PETTERSSEN, SVERRE

(b. Hadsel, Norway, 19 February 1898; d. London, United Kingdom, 31 December 1974), synoptic and dynamic meteorology, weather forecasting, aerology, wartime meteorology.

While theoretical meteorologists looked at Petterssen as a practical weather man, practitioners looked at him as a theoretician with some practical capability. But in reality he was both, which qualified him for important meteorological tasks during World War II, most notably the preparation of the weather forecast for the D-day landing 6 June 1944. Petterssen’s main achievement, however, was his teaching and a renowned textbook, which aimed at building a bridge between theory and practice in weather forecasting.

Education and Inspiration Petterssen was born to Edward H. Petterssen and Petronella Olava. He grew up in a fishing community in the Lofoten islands in north-ernmost Norway. Life was hard, opportunities meager, but challenging. As a young boy he followed the adult fishermen in open boats out to the fishing banks. He would have continued in his forefathers’ paths, had it not been for his gift and interest in the mathematical sciences.

In 1911 the family moved to Trondheim in central Norway, one of the major cities with its own university and high schools. His intellect earned him a scholarship to support his high school studies in physical sciences. To help him further economically in his education he attended an army school from 1915 to 1918 and earned the rank of sergeant before entering the University of Oslo.

In the summer of 1923 Petterssen, upon the advice of his geography professor, took part in a four-week international meteorological seminar in Bergen. It was organized by professor Vilhelm Bjerknes who had found that storms develop in the border zones (frontal zones) of major air masses of different densities. Now he was interested in attracting young talents to his meteorology group, which was working on guidelines that would help to predict storms more accurately.

Weather forecasting was a thankless job, mostly performed by poorly educated civil servants relying on experience, intuition, and luck. For Bjerknes and his collaborators it was a science in which methods could be taught, experience accumulated, and physically based causes and effects derived. The defining moment for Petterssen during the course came when one of the teachers, Tor Bergeron, introduced him to maps of a dramatic weather event, a rapid storm development in October 1921, which Vilhelm Bjerknes’s methods had managed to forecast. Bergeron’s discussion inspired Petterssen to become a meteorologist, to work on the problem of quantified weather predictions, and to explore the limits of predictability.

Work as a Weather Forecaster After a brief interlude as a forecaster in Oslo (1924–1926) where he took his BSc in 1924 and MSc in 1926, he moved to the Geophysical Institute in Tromsø in northernmost Norway. There he was instrumental in the successful forecast for the airship Norge crossing the North Pole from Spitsbergen to Alaska with the famous Danish explorer Roald Amundsen and the equally famous, but also adventurous, Italian explorer Umberto Nobile.

Two years later tragedy struck when Nobile, in a partly politically motivated expedition, reached the North Pole in an Italian-built airship, but did not follow Petterssen’s advice on the return trip, and ran into adverse weather. The highly publicized rescue efforts resulted in the death of Amundsen and others.

When the Tromsø bureau split into the Weather Forecasting Center for Northern Norway and the Northern Light observatory in 1928, Petterssen moved back to Bergen. There he replaced his old teacher Bergeron, who had begun some international engagements. In 1931 Petterssen was promoted to regional director for west Norway after Jacob Bjerknes.

The culture at Vilhelm Bjerknes’s weather service in Bergen encouraged cross-fertilization, to actively bridge the demarcation line between practical and academic meteorologists. The experiences the forecasters accumulated during a day’s shift were discussed from a scientific point of view; and new scientific ideas were examined to see if they could be included in the forecast routines.

Petterssen became the champion teacher with his ability to formulate working methods and principles that could be assimilated by other forecasters. Petterssen developed a series of simple mathematical expressions for the velocity, acceleration, and rate of development of weather fronts and pressure centers both at surface and upper levels. They did not necessarily increase the knowledge or understanding of atmospheric motion, but supplied the forecasters with workable tools to compute the movement and rate of development of storms. His work on the kinematics of the pressure field, summarized in his 1933 PhD thesis at Oslo University, was to see application in forecast offices in the coming years. As the amount and quality of observations from the atmosphere increased, it would become possible to make more extensive atmospheric maps, even in three dimensions.

Many prominent foreign meteorologists came to Bergen in the 1930s, several from the United States and Canada. In 1935 Sverre Petterssen was invited to spend almost a year in North America to give nationwide courses. When he returned in March 1936 he started to work on a professional textbook that would be published in 1940 with the title Weather Analysis and Forecasting, together with a more elementary Introduction to Meteorology (1941).

During a 1939 meeting in Berlin, where he was elected president of the Committee for Maritime Meteorology, he learned that Germany had educated 2,700 meteorologists, ten times more than the rest of Europe and the United States together, most of them with a doctoral degree.

Just before the war broke out Petterssen left Bergen and went to the Massachusetts Institute of Technology in Cambridge, where he replaced Carl-Gustaf Rossby as professor of meteorology. His warning about the mobilization of thousands of German meteorologists at first fell on deaf ears, until early in 1940 when thanks to Captain Arthur Merewether, the head of the U.S. Army Air Corps Weather Service, Petterssen was encouraged to start comprehensive weather courses. In 1941 he had 96 student forecasters, with 155 planned to come the following year. Pearl Harbor would accelerate this educational development but by then Petterssen had gone to the United Kingdom.

The War Years In August 1941 Petterssen was asked by the exiled Norwegian government in London to come to England to the Central Forecasting Office (CFO) located at the United Kingdom Meteorological Office in Dunstable, to help in the weather forecasting for the war effort. Petterssen, formally an officer in the Norwegian Air Force, but in effect a civilian, made secret arrangements for getting certain Norwegian meteorologists into England. Many eventually crossed over both from Norway and Sweden. Petterssen soon became a reinforcement to the team at the CFO and was a driving force in the initiation and elaboration of novel techniques of upper-air analysis and forecasting which were vital for the operations of the air forces.

Petterssen issued the forecast for the successful air attack against the German destroyer Tirpitz in 1942, which had sought shelter in a Norwegian fjord near Trondheim. Relying on his childhood acquaintance with the area and some scattered reconnaissance photos he was able to infer that a light breeze would develop and blow away Tirpitz’s fog cover and pave the way for a successful attack. An attempt by Norwegian commandos and British marines to destroy the German heavy-water facility near Vemork, Norway, in November 1942 failed disastrously because the group had ignored Petterssen’s warning about adverse weather.

The U.S. Army asked for his advice on vehicle traction in snow (he conducted field experiments on this) and the U.S. Navy on marine forecasting problems. In 1944 he was called to the Mediterranean to forecast for the successful invasion at the Anzio beachhead on April 22. In June the same year Petterssen was in the team of British and American meteorologists who successfully advised General Dwight D. Eisenhower on the D-day landing in Normandy.

A major bombing mission in the Balkans in early 1944 turned into a disaster because of unexpected strong upper winds. Petterssen taught pilots and meteorologists, mainly from theoretical viewpoints, to watch out for very strong upper-level winds above anticyclones of a specific internal thermal structure. When the war effort became more concentrated in the Pacific, Petterssen was sent there. During a course in Hawaii, he again warned about strong upper-level westerly winds of possibly 100 meters per second over Japan. He was not quite believed by the audience, some of whom would soon experience exactly this phenomenon on their air missions during winter 1945.

Administrator and Teacher During their occupation of Norway from 1940 to 1945, the Germans had established an effective telecommunication system for meteorology, a rather good network of radiosonde (weather balloon) stations and airport observation stations. When the war was over Petterssen returned to Norway to reorganize, direct, and expand the Norwegian Weather Service, in particular to meet the demands of aviation. The task offered lots of responsibilities and good pay but he was afraid that he would end up with too much administrative work.

After a short period as advisor to the Indian government early in 1948, he at first planned to accept a new chair in meteorology at Copenhagen University. This was abandoned when the Cold War convinced him to take up a renewed career in America, first as director of science services of the U.S. Air Force Weather Service in the period 1948–1952. From 1946 to 1951 Petterssen was president of the International Aerological Commission.

The arduous task of organization and administration did not leave as much time as he would have liked to study and write. His love for research and teaching again became too strong and he accepted an invitation in 1953 to become a professor at the University of Chicago, where he served as chair of the Department of Meteorology from 1959 to 1961, and then the Department of Geophysical Sciences until his retirement in 1963. He continued over the years to serve as an interim consultant to the U.S. armed services.

At the University of Chicago he founded a Weather Forecasting Research Center and set up a program to investigate the general question of storm development: its dynamics, energetics, and synoptic manifestations. In his later work he combined physical, dynamical, and kinematical principles with analysis of particular cases to obtain new results on the general circulation, propagation, and growth of jet-stream waves in relation to intensifications of cyclones. Inspired by similar work done by the British meteorologist R. C. Sutcliffe, Petterssen (1955) presented a development equation which in four terms expressed different dynamical-physical characteristics or processes crucial for the cyclone development.

Petterssen’s greatest fame rests with his major work Weather Analysis and Forecasting, a revised and updated version of his 1940 textbook expanded into two volumes. Issued in 1956, it is unique in its combination of basic science and technical application to give a coherent, although perhaps not complete, picture of meteorology and weather forecasting, presented in language and style of great clarity and almost artistic quality.

In hindsight it could be said that his textbook came too late. The work on computer-based forecasts had just started. Maturing into the postwar period of mathematical models and high-speed computers he might readily have entered this field; he was well qualified to do so, but characteristically he preferred to make his own approaches. As a part of the celebration of the Vilhelm Bjerknes centenary he presented an investigation of cyclone developments over the North Atlantic, inspired by the Bergen School (Petterssen et al., 1962). His work led ultimately (Petterssen and Smebye, 1971) to the recognition of two distinct types of extratropical cyclone development processes, one due to local influences, the other due to forcing from upstream influences. A planned investigation into the mechanism of indirect circulation, where sinking warm air and rising cold air, in discord with the schoolbook scenario, sharpens the thermal contrast during the intensification of cyclone, was never completed.

His Last Years Petterssen was president of the American Metrological Society (1958–1959) and in 1962 became a panelist member of President John F. Kennedy’s Scientific Advisory Committee for the atmospheric sciences. After his retirement he served as scientific attaché to the Scandinavian countries at the U.S. Embassy to Sweden in Stockholm from 1963 to 1965. Although he moved in October 1965 with his wife to live his last years in London, he still kept up his American connections and was up to 1971 an invited lecturer to several universities.

Numerous awards were bestowed on Petterssen: in 1948 the Buys Ballot Gold Medal and in 1951 the USAF Distinguished Service Award. In 1965 he was honored with the World Meteorological Organization Gold Medal and in 1969 with the Symons Gold Medal by the Royal Meteorological Society for “his outstanding contributions to the science of meteorology and weather forecasting” (Quarterly Journal of the Royal Meteorological Society, 1969).

Petterssen was a man of vitality, a lively philosopher, a bon vivant and a friendly humorous companion with an intriguing air of deep understanding and a neat turn of irony. He was “fun to be with.” Students looked forward to his classes because they were spiked with bons mots and other commentary on men and affairs. Petterssen said at the end of his life that he certainly had not got where he was by being methodical. He was not the type of scholar who pursues knowledge for its own sake. Knowledge had to have application, purpose, and fit into a scheme.

Maybe he felt like many other progressive meteorologists of his generation: they had much interest in the new ideas, but, at the same time, felt an undercurrent of regret.

With the arrival of the computer, days of the meteorological maestro were drawing to a close, along with a sort of subliminal fear that the fun was over and forecasting would never be the same again.

He was married three times. The first marriage, which was dissolved in 1939, resulted in two children, one son who moved to Boston and one daughter who remained in Norway. His second marriage was a short wartime marriage from September 1941 to October 1942 but the divorce was granted only in April 1947. By then Petterssen had already married his last wife, Grace, in June 1946.

Petterssen became a U.S. citizen in March 1955. During the Vietnam War and the Watergate scandal he gradually became alienated and disillusioned with the White House administration and in 1973 relinquished his U.S. citizenship, without reactivating his Norwegian citizenship. During his later years Petterssen suffered from heart problems after a heart attack in 1957. He died suddenly in London on 31 December 1974.

BIBLIOGRAPHY

WORKS BY PETTERSSEN

Weather Analysis and Forecasting: A Textbook on Synoptic Meteorology. New York: McGraw-Hill, 1940.

Introduction to Meteorology. New York: McGraw-Hill, 1941. 2^nd ed. 1958. 3^rd ed. 1969.

“A General Survey of Factors Influencing Development at Sea Level.” Journal of Meteorology 12 (1955): 36–42.

Weather Analysis and Forecasting. 2 vols. New York: McGraw-Hill, 1956. Revised and expanded edition of the 1940 textbook.

With D. L. Bradbury and K. Pedersen. “The Norwegian Cyclone Models in Relation to Heat and Cold Sources.” Geofysiske Publikasjoner 24 (1962): 243–280.

With S. J. Smebye. “On the Development of Extratropical Cyclones.” Quarterly Journal of the Royal Meteorological Society 97 (1971): 457–482.

Kuling fra nord: En værvarslers erindringer. [Gale from the north: a weather forecaster’s reminiscences]. Oslo: Aschehoug, 1974. Translated from the original English to Norwegian, he sums up the experiences and philosophy of an extremely active, exciting, and fruitful life. He told his friends that he originally intended to make the title Tales of a Maverick in Science, later to be changed to Of Storms and Men.

Weathering the Storm: Sverre Petterssen, the D-Day Forecast and the Rise of Modern Meteorolog y, edited by James R. Fleming. Boston: American Meteorological Society, 2001. The original English autobiography with added footnotes and a selected bibliography.

OTHER SOURCES

Bundgaard, R. C. “Sverre Petterssen, Weather Forecaster.” Bulletin of the American Meteorological Society 60, no. 3 (1979): 182–195. A summary of Petterssen’s 1974 autobiography.

Fleming, James R. “Sverre Petterssen, the Bergen School, and the Forecasts for D-Day.” History of Meteorology 1 (2004): 75–83. Available from http://www.meteohistory.org.

Johannessen, K. R. “Sverre Petterssen 1898–1974.” Bulletin of the American Meteorological Society 56, no. 8 (1975): 892–893.

Mason, B. J., and J. S. Sawyer. “Professor Sverre Petterssen.” Meteorological Magazine 104 (1975): 93–94.

Sutcliffe, R. C. “Professor Sverre Petterssen, C.B.E.” Quarterly Journal of the Royal Meteorological Society 101 (1975): 703–704.

Anders Persson