Analysis of Present Geomagnetic Field for Comparison with Paleomagnetic Results

Abstract

SummaryBoth the dipole and nondipole components of the present geomagnetic field are analyzed by calculating the orientation of hypothetical geocentric dipoles which, if acting alone, would produceThe dispersion in direction of these virtual geomagnetic poles due to the nondipole component of thee geomagnetic field (1) is larger in the southern hemisphere than in the northern; (2) increases with increase in latitude; (3) at all latitudes is of the same order of giagnitude as the dispersion due to a wobble of several tens of degrees of the main geocentric dipole; (4) is anomalously small over a region of continental dimensions in the central Pacific ocean. The parameters describing these variations of poles are transformed to parameters describing variations of the geomagnetic field for comparison with paleomagnetic data.

Non-dipole Field and Fluid Motion in the Earth's Core

“…There is palaeomagnetic evidence that the non-dipole low persisted over a long period of time (Cox and Doell, 1964;Doell and Cox, 1965). Cox (1962) In association with the second view, Runcorn (1964) argued a possibility of a solidified iron layer at the bottom of the mantle under the Pacific area. Cox and Doell (1964) discussed that an electrical conductivity as high as 10-6-10-5e.m.u., which is unlikely for the mantle material, must be assumed in the lower mantle in order to achieve a sufficient shielding, so that the second hypothesis would be far from the truth.…”

Wobbling Motion of the Geomagnetic Dipole Field in Historic Time During These 2000 Years

“…The westward drift of the non-dipole fields relative to the mantle has long been considered to cause the variation of the secular field even without changing the intensity and the direction of the dipole field. Creer (1962) and Cox (1962) have calculated this variation which would be expected to occur at various localities on the earth. The values, however, appear to be a little too small to explain the relatively large amplitude we found in the archaeo-secular variation in the world-wide data.The drifting non-dipole fields may let the individual virtual pole path deviate from the ideal path proposed in this paper, giving rise to each characteristic of the pole motion, but obviously may not be able to change completely the conclusion we have drawn on the motion of the magnetic dipole axis of the fiearth .…”

Geographic Correction of Archeomagnetic Data

“…Here the sample population is the inclination error in the axial dipole methods. That the present geomagnetic field has higher angular dispersion in the southern hemisphere than the northern hemisphere is known already from the many analyses of the 1945 field, for example by Cox (1962) and by Creer (1965). However, these studies also showed a maximum angular dispersion near the equator, which is clearly not the case here.…”