Solar dynamo

Summary

The solar dynamo is the process that generates the magnetic field of the Sun from the motions of its plasma. It is a case of dynamo theory. Differential rotation stretches a north–south poloidal field into an east–west toroidal field. Twisting motions or the decay of active regions turn the toroidal field back into a poloidal field of reversed sign. The cycle of these two steps produces the 11-year sunspot cycle and the 22-year magnetic cycle of the Sun. Mean-field models describe it by the induction equation for the averaged field, with an $\alpha$-effect and a turbulent diffusivity.