Does nonaxisymmetric dynamo operate in the Sun?

TL;DR

This study investigates whether non-axisymmetric dynamo processes, influenced by stochastic perturbations and bipolar region decay, can explain the observed non-axisymmetric magnetic fields and activity variations on the Sun.

Contribution

It demonstrates that stochastic alpha-effect fluctuations and bipolar region decay can sustain non-axisymmetric solar magnetic fields within a mean-field dynamo framework.

Findings

Diffusive decay of bipolar regions is a primary source of non-axisymmetric fields.

Stochastic alpha-effect can produce super-cycle and deep activity decline periods.

Model aligns with four solar activity cycles and offers insights into stellar magnetic activity.

Abstract

We explore effects of random non-axisymmetric perturbations of kinetic helicity (the $\alpha$ effect) and diffusive decay of bipolar magnetic regions on generation and evolution of large-scale non-axisymmetric magnetic fields on the Sun. Using a reduced 2D nonlinear mean-field dynamo model and assuming that bipolar regions emerge due to magnetic buoyancy in situ of the large-scale dynamo action, we show that fluctuations of the $\alpha$ effect can maintain the non-axisymmetric magnetic fields through a solar-type $\alpha^{2}\Omega$ dynamo process. It is found that diffusive decay of bipolar active regions is likely to be the primary source of the non-axisymmetric magnetic fields observed on the Sun. Our results show that the non-axisymmetric dynamo model with stochastic perturbations of the $\alpha$ effect can explain periods of extremely high activity (`super-cycle' events) as well as periods of deep decline of magnetic activity. We compare the models with synoptic observations of solar magnetic fields for the last four activity cycles, and discuss implications of our results for interpretation of observations of stellar magnetic activity.