Geomagnetic pole

The geomagnetic poles of the earth are in contrast to the actual measured magnetic north and south poles theoretical poles of the earth's magnetic field. They are calculated from the average course of the field lines.

Theoretical models

The original calculation is based on the idea that in the center of the earth, a theoretically infinitely small bar magnet (more precisely, a dipole ) is located. The geomagnetic poles are defined as the intersection of the axis of the bar magnet adopted by the earth's surface. Such a magnet would generate a dipole field, the field lines are circular in rough approximation, with the bar magnet axis and tangent. The axis of this magnetic model migrates over the age of the Earth; at the moment it is at an angle of about 11 ° to the ( rotational) axis of the earth, also known as geographic axis of the earth. Here is the magnetic south pole near the geographic North Pole.

The actual, measurable exactly Earth's magnetic field are equivalent to roughly approximated to that of a dipole. In the dipole model of the earth's magnetism, the actual measurable deviation of the geomagnetic field from a dipole field is explained by the fact that ferromagnetic materials in the globe are unevenly distributed and have different magnetic properties. The dipole field induced in the magnetizable materials magnetic fields. In addition, magnetic material having a magnetic bias from earlier times. The induced and the existing magnetic fields of magnetic material add up to the dipole field so that the field lines are slightly bent near magnetizable material to the dipole field. On the Earth's surface is therefore supported by local variations in field strength and direction relative to the dipole field. However, it is difficult to explain the massive deviations from the dipole field alone with the relatively low occurrence of ferromagnetic materials in the mantle.

In practice, today higher multipoles are taken into account. At regular intervals is determined by measuring the earth's field and modeling the strength and location of multipoles, which, influenced by the measured confounders, would produce as closely as possible the existing magnetic field on the earth. Used here is the current International Geomagnetic Reference Field ( IGRF ), which is published for different time points. This model forms the magnetic field after by an expansion in spherical harmonics.

Origin of the magnetic field structure

The adoption of one or more bar magnet of magnetic material in the center of the earth does not correspond to the actual conditions. While the core of the earth is primarily from iron but this is not ferromagnetic, as the high temperature of the earth's core is far higher than the Curie temperature of iron -nickel alloys. Current models of the geomagnetic field assume that the generating dipoles or multipoles of convection in the outer core are generated.