of the effect of obliquity on precessional forces in the Earth's core1 It had also been proposed that precession plays an important role in the energy budget of the Earth's geodynamo2 But subsequent analyses indicated that the energy available from precession is at least an order of magnitude less than that required to drive the geodynamo3 Here, however, we report a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two North Atlantic sites which shows significant power both at orbital eccentricity (∼100 kyr) and obliquity (41 kyr) The eccentricity power is also present in bulk magnetic properties (such as susceptibility) and is therefore attributable to lithological variations controlled by eccentricity-driven climate change The obliquity power, however, is not apparent in bulk magnetic properties, and seems to be a property of the geomagnetic field itself, thus providing evidence for the orbital forcing of geomagnetic field intensity

128 citations

Journal ArticleDOI
TL;DR: In this paper, an estimate of the ionospheric screening effect is repeated, using a more general solution of Maxwell's equations with parameters chosen to fit the observed features, and it is shown that the modification of the incident electromagnetic field by the ionosphere depends not only on the time scale of the phenomenon but also on the mode and the scale in space of the event, and that a deformation of the magnetosphere by viscous force of the corpuscular stream may be responsible for the preceding reverse change of a sudden commencement.
Abstract: In former estimates of the ionospheric screening effect, a magnetic potential field or an electromagnetic wave has been employed to represent the disturbance field in the neutral atmosphere. But characteristics of a number of changes observed in the geomagnetic field are inconsistent with these special field representations. Hence an estimate of the ionospheric modification is repeated, using a more general solution of Maxwell's equations with parameters chosen to fit the observed features. The result shows that the modification of the incident electromagnetic field by the ionosphere depends not only on the time scale of the phenomenon but also on the mode and the scale in space of the incident field. For changes with a time scale of 10 to 100 seconds and a scale in space of the order of 108 cm, the modification is appreciable on one of the two incident modes. The direction of the magnetic field of this mode significantly rotates during passage through the ionosphere. When this result is applied to the sudden commencement of the magnetic storm it is found that a deformation of the magnetosphere by the viscous force of the corpuscular stream may be responsible for the preceding reverse change of a sudden commencement.

128 citations

Journal ArticleDOI
TL;DR: In this article, the authors improved the description of the evolution of the Sun's open and total magnetic flux on time scales of years to millenia by considering a more rapidly decaying component of the open flux.
Abstract: Aims. We improve the description of the evolution of the Sun’s open and total magnetic flux on time scales of years to millenia. Methods. In the model employed here the evolution of the solar total and open magnetic flux is computed from the flux emerging at the solar surface in the form of bipolar magnetic features, which is related to the sunspot number cycle parameters and can be estimated from historical records. Compared to earlier versions of the model in addition to the long-lived open flux, now also a more rapidly decaying component of the open flux is considered. The model parameters are constrained by comparing its output with observations of the total surface magnetic flux and with a reconstruction of the open magnetic flux based on the geomagnetic indexes. A method to compute the Sun’s total magnetic flux and the sunspot number during the Holocene, starting from the open flux obtained from cosmogenic isotopes records, is also presented. Results. By considering separately a rapidly evolving and a slowly evolving component of the open flux the model reproduces the Sun’s open flux, as reconstructed based on the aa-index, much better and a reasonable description of the radial component of interplanetary magnetic field data is obtained. The greatest improvement is in the reproduction of the cyclic variation of the open flux, including the amplitudes of individual cycles. Furthermore, we found that approximately 25% of the modeled open flux values since the end of the Maunder minimum are lower than the averaged value over 2008, i.e. during the current low minimum. The same proportion is observed in reconstructions of the open flux during the Holocene based on cosmogenic isotopes, which suggests that the present solar minimum conditions are below average, but not exceptional in terms of the heliospheric magnetic flux.

128 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023657
20221,202
2021477
2020553
2019604
2018581