Impact of Anomalous Active Regions on the Large-scale Magnetic Field of the Sun

Abstract

One of the major sources of perturbation in the solar cycle amplitude is believed to be the emergence of anomalous active regions that do not obey Hale’s polarity law and Joy’s law of tilt angles. Anomalous regions containing high magnetic flux that disproportionately impact the polar field are sometimes referred to as “rogue regions.” In this study, utilizing a surface flux transport model, we analyze the large-scale dipole moment buildup due to the emergence of anomalous active regions on the solar surface. Although these active regions comprise a small fraction of the total sunspot number, they can substantially influence the magnetic dipole moment buildup and subsequent solar cycle amplitude. Our numerical simulations demonstrate that the impact of “anti-Joy” regions on the solar cycle is similar to those of “anti-Hale” regions. We also find that the emergence time, emergence latitude, relative number, and flux distribution of anomalous regions influence the large-scale magnetic field dynamics in diverse ways. We establish that the results of our numerical study are consistent with the algebraic (analytic) approach to explaining the Sun’s dipole moment evolution. Our results are relevant for understanding how anomalous active regions modulate the Sun’s large-scale dipole moment buildup and its reversal timing within the framework of the Babcock–Leighton dynamo mechanism—now believed to be the primary source of solar cycle variations.