1
Ørsted Results
The perpetually changing geomagnetic field
The geomagnetic field An artists 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
2000 Rapid motion of the geomagnetic pole. The
figure illustrates the motion of the Earths
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 motion Prediction 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 2000 The 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.
Differences between IGRF2000 and DGRF1980 The
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.
DGRF 1980 Definitive Geomagnetic Reference Field
model 1980 The 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.
Differences between DGRF1980 and DGRF1960 The
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.
DGRF 1960 Definitive Geomagnetic Reference Field
model 1960 The 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.
Peter Stauning. Danish Meteorological Institute.
September 2002. pst_at_dmi.dk