Dynamics Of Earth's
Core Reveal Hurricanes
Under Your Feet
By Robert Roy Britt
Senior Science Writer

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.
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?
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.
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.
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:
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.
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.