By Steve Graham, Claire Parkinson, and Mous Chahine
February 25, 2002

Imagine a rotating sphere that is 12,800 kilometers (8000 miles) in diameter, has a bumpy surface, is surrounded by a 40-kilometer-deep mixture of different gases whose concentrations vary both spatially and over time, and is heated, along with its surrounding gases, by a nuclear reactor 150 million kilometers (93 million miles) away. Imagine also that this sphere is revolving around the nuclear reactor and that some locations are heated more during one part of the revolution and other locations are heated during another part of the revolution. And imagine that this mixture of gases continually receives inputs from the surface below, generally calmly but sometimes through violent and highly localized injections. Then, imagine that after watching the gaseous mixture, you are expected to predict its state at one location on the sphere one, two, or more days into the future. This is essentially the task encountered day by day by a weather forecaster (Ryan, Bulletin of the American Meteorological Society,1982).

Earth rotates on its axis once every 23 hours, 56 minutes, and completes one revolution around the sun every 365.25 days. (Courtesy of Rob Simmon.)

Weather Forecasting Through the Ages
Introduction
Early History
Towards Numerical Prediction
Modern Tools of the Trade
The Aqua Spacecraft
Benefits to Society
References

next: Early History