How do we create a magnetic field

The earth's magnetic field

Magnetic phenomena, in particular the earth's magnetic field, have preoccupied people for ages. The history of navigation would be inconceivable without the compass. We now know that the earth's magnetic field is also an important key to understanding the earth's interior: The course and strength of the magnetic field on the earth's surface and in the outer space of the earth reveal important details about how the “earth dynamo” works inside the earth, the generated the observed magnetic field.

According to current ideas, around 95 percent of the earth's magnetic field is generated by a dynamo effect in the outer, liquid and essentially iron core of the earth. This “earthly” field is superimposed on an “earthly” field, which is generated by electrical currents in the ionosphere and the magnetosphere and makes up barely 5 percent of the total field (see Fig. 1). The earth's magnetic field, together with the atmosphere, offers effective protection against harmful radiation from space, which consists of electrically charged particles.

Representation of the earth's magnetic field with a magnetic dipole

A special geophysical phenomenon that is not yet fully understood is the polarity reversal of the earth's magnetic field, which has occurred frequently and at irregular intervals in the course of the earth's history and is expected to continue. The discovery of polarity reversal goes back to the already mentioned Ocean Drilling Program, in which more or less wide strips of opposite magnetic polarity were found in the drill cores parallel to the mid-ocean ridges where liquid rock material emerges. The magnetic minerals preserved in the strips aligned themselves with the prevailing magnetic field before they solidified and today they show its changing polarity. Such polarity reversals are heralded by minor changes in the magnetic field properties. Observations from the past 150 years show that the strength of the magnetic field has continuously decreased during this time. Satellite measurements during the last two decades also indicate a weakening of the Earth's magnetic field, which in the North Atlantic is around 1 percent per year.

A detailed analysis of the available data suggests that the magnetic field could reverse polarity again within the next 700 to 1000 years. That already has consequences. The observed decrease in the magnetic field strength leads to an increase in radiation from space in the vicinity of the earth. For example, high-flying satellites in regions of low magnetic field strength are already suffering 90 percent of their damage from high-energy particle radiation.

With detailed knowledge of the magnetic field and its temporal changes, there is the prospect of predicting the spatial and temporal behavior of such radiation anomalies and their influence on the environment. Above all, dynamic processes on the sun lead to great magnetic unrest, the so-called magnetic storms, which appear as polar lights at high latitudes and can severely disrupt modern technical facilities such as telecommunications satellites or overland power supply networks. An international initiative tries to predict the "space weather", for which a precise knowledge of the geomagnetic field is necessary.