Abstract
To study nonlinear dynamo properties, we performed extensive MHD simulations in a spherical shell system, focusing on a quadruple convection pattern with equal amounts of positive and negative flow helicities in the southern and northern hemispheres. Simulations using 50 different magnetic noise patterns indicate that the system settles into a nonlinear dipole-dominated equilibrium, with north or south polarity occurring at similar rates. This finding is consistent with the results from 50 additional simulations in which the direction of the convection is reversed. Both stable polarity states exhibit significant robustness, showing resistance to reversal under minor magnetic disturbances. This indicates that a bi-stable polarity equilibrium exists in the dipole-dominated magnetic field of a spherical shell dynamo system. The stable polarity state can be disrupted by introducing anomalous magnetic diffusivity or viscosity, or plasma instability, which are beyond the scope of this report.
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
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Acknowledgements
The authors are grateful to Prof. A. Kageyama (Kobe Univ.) for providing the numerical code and stimulating discussions and to Prof. Emeritus S. Ishiguro (NIFS) for stimulating discussions. Finally, the authors would like to announce that this work is the first product under the “Future-Telescope Project” that has been launched recently by the Simulation Group of NIFS and Japan Society of Simulation Technology.
Funding
This work is supported by the NINS program of Promoting Research by Networking among Institutions (Grant Number 01422301). Simulations were carried out on the “Plasma Simulator (PS)” (NEC SX-Aurora TSUBASA) of NIFS under the auspices of the NIFS Collaboration Research programs (NIFS24KISM005).
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H.H. and T.S. designed and conceived this study. H.H. developed the simulation code. H.H. and H.O. performed the simulations and the analysis. H.O. was involved in visualization of the simulation data. H.H. and T.S. drafted the manuscript and designed the figures. All authors discussed the results and commented on the manuscript.
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Hasegawa, H., Ohtani, H. & Sato, T. Bi-stable dipole polarity in spherical shell dynamo with quadruple convection. Sci Rep (2026). https://doi.org/10.1038/s41598-026-42280-x
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DOI: https://doi.org/10.1038/s41598-026-42280-x
