The origin and effect of hemispheric helicity imbalance in solar dynamo

TL;DR

This study investigates how hemispheric magnetic helicity imbalance influences the symmetry breaking in solar magnetic fields using an axisymmetric dynamo model that includes nonlinear magnetic helicity conservation effects.

Contribution

It demonstrates the relationship between magnetic helicity imbalance and magnetic field parity, highlighting the role of fluctuations and fluxes in symmetry breaking.

Findings

Magnetic helicity imbalance follows the evolution of magnetic field parity.

Fluctuations can invert the causal relationship between helicity imbalance and parity.

Small-scale helicity evolution lags behind large-scale helicity due to flux differences.

Abstract

In this paper we study the effects of hemispheric imbalance of magnetic helicity density on breaking the equatorial reflection symmetry of the dynamo generated large-scale magnetic field. Our study employs the axisymmetric dynamo model which takes into account the nonlinear effect of magnetic helicity conservation. We find that the evolution of the net magnetic helicity density, in other words, the magnetic helicity imbalance, on the surface follows the evolution of the parity of the large-scale magnetic field. Random fluctuations of the $\alpha$-effect and the helicity fluxes can inverse the causal relationship, i.e., the magnetic helicity imbalance or the imbalance of magnetic helicity fluxes can drive the magnetic parity breaking. We also found that evolution of the net magnetic helicity of the small-scale fields follows the evolution of the net magnetic helicity of the large-scale fields with some time lag. We interpret this as an effect of the difference of the magnetic helicity fluxes out of the Sun from the large and small scales.