Harald Ulrik Sverdrup (15 November 1888 – 21 August 1957) was a Norwegian oceanographer and meteorologist who made a number of important theoretical discoveries in these fields. Having first worked in Bergen and Leipzig he was the scientific director of the North Polar expedition of Roald Amundsen aboard the Maud from 1918 to 1925. His measurements of bottom depths, tidal currents, and tidal elevations on the vast shelf areas off the East Siberian Sea correctly described the propagation of tides as Poincare waves. Upon his return from this long expedition exploring the shelf seas to the north of Siberia, he became the chair in meteorology at the University of Bergen in Norway.
He was made director of California's Scripps Institution of Oceanography in 1936, initially for 3 years but the intervention of World War II meant he held the post until 1948. During 33 expeditions with the research vessel E. W. Scripps in the years 1938-1941 he produced a detailed oceanographic dataset off the coast of California. He also developed a simple theory of the general ocean circulation postulating a dynamical vorticity balance between the wind-stress curl and the meridional gradient of the Coriolis parameter Sverdrup balance. This balance describes wind-driven ocean gyres away from continental margins at western boundaries. After leaving SIO, he returned home to become director of the Norwegian Polar Institute and continued to contribute to oceanography, ocean biology and polar research. In biological oceanography, his Critical Depth Hypothesis published in 1953 was a significant milestone in the explanation of phytoplankton spring blooms.
His many publications include the magnum opus The Oceans: Their Physics, Chemistry and General Biology by Harald Sverdrup, Martin W. Johnson and Richard H. Fleming (1942, new edition 1970) which formed the basic curriculum of oceanography for the next 40 years around the world.
He was a member of the American and Norwegian Academies of Science and the Swedish Order of the Polar Star. The sverdrup (Sv) is used in physical oceanography as an abbreviation for a volume flux of one million cubic meters per second. The American Meteorological Society's named the Sverdrup Gold Medal Award in his honor as well.