The origin of the helicity hemispheric sign rule reversals in the mean-field solar-type dynamo

TL;DR

This paper investigates the reversals of magnetic helicity sign in the Sun using a mean-field dynamo model, linking these reversals to dynamo wave propagation and boundary conditions, and proposing helicity as a dynamo tracer.

Contribution

It demonstrates how magnetic helicity reversals are connected to dynamo wave dynamics and boundary conditions, providing new insights into solar magnetic field evolution.

Findings

Magnetic helicity sign reversals follow the dynamo wave inside the convection zone.

Surface helicity patterns are influenced by boundary conditions at the convection zone top.

Fluctuations in dynamo parameters affect helicity reversal behavior.

Abstract

Observations of proxies of the magnetic helicity in the Sun over the past two solar cycles revealed reversals of the helicity hemispheric sign rule (negative in the North and positive in the South hemispheres). We apply the mean-field solar dynamo model to study the reversals of the magnetic helicity sign for the dynamo operating in the bulk of the solar convection zone. The evolution of the magnetic helicity is governed by the conservation law. We found that the reversal of the sign of the small-scale magnetic helicity follows the dynamo wave propagating inside the convection zone. Therefore, the spatial patterns of the magnetic helicity reversals reflect the processes which contribute to generation and evolution of the large-scale magnetic fields. At the surface the patterns of the helicity sign reversals are determined by the magnetic helicity boundary conditions at the top of the convection zone. We demonstrate the impact of fluctuations in the dynamo parameters and variability in dynamo cycle amplitude on the reversals of the magnetic helicity sign rule. The obtained results suggest that the magnetic helicity of the large-scale axisymmetric field can be treated as an additional observational tracer for the solar dynamo.