5:15 PM - 7:15 PM
[SEM16-P18] Equatorial symmetry breaking of core convection during geomagnetic reversals in a geodynamo model
Keywords:numerical simulation, geomagnetic field, Earth’s core flow, planetary interior, magnetohydrodynamics (MHD), rotating shell
The Earth has a magnetic field with a dominant axial dipole component, aligned with the axis of rotation. Paleomagnetic measurements have shown that the geomagnetic field has reversed its polarity many times. The reversal mechanism has been investigated by several geodynamo simulations. Some of them have suggested that the equatorially antisymmetric flow during polarity reversals is stronger than that during stable periods, although convective motions in a rotating spherical shell are characterized by a dominant equatorially symmetric flow because of rotation.
In the present study, we focus on how the energy transfer occurs between equatorially symmetric and antisymmetric flow components. We perform MHD dynamo simulations in a rotating spherical shell, modeled by the Earth’s outer core, and evaluate the work done by buoyancy, inertia, and the Lorentz force for the equatorially symmetric and antisymmetric flows, averaged over the spherical shell. In general, the energy transfer to the equatorially antisymmetric flow is much smaller than that to the equatorially symmetric flow. However, as a polarity reversal approaches, we reveal that the energy transfer exhibits the following changes:
(i) Decrease in the transfer rate from the equatorially symmetric flow to the magnetic field
(ii) Increase in the transfer rate from the equatorially symmetric flow to the antisymmetric flow via advection
(iii) Following the increase in the advection, the energy injection into the equatorially antisymmetric flow by the buoyancy force increases
We also discuss characteristic differences between force balances during stable and reversal periods.
In the present study, we focus on how the energy transfer occurs between equatorially symmetric and antisymmetric flow components. We perform MHD dynamo simulations in a rotating spherical shell, modeled by the Earth’s outer core, and evaluate the work done by buoyancy, inertia, and the Lorentz force for the equatorially symmetric and antisymmetric flows, averaged over the spherical shell. In general, the energy transfer to the equatorially antisymmetric flow is much smaller than that to the equatorially symmetric flow. However, as a polarity reversal approaches, we reveal that the energy transfer exhibits the following changes:
(i) Decrease in the transfer rate from the equatorially symmetric flow to the magnetic field
(ii) Increase in the transfer rate from the equatorially symmetric flow to the antisymmetric flow via advection
(iii) Following the increase in the advection, the energy injection into the equatorially antisymmetric flow by the buoyancy force increases
We also discuss characteristic differences between force balances during stable and reversal periods.