- Richardson's "Forecast Factory"
- Computers, Weather, and War in the 1940s
- The Swedish Institute of Meteorology
- The Joint Numerical Weather Prediction Unit
- References

In the early 20^{th} century, the
Norwegian Vilhelm Bjerknes argued that atmospheric physics had
advanced sufficiently to allow weather to be forecast using
calculations. He developed a set of seven equations whose solution
would, in principle, predict large-scale atmospheric motions.

Bjerknes proposed a "graphical calculus," based on weather maps, for
solving the equations. Although his methods continued to be used and
developed until the 1950s, both the lack of faster calculating
methods and the dearth of accurate observational data limited their
success as forecasting techniques.[1]

In 1922, Lewis Fry Richardson developed the
first numerical weather prediction (NWP) system. His calculating
techniques -- division of space into grid cells; finite difference
solutions of differential equations -- were the same ones employed by
the first generations of AGCM builders. Richardson's method, based on
simplified versions of Bjerknes's "primitive equations" of motion and
state (and adding an eighth variable, for atmospheric dust) reduced
the calculations required to a level where manual solution could be
contemplated. Still, this task remained so large that Richardson did
not imagine it as a weather forecast technique. His own attempt to
calculate weather for a single eight-hour period took six weeks and
ended in failure.

His model's enormous calculation requirements led Richardson to
propose a fanciful solution he called the "forecast-factory." The
"factory" -- really more like a vast orchestral performance --
would have filled a vast stadium with 64,000 people. Each one, armed
with a mechanical calculator, would perform part of the calculation.
A leader in the center, using colored signal lights and telegraph
communication, would coordinate the forecast.

Yet even with this fanciful apparatus, Richardson thought he would
probably be able to calculate weather only about as fast as it
actually happens. Only in the 1940s, when digital computers made
possible automatic calculation on an unprecedented scale, did
Richardson's technique become practical.[2]

The Princeton mathematician John von Neumann
was among the earliest computer pioneers. Engaged in computer
simulations of nuclear weapons explosions, he immediately saw
parallels to weather prediction. (Both are non-linear problems of
fluid dynamics.) In 1946, soon after the ENIAC became operational,
von Neumann began to advocate the application of computers to weather
prediction.[3]
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.[4]

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 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.[5]

The Royal Swedish Air Force Weather Service in Stockholm was first in the world to begin routine real-time numerical weather forecasting (i.e., with broadcast of forecasts in advance of weather). The Institute of Meteorology at the University of Stockholm, associated with the eminent meteorologist Carl-Gustaf Rossby, developed the model. Forecasts for the North Atlantic region were made three times a week on the Swedish BESK computer using a barotropic model, starting in December, 1954.[6]

About 1952, Von Neumann, Charney, and others
convinced the Weather Bureau and several research and forecasting
agencies of the Air Force and Navy to establish a Joint Numerical
Weather Prediction (JNWP) Unit. The JNWP Unit opened in Suitland,
Maryland in 1954, under George Cressman. It began routine real-time
weather forecasting in May, 1955.[7]
Yet it was well over a decade before numerical methods began to
outstrip in accuracy the "subjective method" employed by human
forecasters.

Initially, the computer models used for NWP employed simplifying
assumptions. Only in the 1960s did models based on the
Bjerknes/Richardson primitive equations replace barotropic and
baroclinic models.

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References

[1]
F. Nebeker, *Calculating the Weather: Meteorology in the 20th
Century* (New York: Academic Press, 1995).

[2]
L.F. Richardson, *Weather Prediction by Numerical Process*
(Cambridge: Cambridge University Press, 1922).

[3]
W. Aspray, *John von Neumann and the Origins of Modern
Computing* (Cambridge, MA: MIT Press, 1990).

[4]
C. Kwa, "The Rise and Fall of Weather Modification," in *Changing
the Atmosphere: Expert Knowledge and Global Environmental
Governance*, eds. C.A. Miller and P.N. Edwards and (Cambridge, MA:
MIT Press, forthcoming, 2000).

C. Kwa, "Modelling Technologies of Control," *Science as
Culture* 4, no. 20 (1994): 363-391.

[5]
J.G. Charney, R. Fjörtoft, and J.v. Neumann, "Numerical
integration of the barotropic vorticity equation," *Tellus* 2
(1950): 237-254.

G.W. Platzman, "The ENIAC computations of 1950 -- gateway to
numerical weather prediction," *Bulletin of the American
Meteorological Society* 60 (1979): 302-312.

[6]
Staff Members of the Institute of Meteorology, University of
Stockholm, "Results of Forecasting with the Barotropic Model on an
Electronic Computer (BESK)," *Tellus* 6 (1954): 139-149.

P. Bergthorsson et al., "Routine Forecasting with the Barotropic
Model," *Tellus* 7 (1955): 272-274.

[7]
F. Nebeker, *Calculating the Weather: Meteorology in the 20th
Century* (New York: Academic Press, 1995).

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