J. Jiang and R. H. Cameron

The ongoing 11-year cycle of solar activity is considerably less vigorous than the three cycles before. It was preceded by a very deep activity minimum with a low polar magnetic flux, the source of the toroidal field responsible for solar magnetic activity in the subsequent cycle. Simulation of the evolution of the solar surface field shows that the weak polar fields and thus the weakness of the present cycle 24 are mainly caused by a number of bigger bipolar regions with a ‘wrong’ (i.e., opposite to the majority for this cycle) orientation of their magnetic polarities in the North- South direction, which impaired the growth of the polar field. These reg ions had a particularly strong effect since they emerged within ±10° latitude from the solar equator.

R.H. Cameron

Hale’s polarity laws for sunspot groups, the helioseismic determination of differential rotation in the convection zone, and the success of surface flux transport models in reproducing the observed evolution of large-scale solar surface fields, together with a simple mathematical argument, yield compelling evidence that the large-scale solar dynamo operates according to the scenario originally envisaged by H.W. Babcock and R. Leighton in the 1960s. The polar fields represent THE poloidal flux from which the toroidal flux emerging in sunspot groups is wound up by (mainly latitudinal) differential rotation. The polar fields themselves result from tilted sunspot groups while small-scale magnetic features ("turbulence") do not provide a significant contribution.