78 Modelling theclimate
Figure 5.1Illustrating the growth of computer power available at major
forecasting centres. The computers are those used by the UK Meteorological
Office for numerical weather prediction research, since 1965 for operational
weather forecasting and most recently for research into climate prediction.
Richardson’s computer refers to his dream of a large ‘human’ computer
mentioned at the beginning of the chapter.so that the integration of the numerical model could keep up with the
weather. But he was many years before his time! It was not until some
forty years later that, essentially using Richardson’s methods, the first
operational weather forecast was produced on an electronic computer.
Computers more than one million times faster than the one used for that
first forecast (Figure 5.1) now run the numerical models that are the basis
of all weather forecasts.
Numerical models of the weather and the climate are based on the
fundamental mathematical equations that describe the physics and dy-
namics of themovements and processes taking place in the atmosphere,
the ocean, the ice and on the land. Although they include empirical
information, they are not based to any large degree on empirical rela-
tionships – unlike numerical models of many other systems, for instance
in the social sciences.
Setting up a model of the atmosphere for a weather forecast (see Fig-
ure 5.2) requires a mathematical description of the way in which energy
from the Sun enters the atmosphere from above, some being reflected
by the surface or by clouds and some being absorbed at the surface or
in the atmosphere (see Figure 2.6). The exchange of energy and water
vapour between the atmosphere and the surface must also be described.