The Global Solar Dynamo

TL;DR

This paper reviews the observational constraints and theoretical models of the solar dynamo, focusing on the alpha-omega Babcock-Leighton type, and discusses open questions about subsurface dynamics and magnetic helicity fluxes.

Contribution

It provides a comprehensive overview of the current understanding and open questions in solar dynamo research, emphasizing the role of magnetic helicity fluxes and subsurface processes.

Findings

Sunspots emerge at preferred latitudes, forming butterfly wings.

The solar cycle lasts about 11 years.

Magnetic helicity fluxes influence large-scale magnetic field evolution.

Abstract

A brief summary of the various observations and constraints that underlie solar dynamo research are presented. The arguments that indicate that the solar dynamo is an alpha-omega dynamo of the Babcock-Leighton type are then shortly reviewed. The main open questions that remain are concerned with the subsurface dynamics, including why sunspots emerge at preferred latitudes as seen in the familiar butterfly wings, why the cycle is about 11 years long, and why the sunspot groups emerge tilted with respect to the equator (Joy's law). Next, we turn to magnetic helicity, whose conservation property has been identified with the decline of large-scale magnetic fields found in direct numerical simulations at large magnetic Reynolds numbers. However, magnetic helicity fluxes through the solar surface can alleviate this problem and connect theory with observations, as will be discussed.