1.2 What is a “model”?
The review’s very title demands an explanation of what is to be understood by “model”. A model is a
theoretical construct used as thinking aid in the study of some physical system too complex to be
understood by direct inferences from observed data. A model is usually designed with some specific
scientific questions in mind, and asking different questions about a given physical system will, in all
legitimacy, lead to distinct model designs. A well-designed model should be as complex as it needs to be to
answer the questions having motivated its inception, but no more than that. Throwing everything into a
model – usually in the name of “physical realism” – is likely to produce results as complicated as the data
coming from the original physical system under study. Such model results are doubly damned, as they
are usually as opaque as the original physical data, and, in addition, are not even real-world
Nearly all of the solar dynamo models discussed in this review rely on severe simplifications of the set of
equations known to govern the dynamics of the Sun’s turbulent, magnetized fluid interior. Yet all of them
are bona fide models, as defined here.