Scientists Link Earth’s Westward Drift of Magnetic Field and Superrotation of Inner Core

September 17, 2013

Science

Scientists Solved Riddle about Which Direction the Center of the Earth Spins

In a newly published study, researchers from the University of Leeds detail how they solved a 300-year-old riddle about which direction the center of the Earth spins, linking the observed westward drift of the magnetic field and superrotation of the inner core.

Scientists at the University of Leeds have solved a 300-year-old riddle about which direction the center of the Earth spins.

The Earth’s inner core, made up of solid iron, ‘superrotates’ in an eastward direction – meaning it spins faster than the rest of the planet – while the outer core, comprising mainly molten iron, spins westwards at a slower pace.

Although Edmund Halley – who also discovered the famous comet – showed the westward-drifting motion of the Earth’s geomagnetic field in 1692, it is the first time that scientists have been able to link the way the inner core spins to the behavior of the outer core. The planet behaves in this way because it is responding to the Earth’s geomagnetic field.

The findings, published in Proceedings of the National Academy of Sciences, help scientists to interpret the dynamics of the core of the Earth, the source of our planet’s magnetic field.

In the last few decades, seismometers measuring earthquakes traveling through the Earth’s core have identified an eastwards, or superrotation of the solid inner core, relative to Earth’s surface.

“The link is simply explained in terms of equal and opposite action”, explains Dr Philip Livermore, of the School of Earth and Environment at the University of Leeds. “The magnetic field pushes eastwards on the inner core, causing it to spin faster than the Earth, but it also pushes in the opposite direction in the liquid outer core, which creates a westward motion.”

The solid iron inner core is about the size of the Moon. It is surrounded by the liquid outer core, an iron alloy, whose convection-driven movement generates the geomagnetic field.

The fact that the Earth’s internal magnetic field changes slowly, over a timescale of decades, means that the electromagnetic force responsible for pushing the inner and outer cores will itself change over time. This may explain fluctuations in the predominantly eastwards rotation of the inner core, a phenomenon reported for the last 50 years by Tkalčić et al. in a recent study published in Nature Geoscience.

Other previous research based on archeological artifacts and rocks, with ages of hundreds to thousands of years, suggests that the drift direction has not always been westwards: some periods of eastwards motion may have occurred in the last 3,000 years. Viewed within the conclusions of the new model, this suggests that the inner core may have undergone a westwards rotation in such periods.

The authors used a model of the Earth’s core which was run on the giant super-computer Monte Rosa, part of the Swiss National Supercomputing Center in Lugano, Switzerland. Using a new method, they were able to simulate the Earth’s core with an accuracy about 100 times better than other models.

The study was a collaboration between the University of Leeds and the Swiss Federal Institute of Technology, Zurich.

Publication: Philip W. Livermore, et al., “Electromagnetically driven westward drift and inner-core superrotation in Earth’s core,” PNAS, 2013; doi: 10.1073/pnas.1307825110

Source: University of Leeds

Image: Earth cross section showing its internal structure from Shutterstock

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2 Responses to “Scientists Link Earth’s Westward Drift of Magnetic Field and Superrotation of Inner Core”

  1. Rick Says:

    This is awesome news and should reinforce the “big motor” theory!!

    Reply

  2. Conrad Winkelman Says:

    The article is claiming something that almost certainly is factually incorrect:

    “The Earth’s inner core, made up of solid iron, ‘superrotates’ in an eastward direction – meaning it spins faster than the rest of the planet – while the outer core, comprising mainly molten iron, spins westwards at a slower pace”.

    1 The Earth’s surface is rotation eastwards, in absolute terms relative to the Sun, at 1 RPD (1 Revolution per Day). . .this is why we see the Sun move westward relative to the Earth’s surface;

    2 The superrotation of the solid core means that it rotates eastward at (1+x) RPD relative. Here x is the amount of extra rotation relative to the Earth’s surface;

    3 If, as stated, the outer liquid core moves actually westwards then this means that this liquid core layer is moving westward relative to the Earth’s surface by amount y so that its rotation relative to the Sun is -(1+y) RPD

    4 It follows then that the rotation speed difference between the solid core and the liquid core is (2+x+y) RPD.

    I would claim that this is incorrect.
    If it were true at this moment in time then I claim that the such a terrific difference in speed would have at two mayor effects that are not happening:

    5 The magnetic field of the Earth would be orders of magnitude stronger than it is now. . it is extremely weak;
    6 The great shear forces that would exist between the solid core’s surface and the liquid core, due to the viscosity of the liquid iron alloy, AND the shear force between the solid outer rocky mantle and the liquid core would crate so much heat that in fact the core would start to melt and the liquid iron alloy would tend to become a gas. This great heating rate would melt the surface of the Earth in a relatively sort time. . .A model of the Earth that remains stable AS IT IS can not support such a counter rotation claim as the article suggests.

    Surely, what is meant instead is that the liquid iron alloy mantle surrounding the solid core is experiencing a WESTWARD RETARDATION FORCE from the magnetic field, so that it rotates eastwards slower by amount x that the solid core.

    That is the only thing that appears to makes sense.

    I am sure the Scientists that discovered the essential contents of the article have not written this article. . .some person that wrote this has made an error and the in the review process the error was missed.

    This sort of thing happens a lot and is responsible for many Science Myths that are in vogue by the general public.

    PS
    1 If the rotation difference were indeed as large as is suggested then the energy conversion into heat would decrease the speed differences rapidly, and this would mean that the past the speed difference would have been much greater yet.

    2 As a result if the great speed difference between core and liquid I would expect the liquid layer to be turbulent and this would create rapid fluctuations in the Earth’s magnetic field. This would only not be the case if the fluid shear occurs under laminar flow conditions, and thus would be so if the liquid iron alloy has a rather high viscosity. . .On this I have no direct conclusions to make but an extremely high viscosity would imply an extremely high magnetic retardation force.
    Measurements and calculations that have been made for this phenomenon will show, I predict, that the liquid mantle around the core rotates eastwards only slightly slower than the core does.

    Reply

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