## Jule Charney, Agnar Fjörtoff & John von Neumann Report the First Weather Forecast by Electronic Computer 1950

In 1950 meteorologist Jule Charney of MIT, Agnar Fjörtoff, and mathematician John von Neumann of Princeton published “Numerical Integration of the Barotropic Vorticity Equation,” *Tellus* 2 (1950) 237-254. The paper reported the first weather forecast by electronic computer. It took twenty-four hours of processing time on the ENIAC to calculate a twenty-four hour forecast.

"As a committed opponent of Communism and a key member of the WWII-era national security establishment, von Neumann hoped that weather modeling might lead to weather control, which might be used as a weapon of war. Soviet harvests, for example, might be ruined by a US-induced drought.

"Under grants from the Weather Bureau, the Navy, and the Air Force, he assembled a group of theoretical meteorologists at Princeton's Institute for Advanced Study (IAS). If regional weather prediction proved feasible, von Neumann planned to move on to the extremely ambitious problem of simulating the entire atmosphere. This, in turn, would allow the modeling of climate. Jule Charney, an energetic and visionary meteorologist who had worked with Carl-Gustaf Rossby at the University of Chicago and with Arnt Eliassen at the University of Oslo, was invited to head the new Meteorology Group.

"The Meteorology Project ran its first computerized weather forecast on the ENIAC in 1950. The group's model, like [Lewis Fry] Richardson's, divided the atmosphere into a set of grid cells and employed finite difference methods to solve differential equations numerically. The 1950 forecasts, covering North America, used a two-dimensional grid with 270 points about 700 km apart. The time step was three hours. Results, while far from perfect, justified further work" (Paul N. Edwards [ed], *Atmospheric General Circulation Modeling: A Participatory History, *accessed 04-26-2009).

As Charney, Fjörtoff, and von Neumann reported:

"It may be of interest to remark that the computation time for a 24-hour forecast was about 24 hours, that is, we were just able to keep pace with the weather. However, much of this time was consumed by manual and I.B.M. oeprations, namely by the reading, printing, reproducing, sorting and interfiling of punch cards. In the course of the four 24 hour forecasts about 100,000 standard I.B.M. punch cards were produced and 1,000,000 multiplications and divisions were performed. (These figures double if one takes account of the preliminary experimentation that was carried out.) With a larger capacity and higher speed machine, such as is now being built at the Institute for Advanced Study, the non-arithmetical operations will be eliminated and the arithmetical operations performed more quickly. It is estimated that the total computation time with a grid of twice the Eniac-grids density, will be about 1/2 hour, so that one has reason to hope that RICHARDSON'S dream (1922) of advancing the computation faster than the weather may soon be realized, at least for a two-dimensional model. Actually we estimate on the basis of the experiences acquired in the course of the Eniac calculations, that if a renewed systematic effort with the Eniac were to be made, and with a thorough routinization of the operations, a 24-hour prediction could be made on the Eniac in as little as 12 hours." (pp. 274-75).