Effect of subsurface radial differential rotation on flux-transport solar dynamos

A near-surface radial gradient of rotation was recently inferred and quantified from MDI f-modes observations by Corbard & Thompson (2001). We show, from our preliminary simulation of the large-scale solar magnetic field, by using a flux-transport type dynamo, that despite being strong, this gradient plays only a small role compared to the tachocline in shearing the poloidal fields to produce toroidal fields. This happens primarily because the turbulent diffusivity near the surface wins in the competition of generation versus decay of the magnetic fields unless an abnormally high α-effect is considered there. This supports the results of previous flux-transport as well as interface and overshoot layer dynamo models that the major toroidal fields of the Sun are generated in the tachocline.