3 Mechanisms of Magnetic Field Generation
The Sun’s poloidal magnetic component, as measured on photospheric magnetograms, flips polarity near
sunspot cycle maximum, which (presumably) corresponds to the epoch of peak internal toroidal field .
The poloidal component , in turn, peaks at time of sunspot minimum. The cyclic regeneration
of the Sun’s full large-scale field can thus be thought of as a temporal sequence of the form
where the and refer to the signs of the poloidal and toroidal components, as established
observationally. A full magnetic cycle then consists of two successive sunspot cycles. The dynamo problem
can thus be broken into two sub-problems: generating a toroidal field from a pre-existing poloidal
component, and a poloidal field from a pre-existing toroidal component. In the solar case, the former turns
out to be easy, but the latter is not.