I'd say it's the ferrite on the surface that is magnetically charged and creates the magnetic fields to begin with. The iron ions are carried into the arc, and the electrical current within the arc creates it's own set of magnetic fields. When the magnetic poles point roughly toward the equator, it creates a condition where one side of the equator is more positively charged while the other side is being negatively charged. This creates an active condition where sunspots start to interact not only with the area around it, but with other sunspots in the other hemisphere as well. Things get VERY hot indeed!

When the magnetic poles align themselves with the spin axis, things are relatively "quiet" on the surface.