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 T. The poloidal component P, 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

P (+) → T (− ) → P(− ) → T (+ ) → P (+) → ..., (9 )
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.

 3.1 Poloidal to toroidal
 3.2 Toroidal to poloidal
  3.2.1 Turbulence and mean-field electrodynamics
  3.2.2 Hydrodynamical shear instabilities
  3.2.3 MHD instabilities
  3.2.4 The Babcock–Leighton mechanism

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