Walter Heinrich Munk (born October 19, 1917) is an American physical oceanographer.
Born in Vienna, Austria, Munk was sent to a preparatory school in New York State in 1932. The family selected New York because they envisioned a career in finance for Munk in a New York bank with connections to the family business. His father, Dr. Hans Munk, and his mother, Rega Brunner, divorced when Munk was a child. His maternal grandfather was a prominent banker and Austrian politician, Lucian Brunner (1850-1914). His stepfather, Dr. Rudolf Engelsberg, was briefly a member of the Austrian government of President Engelbert Dollfuss.
Munk worked at the firm for three years and studied at Columbia University. He hated banking, and left the firm to attend the California Institute of Technology, where he earned a B.S. (1939) in physics. He applied for a summer job at the Scripps Institution of Oceanography. The next year the director of the Scripps, the distinguished Norwegian oceanographer Harald Ulrik Sverdrup, accepted him as a doctoral student, but told Munk that he did not know of a single job in oceanography which would become available in the next decade.
On June 20, 1953, Munk married Judith Horton. She was an active participant at the Scripps Institution of Oceanography for decades, where she made major contributions to architecture, campus planning, and the renovation and reuse of historical buildings. Judith Munk died on May 19, 2006.
Arguably Munk's best achievement is in showing rigorously why one side of the moon always faces the earth (Munk & McDonald, "The Rotation of the Earth", CUP, 1960; and later papers up to 1975). Lord Kelvin had also considered this question, and had fashioned a non-quantitative answer being roughly correct. It is due to the fact that the moon does not have a molten liquid core, and so cannot rotate through the egg-shaped distortion caused by the Earth's gravitational pull. Rotation through this shape requires internal shearing, and only fluids are capable of doing this with very small frictional losses. Thus the pointy end of the "egg" is gravitationally locked to always point directly towards the earth, with some small librations, or wobbles. Large objects may strike the moon from time to time, and may cause it to rotate about some axis, but it will quickly stop rotating. All frictional effects from such events will also cause the moon to regress further away from the earth.
Munk applied for American citizenship in 1939 after the Anschluss and enlisted in the ski troops of the U.S. Army as a private. This was unusual as all the other young men at Scripps joined the U.S. Naval Reserve. Munk was eventually excused from military service to undertake defense related research at Scripps. He joined several of his colleagues from Scripps at the U.S. Navy Radio and Sound Laboratory, where they developed methods related to amphibious warfare. Their methods were used successfully to predict surf conditions for Allied landings in North Africa, the Pacific theater of war, and on D-Day during the Normandy invasion.
Munk completed an M.S. in geophysics in 1940 and a Ph.D. in oceanography from the University of California, Los Angeles, in 1947. After graduation the Scripps Institution of Oceanography in La Jolla, California hired him as an assistant professor of geophysics. He became a full professor there in 1954.
He pioneered research on the relationship between winds and ocean circulation, coining the now widely used term "wind-driven gyres."
In the 1950s, Munk investigated irregularities in the Earth's rotation, such as the Chandler wobble and annual and long-term changes in the length of day (rate of the Earth's rotation), to see how these were related to geophysical processes such as the changes in the atmosphere, ocean, and core, and the energy dissipated by tidal acceleration. He also investigated how western boundary currents, such as the Gulf Stream, dissipated planetary vorticity. His inviscid theory of these currents did not have a time invariant solution; no simple solution to this problem has ever been found.
Starting in the late 1950s he returned to the study of ocean waves, and, thanks to his acquaintance with John Tukey pioneered the use of power spectra in describing wave behavior. This culminated with a study that he led in 1963 to observe waves generated by winter storms in the Southern Hemisphere and traveling thousands of miles throughout the Pacific ocean. To trace the path and decay of waves as they propagated northward, he established stations to measure waves from islands and at sea (on R/P FLIP) along a great circle from New Zealand to Alaska. The results showed little decay of wave energy with distance traveled.
Between 1965 and 1975 he turned to investigations of ocean tides, again bringing to bear modern methods of time-series analysis, and also developing deep-ocean pressure sensors that could be used to provide tidal data far from any land.
In 1968 he became a member of JASON, a panel of scientists who advised the U.S. government.
Beginning in 1975, Munk and Carl Wunsch of the Massachusetts Institute of Technology pioneered the development of acoustic tomography of the ocean. Munk developed the theory that by studying the sound propagation patterns and the time it takes for sound to travel through the oceans, it would be possible to detect important information about the ocean's large-scale structure. He thus conceived the Heard Island Experiment, in which acoustic signals were transmitted by instruments lowered 150 meters underwater near the remote island in the southern Indian Ocean. During four days in January 1991, in an experiment that has been called "the sound heard around the world," signals sent from Heard Island were received on the east and west coasts of the United States, as well as at many other stations around the world. The follow-up to this experiment was the Acoustic Thermometry of Ocean Climate (ATOC) project in the North Pacific Ocean.
In recent years Munk has worked on the role of tides in producing mixing in the ocean and on the relation between changes in ocean temperature, sea level, and transfer of mass between continental ice and the ocean.
His major works include The Rotation of the Earth: A Geophysical Discussion (with G.J.F. MacDonald, 1960) and Ocean Acoustic Tomography (with P. Worcester and C. Wunsch, 1995).
An interesting film documentary featuring Walter Munk was made in 1963. "Waves Across the Pacific" showcases his research on Antarctic storms and follows him and his fellow scientists as they track storm driven waves across the Pacific Ocean. The film features scenes of early digital equipment in use in field experiments with Munk's commentary on how unsure they were about using such new technology in remote locations.
Walter Munk was elected to the National Academy of Sciences in 1956 and to the Royal Society of London in 1976. He has been a both a Guggenheim Fellow (three times) and a Fulbright Fellow. He was also named California Scientist of the Year by the California Museum of Science and Industry in 1969. Among the many other awards and honors Munk has received are the Arthur L. Day Medal, from the Geological Society of America in 1956, the Sverdrup Gold Medal of the American Meteorological Society in 1966, the Gold Medal of the Royal Astronomical Society in 1968, the first Maurice Ewing Medal sponsored by the American Geophysical Union and the U.S. Navy in 1976, the Alexander Agassiz Medal of the National Academy of Sciences in 1977, the Captain Robert Dexter Conrad Award from the U.S. Navy in 1978, the National Medal of Science in 1985, the William Bowie Medal of the American Geophysical Union in 1989, and the Kyoto Prize (external link) in 1999.