In a new paper published in Physics of the Earth and Planetary Interiors, I present the first self-consistent simulations performed at the physical conditions of Earth’s core of a stably stratified top layer in interplay with the underlying convection and dynamo action. I show that the interannual to decadal geomagnetic variations observed by geomagnetic satellites are largely incompatible with strong stratification and favour the hypothesis of a fully convective core.