A statistical model of the geomagnetic field

Irving, E.; Ward, M. A.

doi:10.1007/bf00879707

Cited by 64 publications

(40 citation statements)

References 14 publications

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“…One such model is that presented by Irving & Ward (1964). It expresses the latitude dependence of the circular standard deviation of magnetic directions, resulting from a rapidly varying non-dipole component superimposed on a steady axial dipole field.…”

Section: Magnitude Of the Non-dipole Componentmentioning

confidence: 99%

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Non-Dipole Behaviour During an Upper Miocene Geomagnetic Polarity Transition in Oregon

Watkins

1969

Geophysical Journal International

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Summary The palaeomagnetism of a section of 71 successive lavas from southeastern Oregon is presented. A geomagnetic polarity change from reversed to normal polarity which took place during the extrusion of the section 15 million years ago has allowed a palaeomagnetic examination of the non‐dipole field during a period of diminished dipole intensity. During the polarity transition, there existed an apparent easterlydrifting non‐dipole component. Together with an independent determination of the palaeo‐intensity on one lava (Coe 1967) and other recently presented data (Goldstein et al. 1968) an application of Irving & Ward's(1964) geomagnetic field model to the data suggests a maximum dipole intensity as low as two per cent of the present value for a period of not less than 100 years during the transition, outside of which the data are consistent with some present‐day ratios of non‐dipole to dipole field intensity. A very short period of diminished relative dipole intensity occurred during the final stages of the polarity change, when the virtual geomagnetic pole returned to very low latitudes, without any polarity change actually occurring. Because of a great similarity with an independently presented result, it is suggested that this ‘rebound effect’ may reflect a fundamental aspect of the mechanism of at least some polarity changes. Comparison with estimates of the duration of some more recent geomagnetic polarity transitions suggests that the section may have accumulated in less than 50000 years. The lavas of normal polarity, which comprise most of the section, do not show any preferred association with lower or higher oxidation states.

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Section: Magnitude Of the Non-dipole Componentmentioning

confidence: 99%

“…This is a necessary requirement for application of the model, which could not legitimately be applied to a purely dipole behaviour. The application of the data to Irving & Ward's (1964) model is shown diagrammatically in Fig. 9.…”

Section: Magnitude Of the Non-dipole Componentmentioning

confidence: 99%

Non-Dipole Behaviour During an Upper Miocene Geomagnetic Polarity Transition in Oregon

Watkins

1969

Geophysical Journal International

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“…If the field itself is studied, then the variation becomes less as the absolute latitude of the observation is increased [Irving and Ward, 1964]. If, however, VGPs are studied, then the scatter increases as higher absolute latitudes of observation are approached.…”

Section: Introductionmentioning

confidence: 99%

Latitudinal signature of Earth's magnetic field variation over the last 5 million years

Harrison

2009

Geochem Geophys Geosyst

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[1] In order to investigate the latitudinal effect of the geomagnetic field variation, a new data set consisting of virtual geomagnetic poles (VGPs) from all latitudes has been produced. Since the updated data set was limited to data with VGPs within 45°of the geographic poles, data from lava flows with low-latitude VGPs were added. More rigorous criteria were used to winnow the data. The data were divided into groups from different observation latitudes. In each group it was shown that the distribution of VGP latitudes could be described by a predominance of poles (average 82%) following a Fisher distribution with the rest following a distribution that would produce a uniform number of poles as a function of latitude. A distribution composed of two Fisher distributions also fit the data very well. For the case using a Fisher distribution plus a uniform distribution, the Fisher distribution changed such that the angular standard deviation (ASD) of VGPs from a set of observations taken at the equator is about 10°and the ASD at 60°observation latitude is about 19°. These results are similar to some results seeking to determine the ASD of VGPs as a function of observation latitude using other methods, which have been recently published, but there are also discrepancies. The results allow us to model inclination distributions as a function of observation latitude for comparison with data in which only the inclination is known, such as data from drill holes. It is shown that in order not to have doubt about the polarity of the inclination data, a drill hole has to be located at an absolute latitude greater than 27°for there to be less than a 5% error. This has major importance for the location of the ''Mission to the MOHO'' of the Integrated Ocean Drilling Program. The results also confirm that the sources of the nondipole field located in the outer core have to be more than twice as strong at high latitudes than at low latitudes so as to produce the observed increase in VGP scatter with observation latitude. The model of the secular variation proposed here is in no way a theory about how the secular variation happens, but it does allow those who wish to develop such a theory to have a model distribution with which to check their predictions.

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“…The models for secular variation proposed so far aimed mostly at explaining the latitude dependence of angular dispersion of the geomagnetic field, global trend of which is clear and physically meaningful. IRVING and WARD (1964) considered the model A to explain the latitude dependence by the field of a fixed geocentric dipole and randomly oriented nondipole fields with a constant intensity. Model B by CREER et al (1959) is based entirely on a wobble of geocentric dipole.…”

Section: Introductionmentioning

confidence: 99%

Genomagnetic secular variation during the Brunhes epoch inferred from the Paleomagnetism and the last 200 years geomagnetic field.

Tsunakawa

1988

J. geomagn. geoelec

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Paleomagnetic data were compiled from the previous studies on volcanic materials in the southern part of Central Japan to investigate the geomagnetic secular variation during the Brunhes epoch. The distribution of compiled 113 VGPs is examined whether or not the Fisher statistics can be applied. Chi-square test indicates that the hypothesis of uniform azimuthal distribution around a mean VGP, which is assumed in the Fisher statistics, is rejected at a 0.05 significance level. Besides, the VGPs tend to concentrate in a certain direction. Azimuthal distributions of the Brunhes epoch VGPs for other reg01ons, France, the Aleutian Islands, the Canary Islands, Comores Island, Crozet Island, Reunion Island and Amsterdam Island, also show similar elongation and azimuthal uniformity can be rejected for these assemblages. Hence the elongation of VGP distribution appears to be a global characteristic in the Brunhes epoch. These elongations can be explained neither by the westward drift of the nondipole fields, by the wobble of the geocentric dipole, nor by the contortion due to transforming field directions into VGPs. Gauss coefficients of the last 200 years geomagnetic field indicate that several nondipole terms changed linearly with the geocentric axial dipole component of g01. Some of these relationship is possible to have held well not only in the last 200 years but also throughout the Brunhes epoch. In addition, the previous paleointensity studies for the Plio-Pleistocene infer that g01 changed approximately in a normal distribution. On the basis of these results, a new model for the secular variation is proposed, in which the intensity of dipole term g01 changes in a normal distribution and those of the correlating nondipole terms vary linearly with a deviation of g01 from its mean intensity. All combinations of nondipole components are examined and consequently the model with a quadrupole component h12 seems to predict the elongation in azimuthal distribution and the global trend of latitude dependence in angular dispersion. This model appears to have an ability to g01ve a significant and quantitative constraint to the homogeneous dynamo process.

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A statistical model of the geomagnetic field

Cited by 64 publications

References 14 publications

Non-Dipole Behaviour During an Upper Miocene Geomagnetic Polarity Transition in Oregon

Non-Dipole Behaviour During an Upper Miocene Geomagnetic Polarity Transition in Oregon

Latitudinal signature of Earth's magnetic field variation over the last 5 million years

Genomagnetic secular variation during the Brunhes epoch inferred from the Paleomagnetism and the last 200 years geomagnetic field.

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