The Earth Magnetic Field

It’s the magnetic field that extends from the earth’s interior to where it meets the solaria stream of charged particles emanating from the sun. The magnetic field resembles the field of a large bar magnet near its center or that due to a uniformly magnetized sphere. Its origin is thought to be generated deep down in the earth’s core.

At the surface of the earth, the pole of this equivalent bar magnet, nearest the north geographical pole is actually a south” magnetic pole. This paradoxical situation exists since by convention a north seeking end of a compass needle is defined as pointing north yet must point to a pole of opposite sense or South Pole of the earth’s magnetic field. The flux lines of the field exhibit the usually pattern common to a small magnet as shown below in fig 1.

The direction of the field lines at the equator is horizontal while at the north and south magnetic poles it’s vertical. This geometry is important in interpretation of magnetic anomalies. The earth total field intensity is not perfectly asymmetric about the geographical North Pole e.g. the north magnetic pole in northern Canada is more than 1000miles from the geographical pole.

The earth cannot be exactly represented by a single bar magnet but has numerous higher order poles and very large –scale anomalous features owing to unknown characteristics of the generating mechanism in the earth’s core. As shown in fig 1 the solar wind or constant flux of particles and electric currents from the sun distort the field lines. The deviation from asymmetric field is the anomalous set of features in the earth’s crust caused by local variations in the magnetic minerals and other features which distort the local earth’s magnetic field.

The magnetic field of ...

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...may have been reoriented and because the earth’s field is known to have changed its orientation in geologic and even history time.

Frequently rocks are reversely magnetized hence measurements of this remanent magnetization is a useful aid to interpretation of the rocks which produce an observed anomaly and indeed accessible.

In paleomagnetism and archaeomagnetism, the field particularly depends upon the precise determination of the orientation of the frozen paleo-fields as it is measured in a given rock or other specimen.

Works Cited

APPLICATIONS MANUAL FOR PORTABLE MAGNETOMETERS

By S.BREINER

Geometrics,395 Java Drive

Sunnyvale,California 94086

U.S.A.

SOLID STATE PHYSICS

By S.O.PILAI.

Adapted from ES304 – Geophysical Prospecting, Earth Science Department

University of Melbourne, Australia.

By Dr.Kamar Shah Ariffin.