The Sun's Polar Magnetic Field as a Key Constraint on Dynamo Models of the Solar Cycle

Abstract:

The strength of the sun's dipole moment at solar minimum is long known to be a good precursor for the forecasting of the amplitude of the following solar activity cycle. The buildup of the polar fields through the photospheric dispersal of magnetic flux liberated by the decay of active regions is now being modelled very accurately using a variety of surface flux transport models. Less clear is the role played by the polar fields in the dynamo loop. I some classes of dynamo models it is crucial, while in others it is a mere side-effect of the dynamo operating in the interior. In this presentation I will use a variety of current solar dynamo models to illustrate this diversity of roles played by the polar fields. I will also argue that at this point, the primary uncertainties lie not with the buildup of the polar fields, but rather with its submergence into the solar interior, the essential prerequisite for participating in the dynamo loop. Clarifying this key issue observationally requires an accurate accounting of magnetic flux balance for the polar caps (transport, emergence, submergence and in situ production) for which out-of-the-ecliptic observations are likely essential.