Generation of a strong magnetic field using uniform heat flux at the surface of the core

The Earth's main magnetic field is thought to be generated by motions in the planet's fluid outer core, which lead to an effect similar to that of a dynamo. Recent high-resolution numerical simulations produce only a non-dipolar or a dipolar but comparatively weak magnetic field unlike that of the Earth. Older models that did generate a strong, Earth-like field needed to use unrealistically high viscosities for the core fluid. Common to most of the models is the assumption of a laterally uniform core-surface temperature. Here we use a low-viscosity geodynamo model to evaluate the effect of a different and more realistic boundary condition-a uniform heat flux at the surface of the core-on the simulation of an Earth-like magnetic field. Our results show that when the surface temperature is laterally uniform, only a weak magnetic field is generated because planetary-scale fluid circulations are suppressed. In contrast, a laterally uniform heat flux at the core's surface leads to large-scale convective flows, and a comparatively strong dipole-type magnetic field. Contrary to previous work, we suggest that thermal conditions at the core surface have a strong effect on low-viscosity geodynamo models.