Abstract
Dynamo models relying on the Babcock-Leighton mechanism are successful in reproducing most of the solar magnetic field dynamical characteristics. However, considering that such models operate only above a lower magnetic field threshold, they do not provide an appropriate magnetic field regeneration process characterizing a self-sustainable dynamo. In this work we consider the existence of an additional α-effect to the Babcock-Leighton scenario in a mean-field axisymmetric kinematic numerical model. Both poloidal field regeneration mechanisms are treated with two different strength-limiting factors. Apart from the solar antisymmetric parity behavior, the main solar features are reproduced: cyclic polarity reversals, mid-latitudinal equatorward migration of strong toroidal field, poleward migration of polar surface radial fields, and the quadrature phase shift between both. Long-term variability of the solutions exhibits lenghty periods of minimum activity followed by posterior recovery, akin to the observed Maunder Minimum. Based on the analysis of the residual activity during periods of minimum activity, we suggest that these are caused by a predominance of the α-effect over the Babcock-Leighton mechanism in regenerating the poloidal field.
Highlights
The Sun is a magnetic active star, which undergoes periods of high and low magnetic activity approximately each 11 years
It is important to mention that the alignment with the equatorial direction is not perfect: sunspot pairs often display a systematic tilt, the leading spot being nearer the equator than the following one ‒ Joy’s law
As the activity cycle is initiated, sunspot appearance migrates towards the equatorial region, and after the end of the 11 years cycle they begin again to appear at approximately 30° latitude, but with an opposite polarity configuration
Summary
The Sun is a magnetic active star, which undergoes periods of high and low magnetic activity approximately each 11 years. In this case the poloidal and toroidal fields regeneration processes are spatially separated (recall Figure 1h to Figure 1j); means of transportation of the new polar surface magnetic flux generated by the Babcock-Leighton mechanism to the bottom of the convection zone is necessary.
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