Ørsted ResultsThe perpetually changing geomagnetic field

The geomagnetic fieldAn artist’s concept of the geomagnetic field illustrated by field lines originating from the fluid core of the Earth

Motion of the geomagnetic pole from 1980 to 2000Rapid motion of the geomagnetic pole. The figure illustrates the motion of the Earth’s magnetic poles during the 20 years interval between the Magsat satellite (1979-80) and the Ørsted satellite (1999- ) high-precision geomagnetic measurements. The “dots” indicate the position of the northern dip-pole (vertical magnetic field) in 1980 (blue) and in 2000 (red). The lines illustrate the local compass direction. The pole is moving from the northern islands of Canada into the polar basin. Note the tip of Greenland shown to the right where the location of Thule has been marked.

Prediction of future motionPrediction by two different models of the future motion of the northern pole across the polar basin. Both predictions are probably safe up to year 2005. Thereafter large differences may develop both in the speed of motion and in the direction. So far attempts to model the irregular motions of the poles in the past have failed to reproduce the actual displacements of the poles. Graphics: Nils Olsen.

IGRF2000 International Geomagnetic Reference Field model 2000The model is mainly based on Ørsted magnetic measurements. The world map is shown in a Mollweide projection. The continents have been outlined. Geographic longitudes and latitudes are shown in steps of 30 deg. The color coding indicate the total field strength (scalar field) on a scale from 20,000 to 60,000 nT. The field is strongest at the poles and weakest along magnetic equator. It is particularly weak at the South-Atlantic anomaly region.

DGRF 1980 Definitive Geomagnetic Reference Field model 1980The model is mainly based on Magsat magnetic measurements. The world map is again shown in a Mollweide projection with continents outlined. Geographic longitudes and latitudes are again shown in steps of 30 deg. The scale for color coding is the same as above.

DGRF 1960 Definitive Geomagnetic Reference Field model 1960The model is mainly based on ground-based magnetic measurements. The world map is again shown in a Mollweide projection with continents outlined. The geographical grid and the color scale are the same as above.

Differences between IGRF2000 and DGRF1980The differences between IGRF2000 and DGRF 1980 have been plotted in a Mollweide projection. Geographic longitudes and latitudes are again plotted in steps of 30 deg. The color coding is used to indicate the differences such that blue shades correspond to decreasing field from 1980 to 2000 while yellow-red shades indicate increasing field strength. Note that the color scale spans the range from -2000 nT (i.e. -100 nT/year) to +2000 nT. The total span is thus 1/10 of the scales for the total field in the world maps to the left.

Differences between DGRF1980 and DGRF1960The differences between DGRF1980 and DGRF 1960 have been plotted in a Mollweide projection. Geographic longitudes and latitudes are again plotted in steps of 30 deg. The color coding indicate the differences such that blue shades correspond to decreasing field from 1960 to 1980 while yellow-red shades indicate increasing field strength. Note again that the color scale spans the range from -2000 nT (i.e. -100 nT/year) to +2000 nT. The total span is thus 1/10 of the scales for the total field in the world maps to the left.

Summary: During the – in the life of the Humanity on the Earth – extremely short span of years from 1960 to 2000 (40 years), the geomagnetic field has underwent substantial changes. Some of these are:

● The strength of the magnetic field has decreased in some regions by up to 4000 nT or 10%

● The strength of the magnetic field has in other regions increased by up to 2000 nT or 5 %

● The position of the poles have changed by over 500 km.

● The northern pole is moving rapidly across the polar basin and may reach Russia in 20 years.

Peter Stauning. Danish Meteorological Institute. September 2002. pst@dmi.dk