The eccentric dipole approximating the Earth's magnetic field

Abstract

The magnetic dipole, situated at the Earth's geometric center O, and whose magnetic field furnishes the best approximation to the observed field of the Earth for the year 1922 has an axis aligned along the direction from a point A (near the geographic South Pole) to the antipodal point B on the Earth's surface, with B situated in latitude 78°.5 north and longitude 291°.2 east. The strength of the dipole is 8.1×1025 Gauss. cm3, yielding a maximal horizontal intensity of 0.315 Gauss at the Earth's surface.If the observed field is to be approximated by that of a magnetic dipole not necessarily situated at the Earth's center, the best approximation (in a sense to be defined) is furnished by a dipole of the same strength as before, and with an axis parallel to AB, the dipole being situated at a point C (magnetic center) 342 km distant from the Earth's center O and in a direction towards a point C′ in latitude 6°.5 north and longitude 161°.8 east. The field of this eccentric dipole is computed by formulae similar to those given by Adolf Schmidt, expressed in tables and charts, and discussed.The approximation of the observed Earth's magnetic field furnished by the eccentric dipole is compared with that furnished by the geometrically centered dipole (uniform magnetization) by discussing the differences, or regional anomalies. The improvement in the approximation due to the shift of the dipole from the geometric center O to the magnetic center C is hardly noticeable for the field in the Northern Hemisphere, but quite distinct in the Southern Hemisphere.