Latitude Dependence of the Angular Dispersion of the Geomagnetic Field

Cox, Allan

doi:10.1111/j.1365-246x.1970.tb06069.x

Cited by 273 publications

(264 citation statements)

References 14 publications

Supporting

Mentioning

251

Contrasting

Unclassified

Order By: Relevance

“…Although I and k can be used to compare different segments of the KM-3 record, it is the angular dispersion of poles (33 that is used to compare individual SV records with global averages of field behavior. This was done following Cox [1970] assuming that the poles are Fisherian distributed.…”

Section: Discussionmentioning

confidence: 99%

A detailed record of paleomagnetic field change from Searles Lake, California: 1. Long‐term secular variation bounding the Gauss/Matuyama polarity reversal

Glen¹,

Liddicoat²,

Coe³

1999

J. Geophys. Res.

View full text Add to dashboard Cite

Clement, 1992] intimates that the field may commonly show signs of early instability. This precursory event is actually one of a sequence of oscillations (in inclination and intensity) preceding the transition. That these fluctuations occur at roughly 4 kyr intervals leading up to the reversal (which also appears at this same interval) strongly suggests that an oscillatory disturbance in the core, active over at least 15 kyr prior to the transition, had eventually triggered the reversal. In addition, that these waveforms are absent from the postransitional record suggests the reversal process actively rejuvenates and stabilizes the field.

show abstract

Section: Discussionmentioning

confidence: 99%

A detailed record of paleomagnetic field change from Searles Lake, California: 1. Long‐term secular variation bounding the Gauss/Matuyama polarity reversal

Glen¹,

Liddicoat²,

Coe³

1999

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…The angular standard deviation of poles (ASD) has often been used to monitor paleosecular variation [Cox, 1970] …”

Section: Comparison With Earlier Studymentioning

confidence: 99%

Paleomagnetic directions and K/Ar dating of 0 to 1 Ma lava flows from La Guadeloupe Island (French West Indies): Implications for time‐averaged field models

Carlut¹,

Quidelleur²,

Courtillot³

et al. 2000

J. Geophys. Res.

View full text Add to dashboard Cite

Abstract. Twenty-six lava flows spanning the last million years were sampled in La Guadeloupe, French West Indies. Because of the lack of continuous volcano-stratigraphic sections in La Guadeloupe, dating is necessary in order to describe the temporal evolution of the geomagnetic field in this time interval. New K/Ar ages ranging from 50 ka to I Ma have been obtained on andesires using the Cassignol-Gillot technique at the Universitd Paris Sud -Institut de Physique du Globe de Paris Orsay laboratory. Additional flows (with K/At ages obtained using the same dating technique) were also sampled for paleomagnetic investigations. More than 200 samples were analyzed using both alternating field AF and thermal stepwise demagnetization techniques. Duplicate samplings of two flows at three different sites demonstrate that within-How dispersion is negligible for the andesitic lava flows sampled in this study. Direct comparison with an earlier paleomagnetic study performed on the island indicates that, for the three investigated flows, modern demagnetization techniques yield much better defined paleomagnetic directions. The MatuyamaBrunhes transition was recorded in a three-flow section and is dated at 781 + 18 ka, in good agreement with other recent radiometric age determinations. The mean paleomagnetic pole calculated from the 23 normal polarity flows is indistinguishable t¾om geographic north, which implies that no significant persistent axial quadrupole term can be identified at this site for the last million years. This result contradicts earlier results and has important implications for models of the time-averaged field (TAF). An Occam algorithm was used to construct a TAF model from the global volcanic database from the last 5 Ma. Substitution of the mean direction calculated from the earlier study for the Lesser Antilles by our new mean value reduces the quadrupole term by more than 30•. This effect, which was produced by changing data from a single site, demonstrates that older paleomagnetic sites may need to be reinvestigated. Furthermore, it also highlights the limitations of TAF models that can be inferred from paleomagnetic databases in their present state.

show abstract

“…Cox (1962) and CREER (1962) proposed the model C including the dipole wobble and nondipole fields on the basis of the present field. Cox (1970) provided the model D in which the latitude dependence of angular dispersions is induced by a wobble of geocentric dipole, sinusoidal oscillation of its intensity, and nondipole fields oriented randomly with variable intensities. MCELHINNY and MERRILL (1975) compiled the world-wide data and provided further discussion on the latitude dependence of angular dispersion during the past 5 Ma.…”

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

View full text Add to dashboard Cite

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.

show abstract

Latitude Dependence of the Angular Dispersion of the Geomagnetic Field

Cited by 273 publications

References 14 publications

A detailed record of paleomagnetic field change from Searles Lake, California: 1. Long‐term secular variation bounding the Gauss/Matuyama polarity reversal

A detailed record of paleomagnetic field change from Searles Lake, California: 1. Long‐term secular variation bounding the Gauss/Matuyama polarity reversal

Paleomagnetic directions and K/Ar dating of 0 to 1 Ma lava flows from La Guadeloupe Island (French West Indies): Implications for time‐averaged field models

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

Contact Info

Product

Resources

About