Dynamo Theory

Abstract

At the photosphere the Sun’s magnetic field is concentrated into intense flux tubes and also into sunspots (Sections 1.3.2B, 1.4.2, and Chapter 8), whose detailed evolution is highly complex, but whose overall behaviour is remarkably ordered as the solar cycle proceeds (Section 1.4.2E). This underlying pattern shows up in several ways:

• 1 the 11-yr oscillation in sunspot number;

• 2 the restriction of sunspots to two belts of latitude;

• 3 the spread and drift towards the equator of the sunspot belts (Sporer’s Law);

• 4 the inclination of sunspot groups (by typically 10°) to the equator;

• 5 the laws of polarity (Figure 1.29);

• 6 the reversal of the polar fields near sunspot maximum.

All these features are commonly thought to be caused by some kind of dynamo mechanism operating in the largely unobservable depths of the convective zone, but the details of such an interaction between plasma and magnetic field are not yet fully understood. The problems are first of all to show that a magnetic field may, in act, be maintained and then to reproduce the above features of the solar cycle.