Vertically, the atmosphere was sliced into five layers. He divided the European area covered by the model into a lattice of 25 boxes, each about 200 kilometers on a side.
To apply his numerical techniques, Richardson had to replace the continuous space and time of the differential equations with discrete finite-difference equations. (They have since become a major industry.) It's worth noting that Richardson already had experience with such numerical methods, which were not then popular in the mathematics community. Finding an exact or analytic solution of these equations was not feasible, and so Richardson sought a numerical approximation. The inner mechanism of the mathematical model was a set of differential equations, relating quantities such as the instantaneous rate of change in air pressure to the horizontal and vertical components of the wind. His aim was to calculate the barometric pressure and the wind three hours later for two points near the middle of the continent. His initial data were observations made across Europe at 7 a.m. The focus is on the problematic forecast.īecause Richardson's pencil-and-paper arithmetic could not possibly keep pace with the evolution of the weather itself, his "prediction" actually concerned events long past. In The Emergence of Numerical Weather Prediction, Lynch gives a précis of the biographical background, but this book is not a general account of Richardson's life or even an overall assessment of his contributions to meteorology. A major biography by Oliver Ashford appeared in 1985, followed in 1993 by two volumes of collected papers. Richardson has gotten considerable attention in recent decades, not only for his work as a meteorologist but also for his later mathematical investigations of the causes of war and peace. "My office," he reported, "was a heap of hay in a cold rest billet." He performed his calculations between calls to carry wounded from the front. Richardson, a pacifist, was serving as a volunteer with the Friends Ambulance Unit in the north of France. Furthermore, the circumstances in which he did all this arithmetic have made the project legendary. Richardson, however, worked entirely with pencil and paper, using a sheaf of forms he had printed up to guide the computations his only aids to calculation were a slide rule and a table of logarithms.
Models based on essentially the same principles now run on supercomputers capable of trillions of operations per second. Richardson filled in initial values of pressure, wind velocity and so on, and then traced the model's evolution over time. For example, one rule says that if regions differ in barometric pressure, then air will start to flow along the gradient toward the lower-pressure area. He built a working mathematical model of the Earth's atmosphere, based on straightforward physical rules. Richardson's approach was more direct: He set out to calculate the weather. Then they'd look for earlier occasions when similar patterns occurred and try to make inferences about future developments from what happened in the past. Meteorologists would gather reports of current conditions and draw up charts showing geographic patterns of barometric pressure, wind, temperature and other variables. In Richardson's era, weather prediction was based mainly on a historical or analogical scheme.
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