Repeated and Sudden Reversals of the Dipole Field Generated by a Spherical Dynamo Action

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Science  08 Mar 2002:
Vol. 295, Issue 5561, pp. 1887-1890
DOI: 10.1126/science.1066959

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Using long-duration, three-dimensional magnetohydrodynamic simulation, we found that the magnetic dipole field generated by a dynamo action in a rotating spherical shell repeatedly reverses its polarity at irregular intervals (that is, punctuated reversal). Although the total convection energy and magnetic energy alternate between a high-energy state and a low-energy state, the dipole polarity can reverse only at high-energy states where the north-south symmetry of the convection pattern is broken and the columnar vortex structure becomes vulnerable. Another attractive finding is that the quadrupole mode grows, exceeding the dipole mode before the reversal; this may help to explain how Earth's magnetic field reverses.

  • * Permanent address: Institute of Applied Physics and Computational Mathematics, Post Office Box 8009, Beijing 100088, China.

  • To whom correspondence should be addressed. E-mail: sato{at}

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