This chapter is a short introduction to the use of models in atmospheric research and forecasting. In Section 8.1 we explain how a hierarchy of models – simple, intermediate and complex – can be used for gaining understanding of atmospheric behaviour and interpreting atmospheric data. In Section 8.2 we give brief details of the numerical methods used in the more complex theoretical models, while in Section 8.3 we outline the use of these models for forecasting and other purposes. In Section 8.4 we describe an example of a class of laboratory models of the atmosphere. Finally, in Section 8.5, we give some examples of atmospheric phenomena that arise from interactions between basic physical processes and that can be elucidated only with the aid of models of intermediate complexity.

The hierarchy of models

The basic philosophy of atmospheric modelling was outlined in Section 1.2. It was mentioned there that a hierarchy of models, from simple to complex, must be used for understanding and predicting atmospheric behaviour; this hierarchy is illustrated in Figure 8.1. The simple models (‘back-of-the-envelope’ or ‘toy’ models) involve a minimum number of physical components and are described by straightforward mathematical equations that can usually be solved analytically. These models provide basic physical intuition: most of the models considered earlier in this book are of this type. The intermediate models involve a small number of physical components but usually require a computer for solution of the mathematical equations.