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- You've got to hand it to nature: Once it finds something
that works, it sticks with it. Take vortices for example: from the nearly
incomprehensible rotation of galaxies to the familiar swirl of a hurricane
right down to plodding rotational characteristics of the Earth's molten
core, spinning works.
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- The nice thing about vortices in the atmosphere - tornadoes,
hurricanes and cyclones - is that you can see them. Complicated and violent
as these phenomena are, being able to see them makes it relatively easy
to study them -- compared, that is, with the vortices beneath your feet.
This could explain why researchers have only recently confirmed their existence.
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- In recent years scientists used computer models to predict
that there would be cyclonic systems in the fluid portion of Earth's core.
Now researchers at Johns Hopkins University say they've proved this theory.
In a paper appearing in Thursday's issue of the journal Nature, researchers
say they have confirmed the presence of a vortex in the Northern Hemisphere.
The scientists studied the earth's magnetic field, going as far back as
1870, to draw their conclusion.
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- What's going on down there?
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- Earth's inner core is mostly solid iron, surrounded by
a more fluid, molten iron outer core. The two regions rotate at different
speeds and not always in the same direction. This interaction creates what
scientists call a "hydromagnetic dynamo," something like an electric
motor that results in the magnetic field that surrounds our planet.
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- Researchers have known that convection -- the upward
motion of heated material -- is at the root of much of this activity. With
a hurricane, warm, rising air of a low-pressure system drives the storm.
In the Northern Hemisphere, the movement of air into a hurricane is deflected,
by the Earth's rotation, into a counterclockwise (cyclonic) motion. The
opposite rotation occurs in the Southern Hemisphere.
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- Peter Olson, lead researcher on the new study, explained
that the rotation of Earth's outer core is in the opposite direction compared
to the inner core, generating conditions much like those that create atmospheric
vortices like hurricanes:
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- Near the surface, a hurricane rotates in a counterclockwise
(cyclonic) fashion, but as air is pushed by convection to higher altitudes,
the motion becomes clockwise (anticyclonic). Olson says the same anticyclonic
circulation is seen near the top of the outer core. He therefore expects
that deeper in the core, circulation ought to change direction and become
cyclonic.
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- The study should help researchers better understand the
dynamics of inner Earth, which is the origin for the magnetic field that
guides compasses and protects our planet from harmful cosmic radiation.
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- "The magnetic field is carried by the vortex, and
in addition, we suppose that the field is (partly) generated by the vortex
deeper within the core," Olson said.
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