Philosophy

An important aspect of scientific study is crystallised by the idea of a model. Having thought about a problem and gathered together all sorts of useful data, we begin to think we can see what is going on. In general the picture will be horrifyingly complicated, with many physical processes involved. For example, no model of large-scale atmospheric motion is likely ever to be able to reproduce the behaviour of individual cumulus clouds, but every model must include the vertical transport of heat, and possibly water vapour, by motion on that scale if it is to model properly the energy input to the free atmosphere.

Simulation

It may be that what we really want to do is to imitate the real world. This would be so if we wanted to sell our prediction to a user for example. We might then try to describe as many of the relevant processes as we could, usually in the form of equations, and using the best estimates of their parameters. This set could then be solved for appropriate initial conditions. Such a task would require the application of numerical methods and a large computer; hence the usual name of numerical model. When this simulation is executed using observed initial data, deficiencies become apparent.