Outstanding Issues in Solar Dynamo Theory

TL;DR

This paper reviews current understanding of the solar dynamo mechanism, highlights unresolved issues such as the alpha-effect and flux transport, and emphasizes the need for better constraints to develop reliable solar cycle models.

Contribution

It identifies key unresolved problems in solar dynamo theory and discusses how current observational and theoretical limitations hinder the development of a standard, predictive model.

Findings

Advances in magnetohydrodynamic dynamo theory improve understanding of the solar magnetic cycle.

Helioseismic observations help constrain some parameters in solar cycle models.

Significant uncertainties remain in processes like turbulent diffusion and flux pumping.

Abstract

The magnetic activity of the Sun, as manifested in the sunspot cycle, originates deep within its convection zone through a dynamo mechanism which involves non-trivial interactions between the plasma and magnetic field in the solar interior. Recent advances in magnetohydrodynamic dynamo theory have led us closer towards a better understanding of the physics of the solar magnetic cycle. In conjunction, helioseismic observations of large-scale flows in the solar interior has now made it possible to constrain some of the parameters used in models of the solar cycle. In the first part of this review, I briefly describe this current state of understanding of the solar cycle. In the second part, I highlight some of the outstanding issues in solar dynamo theory related to the the nature of the dynamo $\alpha$-effect, magnetic buoyancy and the origin of Maunder-like minima in activity. I also discuss how poor constraints on key physical processes such as turbulent diffusion, meridional circulation and turbulent flux pumping confuse the relative roles of these vis-a-vis magnetic flux transport. I argue that unless some of these issues are addressed, no model of the solar cycle can claim to be ``the standard model'', nor can any predictions from such models be trusted; in other words, we are still not there yet.