Repeated and Sudden Reversals of the Dipole Field Generated by a Spherical Dynamo Action
Jinghong Li,1*
Tetsuya Sato,12
Akira Kageyama12
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.
1 Department of Fusion Science, The Graduate
University for Advanced Studies, Toki, 509-5292, Japan.
2 Theory and Computer Simulation Center, National
Institute for Fusion Science, Toki, 509-5292, Japan.
*
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}tcsc.nifs.ac.jp
