Rossby Carl Gustav 18981957

CARL-GUSTAV ROSSBY WAS a Swedish-American meteorologist whose innovations in the study of large-scale air movement and introduction of the equations describing atmospheric motion were largely responsible for the rapid development of meteorology as a science. Rossby explained the large-scale motions of the atmosphere in terms of fluid mechanics and was one of the first scientists to notice the problem of global warming.

Rossby was born on December 28, 1898, in Stockholm, Sweden. When he was 20, he moved to Bergen, Norway, to study under pioneering atmospheric scientist Vilhelm Bjerknes at the Geophysical Institute. At that time, Bjerknes and his so-called Bergen School were making great progress in laying the foundations of meteorology as a science with their breakthroughs in the polar front theory and air mass analysis. The center was the world's leading center of meteorological research. The young Rossby contributed his brilliant ideas to the development of the group's projects. Because of the impact of Bjerknes's guidance, Rossby, who had previously been interested in studying mathematics and astronomy, committed himself to meteorology.

Rossby moved to the United States in 1926, where he worked in Washington, D.C. He was employed as a fellow of the American-Scandinavian Foundation

Carl-Gustav Rossby with a rotating tank used to study atmospheric motion. Rossby explained atmospheric motion.

for Research at the U.S. Weather Bureau to explain the innovations of the polar front theory. While at the Weather Bureau Rossby established the first weather service for civil aviation. The Weather Bureau was not a stimulating context for Rossby, who, in 1928, became professor and head of the first department of meteorology in the United States at the Massachusetts Institute of Technology, Cambridge. At MIT, he made important contributions to the understanding of heat exchange in air masses and atmospheric turbulence. He also investigated oceanography to study the relationships between ocean currents and their effects on the atmosphere.

Rossby was given American citizenship in 1938. The following year, he became assistant chief of the Weather Bureau. In that capacity, Rossby was responsible for research and education and began his studies of the general circulation of the atmosphere. In 1941, he became chairman of the department of meteorology at the University of Chicago. Rossby carried out pioneering work on the upper atmosphere, proving how it affects the long-term weather conditions of the lower air masses. Measurements recorded with instrumented balloons had demonstrated that in high latitudes in the upper atmosphere there is a circumpolar westerly wind, which overlies the system of cyclones and anticyclones lower down. In 1940 Rossby developed the theory of wave movement in the polar jet stream. He demonstrated that long sinusoidal waves of large amplitude, now known as Rossby waves, are generated by perturbations caused in the westerlies by variations in velocity with latitude. Rossby also showed the importance of the strength of the circumpolar westerlies in determining global weather. When these are weak, cold polar air will sweep south, but when they are strong, they cause the normal sequence of cyclones and anticyclones. Rossby worked on mathematical models for weather prediction and introduced the Rossby equations, which, with the introduction of digital computers in the 1950s, were of fundamental importance to forecast the weather. During World War II, Rossby was in charge of training military meteorologists, and, at the end of the war, hired many of them to work in his department at the University of Chicago. Rossby served as president of the American Meteorological Society for 1944 and 1945, and laid the foundations for the Society's first scientific journal, the Journal of Meteorology.

Rossby and his Chicago Group were able to compile weather charts over periods of five to 30 days to extract the general features, and tried to analyze these using basic hydrodynamic principles. The group made radical simplifying suppositions, ignoring essential but transitory weather effects like the movements of water vapor and the dissipation of wind energy. Still, they began to conceptualize how large-scale features of the general circulation might arise from simple dynamical principles.

In 1950 Rossby returned to Sweden, but continued to visit the United States. In his home country, he worked with the Institute of Meteorology, which he founded in connection with the University of Stockholm. From 1954 to 1957 he was instrumental in arousing interest in atmospheric chemistry and the interaction of airborne chemicals with the land and the sea. On December 17, 1956, Rossby appeared on the cover of Time magazine and was praised for his key role in raising meteorology to the status of science. The piece also referred to a theory that Rossby was developing as a result of his interest in atmospheric chemistry. According to Rossby, the world's climate might be altered by solar heat trapped in the atmosphere due to a buildup of carbon dioxide. This was one of the first insights into the problem of global warming and paved the way for many researches in the field. Rossby was unable to fully develop this insight as he died on August 19, 1957, just nine months after the Time article.

The Carl-Gustav Rossby Research Medal is the highest award for atmospheric science presented by the American Meteorological Society for outstanding contributions to the understanding of the structure or behavior of the atmosphere. Rossby himself was the second recipient of this prestigious award when it was still called Award for Extraordinary Scientific Achievement.

sEE ALso: American Meteorological Society; Global Warming; Waves, Rossby.

BIBLioGRAPHY. David Laskin, "The Weatherman & the Millionaire: How Carl-Gustaf Rossby and Harry F. Guggenheim Revolutionized Aviation and Meteorology in America," Weatherwise (v.58/4, 2005); Spencer Weart, The Discovery of Global Warming (Harvard University Press, 2004).

Luca Prono University of Nottingham

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