Jacob Aall Bonnevie Bjerknes was a Norwegian-American meteorologist. Jacob Aall Bonnevie Bjerknes was born in Stockholm, Sweden, in 1897. During the 1920s and 1930s, in addition to his studies of cyclones, he gathered data on the structure of low-pressure centres and conducted research on the dynamics of atmospheric convection. In 1939 Bjerknes moved to the United States and the next year became professor of meteorology at the University of California, Los Angeles. After World War II his studies chiefly concerned atmospheric circulation. In 1952 he utilized photographs taken by high-altitude research rockets for weather analysis and forecasting and was thus among those who initiated the use of space-age techniques for meteorological research. In later work he discovered relationships between Pacific Ocean temperatures and North American weather. The American Geophysical Union honored Bjerknes’ pathbreaking work in meteorology in 1945 with the William Bowie Medal, its highest award, recognizing fundamental contributions to geophysics and the AGU principle of unselfish cooperation in research. Additional honors included the American Meteorological Society’s Rossby Medal (1960) and the National Medal of Science (1966). Bjerknes died in 1975.