Solar Physics:  The changing magnetic fields of the Sun are generated and maintained by a solar dynamo, the exact nature of which remains an unsolved fundamental problem in solar physics. K. Teweldebirhan, M. Miesch, and S. Gibson investigate the role and impact of converging flows toward Bipolar Magnetic Regions (BMR inflows) on the Sun’s global solar dynamo. These flows are large-scale physical phenomena that have been observed and so should be included in any comprehensive solar dynamo model. We have augmented the Surface flux Transport And Babcock–LEighton (STABLE) dynamo model to study the nonlinear feedback effect of BMR inflows with magnitudes varying with surface magnetic fields. This fully-3D realistic dynamo model produces the sunspot butterfly diagram and allows a study of the relative roles of dynamo saturation mechanisms such as tilt-angle quenching and BMR inflows. The results of our STABLE simulations show that magnetic field dependent BMR inflows significantly affect the evolution of the BMRs themselves and result in a reduced buildup of the global poloidal field due to local flux cancellation within the BMRs, to an extent that is sufficient to saturate the dynamo. As a consequence, for the first time, we have achieved fully 3D solar dynamo solutions in which BMR inflows alone regulate the amplitudes and periods of the magnetic cycles.

Cycling magnetic behavior

Cycling magnetic behavior for a solar dynamo saturated by bipolar-magnetic-region inflows. (a) Butterfly diagram of the longitudinally-averaged radial field ⟨Br ⟩ at the surface (r = R) as a function of latitude and time, highlighting fourteen magnetic cycles. Polar amplitudes can exceed 300 G but the color table saturates at ± 100G. (b) Diagram of longitudinally-averaged toroidal field 〈Bφ〉near the base of the convection zone (r = 0.72R). Red and blue denote eastward and westward field respectively. (c) ⟨Br ⟩ averaged over the north (blue) and south (red) polar regions, above latitudes of ± 70◦, plotted vs. time.Vertical dotted lines mark polar field reversals in the NH (blue) and SH (red). (d) is similar to (c) but for〈Bφ〉in the lower convection zone and averaged over the entire NH (blue) and SH (red), as opposed to just the polarregions as in (c), with a saturation level for the color table of 90 kG.