The Earth is associated with the geomagnetic field that has
an S (N) -pole of a magnet near the North (South) Pole.
A magnetic compass, therefore, approximately points toward the north.
However, the pointing direction is slightly different from
the true north by an angle called "declination".
Also, two pairs of poles can be defined for the geomagnetic field:
the geomagnetic poles and the magnetic poles.
The magnetic north corresponds to neither pole,
since the geomagnetic field actually has a more complicated shape
than a magnetic field generated by a bar magnet (See below).
Moreover, a magnetic needle suspended at a center of balance does not
keep horizontal.
As a rule, the N-pole dips downward by an angle called "inclination"
in the northern hemisphere.
If we rotate a compass
for southern hemisphere in Japan... (MPG:2.3MB)
The Geomagnetic poles (dipole poles)
are the intersections of the Earth's surface
and the axis of a bar magnet hypothetically placed at the center
the Earth by which we approximate the geomagnetic field.
There is such a pole in each hemisphere, and the poles are called as
"the geomagnetic north pole" and "the geomagnetic south pole",
respectively.
On the other hand,
the magnetic poles are the points
at which magnetic needles become vertical.
There also are "the magnetic north pole" and "the magnetic south pole".
The geomagnetic or magnetic south (north) poles correspond to
the N (S) -pole of a magnet.
In Table 1
and Figure 1
, we show predicted locations of
the geomagnetic and magnetic poles by "International Geomagnetic Reference Field"
(IGRF-11) from 1900 through 2015.
These poles are drifting according to slow and smooth change
in the geomagnetic field called "the geomagnetic secular variation".
In Figure 2, we show the predicted
declination at Kyoto in 2010 by IGRF-11 in addition to the predicted
directions towards the geomagnetic and magnetic north poles.
The reason why we have now westward declination in Japan is
probably due to the presence of a strong positive geomagnetic anomaly
around Lake Baikal in Siberia.
The N-poles of magnetic needles tend to be attracted to the anomaly
to show westward declinations around Japan.
Model field by IGRF
Animation of secular variation in geomagnetic
total intensity for the last 400 years.
|
Year |
North geomagnetic pole |
South geomagnetic pole | North magnetic pole |
South magnetic pole |
Dipole moment 1022Am2 |
Lat. | Long. |
Lat. | Long. |
Lat. | Long. |
Lat. | Long. |
1900 | 78.6N | 68.8W | 78.6S | 111.2E | 70.5N | 96.2W | 71.7S | 148.3E | 8.32 |
1905 | 78.6N | 68.7W | 78.6S | 111.3E | 70.7N | 96.5W | 71.5S | 148.6E | 8.30 |
1910 | 78.6N | 68.7W | 78.6S | 111.3E | 70.8N | 96.7W | 71.2S | 148.7E | 8.27 |
1915 | 78.6N | 68.6W | 78.6S | 111.4E | 71.0N | 97.0W | 70.8S | 148.5E | 8.24 |
1920 | 78.6N | 68.4W | 78.6S | 111.6E | 71.3N | 97.4W | 70.4S | 148.2E | 8.20 |
1925 | 78.6N | 68.3W | 78.6S | 111.7E | 71.8N | 98.0W | 70.0S | 147.6E | 8.16 |
1930 | 78.5N | 68.3W | 78.5S | 111.7E | 72.3N | 98.7W | 69.5S | 147.0E | 8.13 |
1935 | 78.5N | 68.4W | 78.5S | 111.6E | 72.8N | 99.3W | 69.1S | 145.8E | 8.11 |
1940 | 78.5N | 68.5W | 78.5S | 111.5E | 73.3N | 99.9W | 68.6S | 144.6E | 8.09 |
1945 | 78.5N | 68.5W | 78.5S | 111.5E | 73.9N | 100.2W | 68.2S | 144.5E | 8.08 |
1950 | 78.5N | 68.8W | 78.5S | 111.2E | 74.6N | 100.8W | 67.9S | 143.6E | 8.06 |
1955 | 78.5N | 69.2W | 78.5S | 110.8E | 75.2N | 101.4W | 67.2S | 141.5E | 8.05 |
1960 | 78.5N | 69.5W | 78.5S | 110.5E | 75.3N | 101.0W | 66.7S | 140.2E | 8.03 |
1965 | 78.5N | 69.9W | 78.5S | 110.1E | 75.6N | 101.3W | 66.3S | 139.5E | 8.00 |
1970 | 78.6N | 70.2W | 78.6S | 109.8E | 75.9N | 101.0W | 66.0S | 139.4E | 7.97 |
1975 | 78.7N | 70.5W | 78.7S | 109.5E | 76.2N | 100.7W | 65.7S | 139.5E | 7.94 |
1980 | 78.8N | 70.8W | 78.8S | 109.2E | 76.9N | 101.7W | 65.4S | 139.3E | 7.91 |
1985 | 79.0N | 70.9W | 79.0S | 109.1E | 77.4N | 102.6W | 65.1S | 139.1E | 7.87 |
1990 | 79.1N | 71.1W | 79.1S | 108.9E | 78.1N | 103.7W | 64.9S | 138.9E | 7.84 |
1995 | 79.3N | 71.4W | 79.3S | 108.6E | 79.0N | 105.2W | 64.8S | 138.7E | 7.81 |
2000 | 79.5N | 71.6W | 79.5S | 108.4E | 81.0N | 109.7W | 64.7S | 138.4E | 7.79 |
2005 | 79.7N | 71.8W | 79.7S | 108.2E | 83.1N | 117.8W | 64.5S | 137.8E | 7.77 |
2006 | 79.8N | 71.9W | 79.8S | 108.1E | 83.8N | 122.0W | 64.5S | 137.7E | 7.76 |
2007 | 79.9N | 72.0W | 79.9S | 108.0E | 84.0N | 123.2W | 64.5S | 137.6E | 7.76 |
2008 | 79.9N | 72.0W | 79.9S | 108.0E | 84.2N | 124.9W | 64.5S | 137.6E | 7.75 |
2009 | 80.0N | 72.1W | 80.0S | 107.9E | 84.9N | 131.0W | 64.5S | 137.5E | 7.75 |
2010 | 80.0N | 72.2W | 80.0S | 107.8E | 85.0N | 132.6W | 64.4S | 137.3E | 7.75 |
2011 | 80.1N | 72.3W | 80.1S | 107.7E | 85.1N | 134.0W | 64.4S | 137.2E | 7.74 |
2012 | 80.1N | 72.4W | 80.1S | 107.6E | 85.9N | 147.0W | 64.4S | 137.1E | 7.74 |
2013 | 80.2N | 72.5W | 80.2S | 107.5E | 85.9N | 148.0W | 64.4S | 137.0E | 7.73 |
2014 | 80.2N | 72.5W | 80.2S | 107.5E | 85.9N | 149.0W | 64.3S | 136.8E | 7.73 |
2015 | 80.3N | 72.6W | 80.3S | 107.4E | 86.1N | 153.0W | 64.3S | 136.7E | 7.72 |
Table 1
Locations of magnetic poles and geomagnetic poles and
strength of dipole moment based on IGRF
(including prediction for after 2010).
Note that the actual magnetic poles must be
moving always by the effect of external currents
flowing in the ionosphere and magnetosphere,
and the change of the location could be about 80 km or more.
Please refer the pages in Geological
Survey of Canada for more detailed explanation.
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