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 plotting rotational characteristics of the Earth's molten core -- spinning works.
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.
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.
What's going on down there?
Though Earth's inner core is mostly solid iron, a more fluid, molten iron outer core surrounds it. The two regions rotate at different speeds and, it is believed, 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.
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 from 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.
Peter Olson, lead researcher on the new study, explained that Earth's outer core appears to rotate in the opposite direction of its inner core, generating conditions much like those that create atmospheric vortices, such as hurricanes:
Near the surface, a hurricane in the Northern Hemisphere rotates in a counterclockwise (cyclonic) direction. 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. Based on this atmospheric paradigm, he therefore expects that deeper in the core, circulation ought to change direction and become cyclonic.
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.
"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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