Alleviating alpha quenching by solar wind and meridional flow

TL;DR

This study investigates how solar wind and meridional flow can help reduce alpha quenching in solar dynamo models, showing that these mechanisms can sustain finite magnetic fields but often below equipartition levels.

Contribution

It demonstrates that magnetic helicity expulsion via solar wind and meridional flow can mitigate catastrophic alpha quenching in mean field dynamo models, providing insights into solar magnetic field saturation.

Findings

Solar wind alone can prevent catastrophic quenching.

Meridional circulation can reinforce helicity expulsion.

Saturated magnetic fields are below equipartition strength.

Abstract

We study the ability of magnetic helicity expulsion to alleviate catastrophic $\alpha$-quenching in mean field dynamos in two--dimensional spherical wedge domains. Motivated by the physical state of the outer regions of the Sun, we consider $\alpha^2\Omega$ mean field models with a dynamical $\alpha$ quenching. We include two mechanisms which have the potential to facilitate helicity expulsion, namely advection by a mean flow ("solar wind") and meridional circulation. We find that a wind alone can prevent catastrophic quenching, with the field saturating at finite amplitude. In certain parameter ranges, the presence of a large-scale meridional circulation can reinforce this alleviation. However, the saturated field strengths are typically below the equipartition field strength. We discuss possible mechanisms that might increase the saturated field.