Bi-stable dipole polarity in spherical shell dynamo with quadruple convection

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.