Geoexploration EIsevier PublisIiing Company, Amsterdam - Printed in the Netherlands 169 Abstracts Session 11: Palaeomagnetic studies THE CAUSE OF THE EARTH’S MAGNETIC FIELD F.E.M. LILLEY Austmlian National University, Canberra, A.C.T. (Australia) (Received February 9, 1971) The earth’s magnetic field originates inside the planet, and there is little doubt that it arises from the material in the core flowing in such a way as to act like an electrical dynamo. Thermal convection in the core, or the precession of the rotating earth, may cause the forces needed to drive the dynamo. The principle of fluid flowing through a magnetic field to cause induced currents which reinforce the field requires a rather special type of flow pattern. The flow pattern in the core is not known, and most effort in the subject has been to find plausible flow patterns which could work. One such pattern is obtained by superimposing distorted cellular convection cells upon a differential rotation in a fluid sphere. The problem of studying the variations of such a dynamo with time, when the mag netic field itself modifies the fluid motion, presents another level of difficulty. However some progress is being made with a numerical approach which steps forward with small increments in time. It is hoped to observe the phenomena of reversals taking place. A NON-STATIONARY MODEL FOR GEOMAGNETIC REVERSALS I.K. CRAIN Australian National University, Canberra, A.C.T. (Australia) (Received February 9, 1971) A series of computer simulations of the earth’s magnetic polarity history have been performed using a non-stationary stochastic model. The earth’s magnetic field is assumed to oscillate regularly in intensity, with constant polarity, until “triggered” into the op- posite polarity by the “random” non-dipole component. This differs from Cox’s earlier stationary model, in that the statistical parameters of the random component are allowed to be time variant. In particular, realizations of the model where the mean and variance of the random component oscillate regularly with time were studied. The earth’s field was taken to be a sinusoidal oscillation of the form: f {A + B [ 1 •t cos(2nr/~, + $,)I } Geoexploration, 9 (1971) 169-173

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Page 1: The cause of the earth's magnetic field

Geoexploration EIsevier PublisIiing Company, Amsterdam - Printed in the Netherlands

169

Abstracts Session 11: Palaeomagnetic studies

THE CAUSE OF THE EARTH’S MAGNETIC FIELD

F.E.M. LILLEY

Austmlian National University, Canberra, A.C.T. (Australia)

(Received February 9, 1971)

The earth’s magnetic field originates inside the planet, and there is little doubt that it arises from the material in the core flowing in such a way as to act like an electrical dynamo. Thermal convection in the core, or the precession of the rotating earth, may cause the forces needed to drive the dynamo.

The principle of fluid flowing through a magnetic field to cause induced currents which reinforce the field requires a rather special type of flow pattern. The flow pattern in the core is not known, and most effort in the subject has been to find plausible flow patterns which could work. One such pattern is obtained by superimposing distorted cellular convection cells upon a differential rotation in a fluid sphere.

The problem of studying the variations of such a dynamo with time, when the mag netic field itself modifies the fluid motion, presents another level of difficulty. However some progress is being made with a numerical approach which steps forward with small increments in time. It is hoped to observe the phenomena of reversals taking place.

A NON-STATIONARY MODEL FOR GEOMAGNETIC REVERSALS

I.K. CRAIN

Australian National University, Canberra, A.C.T. (Australia)

(Received February 9, 1971)

A series of computer simulations of the earth’s magnetic polarity history have been performed using a non-stationary stochastic model. The earth’s magnetic field is assumed to oscillate regularly in intensity, with constant polarity, until “triggered” into the op- posite polarity by the “random” non-dipole component. This differs from Cox’s earlier stationary model, in that the statistical parameters of the random component are allowed to be time variant.

In particular, realizations of the model where the mean and variance of the random component oscillate regularly with time were studied. The earth’s field was taken to be a sinusoidal oscillation of the form:

f {A + B [ 1 •t cos(2nr/~, + $,)I }

Geoexploration, 9 (1971) 169-173