Simulation Study of Hemispheric Phase-Asymmetry in the Solar Cycle

TL;DR

This study uses a flux transport dynamo model to theoretically explain the hemispheric phase-asymmetry observed in solar cycles, revealing two attractors that account for the asymmetry without additional assumptions.

Contribution

It demonstrates that the flux transport dynamo model can naturally produce hemispheric asymmetries through inherent attractors, without needing external asymmetry sources.

Findings

Identified two attractors corresponding to hemispheric phase reversals.

The model reproduces observed sunspot and polar field asymmetries.

Explains asymmetry as a natural outcome of the dynamo process.

Abstract

Observations of the sun suggest that solar activities systematically create north-south hemispheric asymmetries. For instance, the hemisphere in which the sunspot activity is more active tends to switch after the early half of each solar cycle. Svalgaard & Kamide (2013) recently pointed out that the time gaps of polar field reversal between the north and south hemispheres are simply consequences of the asymmetry of sunspot activity. However, the mechanism underlying the asymmetric feature in solar cycle activities is not yet well understood. In this paper, in order to explain the cause of the asymmetry from the theoretical point of view, we investigate the relationship between the dipole- and quadrupole-type components of the magnetic field in the solar cycle using the mean-field theory based on the flux transport dynamo model. As a result, we found that there are two different attractors of the solar cycle, in which either the north or the south polar field is first reversed, and that the flux transport dynamo model well explains the phase-asymmetry of sunspot activity and the polar field reversal without any ad hoc source of asymmetry.