Where is the solar dynamo?

Abstract

In this paper I review results from recent global magnetohydrodynamical numerical simulations of solar convection, as a springboard to address the question "Where is the solar dynamo". I first describe and contrast similarities and differences in the large-scale flows and magnetic fields such simulations can produce, with emphasis on polarity reversals (or lack thereof) in the large-scale magnetic components they generate. On the basis of these simulation results, I argue that some of the significant differences in the spatiotemporal evolution of the large-scale magnetic field can be traced to the competing effects of turbulent electromotive forces and induction by large-scale flows, whose mutual near-cancellation in the nonlinearly saturated regime leads to a high sensitivity to the numerical/physical treatment of small scales. Some of these recent simulation results also reopen the possibility that dynamo action driving the solar activity cycle may reside entirely within the convection zone, with the tachocline perhaps playing a lesser role than has been assumed in the last two decades. On the other hand, other subsets of simulations suggest that magnetohydrodynamical processes taking place within the tachocline may have a significant impact on timescales comparable to or longer than the primary cycle. © 2013 Published under licence by IOP Publishing Ltd.