Sensitivity of a Babcock-Leighton Flux-Transport Dynamo to Magnetic Diffusivity Profiles

Abstract

We study the influence of various magnetic diffusivity profiles on the evolution of the poloidal and toroidal magnetic fields in a kinematic flux transport dynamo model for the Sun. The diffusivity is a poorly understood ingredient in solar dynamo models. We mathematically construct various theoretical profiles of the depth-dependent diffusivity, based on constraints from mixing length theory and turbulence, and on comparisons of poloidal field evolution on the Sun with that from the flux-transport dynamo model. We then study the effect of each diffusivity profile in the cyclic evolution of the magnetic fields in the Sun, by solving the mean-field dynamo equations. We investigate effects on the solar cycle periods, the maximum tachocline field strengths, and the evolution of the toroidal and poloidal field structures inside the convection zone, due to different diffusivity profiles. We conduct three experiments: (I) comparing very different magnetic diffusivity profiles; (II) comparing different locations of diffusivity gradient near the tachocline for the optimal profile; and (III) comparing different slopes of diffusivity gradient for an optimal profile. Based on these simulations, we discuss which aspects of depth-dependent diffusivity profiles may be most relevant for magnetic flux evolution in the Sun, and how certain observations could help improve knowledge of this dynamo ingredient.