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TOPIC: Earth’s magnetic field

Earth’s magnetic field 04 Feb 2015 08:32 #1

  • zax
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Earth’s magnetic field could flip within our lifetime – but don’t worry, we should be OK

This summer, the European Space Agency published data that suggested that the Earth’s magnetic field could flip — as in, the magnetic north pole becomes the magnetic south pole — in “a few thousand years.” At the time, I figured there was no rush to write it up — after all, we might not even be living on Earth in a few thousand years. Now, however, new research published this week shows that the magnetic field might flip within our lifetime — so it’s probably something that we ought to talk about.
As you probably remember from high school, the Earth is a giant bar magnet — a magnetic dipole with the north pole in the north, and the south pole in the south. If you imagine that there’s really a massive bar magnet in the middle of the Earth, it’s tilted by about 10 degrees from the planet’s axis, which is why the magnetic north pole — currently in the upper northern tracts of Canada — is a few hundred miles away from geographic/true north.

For now, magnetic north is close enough to true north that it doesn’t really matter (unless you’re trying to navigate using a compass in arctic or antarctic regions, in which case you’re in trouble). But the Earth’s magnetic field is shifting. New satellite data from the ESA shows that the Earth’s magnetic field is weakening 10 times faster than we previously thought — an indicator that scientists believe is a precursor to a geomagnetic reversal. At the time, there was nothing to worry about — previous geological records suggested that a geomagnetic reversal occurs over thousands of years. Now, however, a new study has analyzed rocks from the previous flip — the Matuyama-Brunhes magnetic reversal of 786,000 years ago — and found that the process completed in under 100 years. [doi: 10.1093/gji/ggu287]
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Earth’s magnetic field 22 Feb 2015 08:12 #2

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Magnetic Field of the Earth
Earth is surronded by a magnetic field. This magnetic field is similar to a dipole field generated by a bar magnet with a north and a south pole. The field lines converge (point vertically downward) at the north magnetic pole and emanate (point vertically upward) from the south magnetic pole. The imaginary bar magnet has an axis with a tilt of about 11 degrees compared to earth's axis of rotation and is offset from Earth's centre by about 550 kilometers.

In reality the shape of the geomagnetic field is more complex than a bar magnet. The field is not completely dipolar and it changes (its rate of change changes as well) with both location and time. Therefore the magnetic poles are not located in the same place as the north and south geographic poles of the earth. The generation of such a magnetic field is explained by a dynamo process due to the movement of the fluid (molten iron) outer core of the earth. Occasionally there is a magnetic field reversal where the field switches polarity. In this video, Lisa Tauxe from the Scripps Institution of Oceanography discusses the nature and origin of the earth's magnetic field, measuring and mapping its strength, and tracking its variations.

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