Effect of realistic heat flux patterns on geodynamo simulations

• Heat flux heterogeneities atop the core perturb the dynamical state of the core. • An equatorial cooling that dominates polar cooling is destabilizing the dipole. • Reversals are obtained when westward zonal flows are disrupted. • The zonal antisymmetric energy ratio correlates with the dipole strength. • Rapid changes in the reversal frequency can be caused by true polar wander. The heat flux pattern at the core-mantle boundary (CMB) is known to affect the stability of the magnetic dipole in numerical simulations of the geodynamo. Variations in this pattern could explain the changes in the frequency of magnetic reversals through geological times. However, the exact relation between heat flux heterogeneities and the dynamo behaviour is still unclear. In this study, we explore the effect on numerical dynamo simulations of two heat flux patterns extracted from mantle models: one is representative of the present-day, and a second is dominated by a differential cooling between the equator and higher latitudes. Such a cooling contrast between the equatorial and polar regions, in isolation, has been shown to be key in controlling the propensity for dipole reversals. We apply these patterns on three dynamo simulations with varying magnetic field strength and zonal flow amplitudes, representing different potential dynamical states of the core. We find that the destabilization of the dipole occurs when the heat flux pattern disrupts the westward flows in the core, confirming earlier results obtained using idealized heat flux geometries. We also find the same link between the occurrence of reversals and the ratio of zonal antisymmetric magnetic to kinetic energy. More surprisingly, the dipole is destabilized when the heat flux pattern exerts even a slightly stronger cooling near the equator than in the polar regions, demonstrating the crucial role of latitudinal variations in the CMB heat flux.