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In this paper we address a discrepancy between the surface flux evolution ina 3D kinematic dynamo model and a 2D surface flux transport model that has beenclosely calibrated to the real Sun. We demonstrate that the difference is dueto the connectivity of active regions to the toroidal field at the base of theconvection zone, which is not accounted for in the surface-only model.Initially, we consider the decay of a single active region, firstly in asimplified Cartesian 2D model and subsequently the full 3D model. By varyingthe turbulent diffusivity profile in the convection zone, we find thatincreasing the diffusivity - so that active regions are more rapidlydisconnected from the base of the convection zone - improves the evolution ofthe surface field. However, if we simulate a full solar cycle, we find that thedynamo is unable to sustain itself under such an enhanced diffusivity. Thissuggests that in order to accurately model the solar cycle, we must find analternative way to disconnect emerging active regions, whilst conservingmagnetic flux.

The need for active region disconnection in 3D kinematic dynamo simulations