Carl-Gustaf Arvid Rossby (Stockholm 28 December, 1898 – Stockholm 19 August, 1957) was a Swedish-US meteorologist who first explained the large-scale motions of the atmosphere in terms of fluid mechanics.

Born in Stockholm, Sweden, Rossby developed an interest in meteorology and oceanography while studying under Vilhelm Bjerknes at the University of Stockholm and University of Leipzig. In 1922, he returned to Stockholm to join the Swedish Meteorological Hydrological Service where he served as a meteorologist on a variety of oceanographic expeditions. While ashore between expeditions, he studied mathematical physics at the University of Stockholm.

In 1926, Rossby moved to the USA to join the U.S. Weather Bureau in Washington, DC. There, he combined theoretical work on atmospheric turbulence with the establishment of the first weather service for civil aviation. In 1928 he founded the first US department of meteorology at the Massachusetts Institute of Technology. His interests during this time ranges over atmospheric thermodynamics, mixing and turbulence and the interaction between oceans and atmosphere.

In 1938, he became a US citizen and the following year, assistant director of research at the U.S. Weather Bureau. His appointment as chair of the department of meteorology at the University of Chicago in 1940 began the period in which he turned his attention to large-scale atmospheric motions. He identified and characterised both the jet stream, and Rossby waves in the atmosphere.

During World War II, Rossby organised the training of military meteorologists, recruiting many of them to his Chicago department in the post-war years where he began adapting his mathematical description of atmospheric dynamics to weather forecasting by electronic computer. In 1947 he became founding director of the Institute of Meteorology in Stockholm, dividing his time between there and Chicago.

Between 1954 and his death in Stockholm in 1958 he championed and developed the field of atmospheric chemistry.

See also

• Rossby number
• Rossby radius of deformation
• Rossby wave