TY - JOUR
T1 - A numerical study on magnetic polarity transition in an MHD dynamo model
AU - Takahashi, Futoshi
AU - Matsushima, Masaki
AU - Honkura, Yoshimori
N1 - Funding Information:
Acknowledgments. Numerical simulation was carried out on the Earth Simulator under the support of JAMSTEC. The authors are very grateful to Robert S. Coe and Johannes Wicht for their useful comments and constructive discussion, which substantially improved the manuscript. Futoshi Takahashi was supported by Research Fellowships of the Japan Society for the Promotion of Science for young scientists. This work is partially supported by the Japan Society for the Promotion of Science under the grant-in-aid for scientific research No. 18340131.
PY - 2007
Y1 - 2007
N2 - Magnetic polarity transitions in a Takahashi-Matsushima-Honkura dynamo model are analyzed. Distinctive differences in behavior of the axisymmetric poloidal magnetic field are found among a polarity reversal and excursions, including short polarity events. At the beginning of magnetic polarity transitions, the magnetic field with the reversed polarity is generated by anti-cyclonic convection columns deep within the outer core. In the case of excursion, it is soon advected by the radial flow toward a shallow interior of the core, and the transition can be detected at the core surface. However, the same process retrieves the original polarity from the deep interior, and the reversed field eventually vanishes. In the case of polarity reversal, on the other hand, the reversed polarity field is persistently generated deep within the core. It is then advected toward a shallow interior of the core, while the generation process of the reversed field occurs successively. The reversed polarity field near the core surface is collected by the downwelling flow associated with convection columns, as is the case for the original polarity field. The polarity reversal is completed by the advection process, the duration of which is consistent with the flow speed in the core.
AB - Magnetic polarity transitions in a Takahashi-Matsushima-Honkura dynamo model are analyzed. Distinctive differences in behavior of the axisymmetric poloidal magnetic field are found among a polarity reversal and excursions, including short polarity events. At the beginning of magnetic polarity transitions, the magnetic field with the reversed polarity is generated by anti-cyclonic convection columns deep within the outer core. In the case of excursion, it is soon advected by the radial flow toward a shallow interior of the core, and the transition can be detected at the core surface. However, the same process retrieves the original polarity from the deep interior, and the reversed field eventually vanishes. In the case of polarity reversal, on the other hand, the reversed polarity field is persistently generated deep within the core. It is then advected toward a shallow interior of the core, while the generation process of the reversed field occurs successively. The reversed polarity field near the core surface is collected by the downwelling flow associated with convection columns, as is the case for the original polarity field. The polarity reversal is completed by the advection process, the duration of which is consistent with the flow speed in the core.
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U2 - 10.1186/BF03352729
DO - 10.1186/BF03352729
M3 - Article
AN - SCOPUS:34547981109
VL - 59
SP - 665
EP - 673
JO - Earth, Planets and Space
JF - Earth, Planets and Space
SN - 1343-8832
IS - 7
ER -