On the interpretation of virtual geomagnetic pole (VGP) scatter curves

Hulot, Gauthier; Gallet, Yves

doi:10.1016/0031-9201(95)03106-5

Cited by 52 publications

(66 citation statements)

References 20 publications

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“…Although it is unlikely that the two families are completely independent [Hulot and Gallet, 1996;Johnson and Constable, 1996], Model G is nonetheless useful as an approximation. In particular, the model suggests that the equatorial dispersion is dominated by the symmetric geodynamo family.…”

Section: Discussionmentioning

confidence: 99%

Secular variation of the Late Archean–Early Proterozoic geodynamo

Смирнов

Tarduno

2004

Geophysical Research Letters

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We report new paleomagnetic data from ∼2.5 Ga dikes of the Superior Province and derive estimates of paleosecular variation. When combined with data from coeval dikes of the Karelia Craton (Russia) and older (∼2.7 Ga) volcanics of the Pilbara Craton, these estimates suggest a latitudinal variation of secular variation similar to that of the last 5 million years, but with potentially smaller quadrupole family contributions. The observations are consistent with some numerical models of the field that suggest a more dipolar field when the Earth had a much smaller solid inner core.

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Section: Discussionmentioning

confidence: 99%

Secular variation of the Late Archean–Early Proterozoic geodynamo

Смирнов

Tarduno

2004

Geophysical Research Letters

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“…This figure clearly suggests an increase of the VGP scatter with latitude. Although perhaps exaggerated by some possible inclusion of low-quality data (as the recent investigation of Johnson et al 2008 suggests might have been the case, at least to some extent), such a trend brings important information: it shows that the PSV produced by the geodynamo somewhat "senses" the Earth's rotation axis, and breaks the spherical symmetry (Hulot and Gallet 1996). Although this does not come as a surprise, it nevertheless shows that VGP scatter curves can be used to investigate how and how strongly this symmetry is broken.…”

Section: Time-averaged Field and Paleosecular Variation Modelsmentioning

confidence: 93%

“…In particular, and as already mentioned, this formalism predicts that the distribution of field directions will usually not be Fisherian. In contrast VGP scatter, though not strictly Fisherian, can formally (albeit approximately) be related to the variances (σ 2 (g m l ), σ 2 (h m l )) defining the PSV Hulot and Gallet 1996). Figure 18 shows a typical VGP scatter curve for normal polarity lava flow data over the past 5 My.…”

Section: Time-averaged Field and Paleosecular Variation Modelsmentioning

confidence: 96%

The Magnetic Field of Planet Earth

et al. 2010

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The magnetic field of the Earth is by far the best documented magnetic field of all known planets. Considerable progress has been made in our understanding of its characteristics and properties, thanks to the convergence of many different approaches and to the remarkable fact that surface rocks have quietly recorded much of its history. The usefulness of magnetic field charts for navigation and the dedication of a few individuals have also led to the patient construction of some of the longest series of quantitative observations in the history of science. More recently even more systematic observations have been made possible from space, leading to the possibility of observing the Earth's magnetic field in much more details than was previously possible. The progressive increase in computer power was also crucial, leading to advanced ways of handling and analyzing this considerable corpus G. Hulot ( ) G. Hulot et al. of data. This possibility, together with the recent development of numerical simulations, has led to the development of a very active field in Earth science. In this paper, we make an attempt to provide an overview of where the scientific community currently stands in terms of observing, interpreting and understanding the past and present behavior of the so-called main magnetic field produced within the Earth's core. The various types of data are introduced and their specific properties explained. The way those data can be used to derive the time evolution of the core field, when this is possible, or statistical information, when no other option is available, is next described. Special care is taken to explain how information derived from each type of data can be patched together into a consistent description of how the core field has been behaving in the past. Interpretations of this behavior, from the shortest (1 yr) to the longest (virtually the age of the Earth) time scales are finally reviewed, underlining the respective roles of the magnetohydodynamics at work in the core, and of the slow dynamic evolution of the planet as a whole.

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“…For instance, the form of Eq. (2) was deduced from the analysis of a field model for 1965 (McFadden et al, 1988), but recently it was pointed out (Hulot and Gallet, 1996) that this cannot match even the field of recent past (e.g. 1800), and so justification for using Eq.…”

Section: Introductionmentioning

confidence: 99%

“…These conventional models, therefore, relied on some ad hoc postulates about the latitude dependence of a component of the model, that has no firm quantitative basis. Also, because predictions of other aspects of the magnetic field were difficult, most of the observed data (other than the scatter of VGPs) were not fully utilized for substantiating these models, though there have been some studies devoted to this direction (Merrill and McElhinny, 1983;Shibuya et al, 1995;Hulot and Gallet, 1996).…”

Section: Introductionmentioning

confidence: 99%

Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients.

Kono¹

1997

J. geomagn. geoelec

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Expressions are derived for the magnetic field directions produced by randomly varying Gauss coefficients. This approach was pioneered by Constable and Parker (1988), and followed by Kono and Tanaka (1995) and Kono and Hiroi (1996). The present treatment is a sequel to the latter two. The basic assumption is that the magnitude of the axial dipole component is much larger than all the other terms: equatorial dipoles or nondipole components. It is also assumed that, in a sufficiently long time interval, Gauss coefficients, g' and h7 , behave as independent random variables that have the first and second moments defined. General expressions are obtained for the field directions (inclination I and declination D). Paleosecular variation (PSV) of field directions is formulated as latitude dependences of statistical parameters (the means and variances) of inclination and declination.It is possible to derive a family of PSV models by specifying the statistical nature of individual Gauss coefficients, i.e., assigning means and variances to them. In this paper, we describe a "homogeneous background model" (HBM), which consists of a large axial dipole component (g°) and other harmonics that have zero mean and variances decreasing exponentially with the degree of the harmonic. This model is too homogeneous to reproduce observed latitudinal variation of secular variation, but is quite useful to identify the harmonics that have effect that is larger than produced by the HBM. Comparison with paleomagnetic data obtained from volcanic rocks of 0-5 Ma ages (Quidelleur et al., 1994) shows that it is necessary that the mean of ga must be about 5% of the mean of go, and that g2 (or h2) should have about three to four times as large an effect as suggested by the HBM. The former conclusion is consistent with the result of Constable and Parker (1988), while the latter conclusion substantiates the similar conclusion obtained by Kono and Tanaka (1995) by the analysis of the scatter of the virtual geomagnetic poles (VGPs).

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On the interpretation of virtual geomagnetic pole (VGP) scatter curves

Cited by 52 publications

References 20 publications

Secular variation of the Late Archean–Early Proterozoic geodynamo

Secular variation of the Late Archean–Early Proterozoic geodynamo

The Magnetic Field of Planet Earth

Paleosecular Variation in Field Directions Due to Randomly Varying Gauss Coefficients.

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