RIP Walter Munk, The Grandfather of Wave Forecasting

Tony Butt

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Updated 7d ago

Professor Walter Munk, ‘The Grandfather of Wave Forecasting’, arguably the greatest oceanographer who ever lived, passed away on February 8 2019 at the age of 101.

You may not have heard of Walter Munk. That is, unless you have ever read anything about surf science or wave forecasting, in which case his name will be more than familiar. If, like me, you happen to have studied oceanography on a more serious basis, there is a good chance that Munk’s discoveries will have inspired some of your own work.

Munk was born in 1917, in Vienna, Austria. His parents divorced when he was a child and in 1932 he moved to New York. His grandfather had been a prominent banker, and the family had ties to the New York banking world, where he worked for three years. But he hated it, and ended up studying physics at the California Institute of Technology, where he graduated in 1938. He then got a summer job at the Scripps Institution of Oceanography, and was accepted for a PhD under the legendary Norwegian oceanographer, Harald Sverdrup.

With the rise of the Nazis in Europe and the imminent onset of World War II, Munk obtained U.S. citizenship in 1939, and started working with the U.S. Navy Radio and Sound Laboratory, developing methods for amphibious invasions.

While observing training sessions for amphibious landings in South Carolina, he noticed that the waves were severely interfering with the landing craft as they tried to get onto the beach. Munk convinced Sverdrup to help him develop a method for predicting surf conditions so that allied invasions could have a better chance of succeeding. The Sverdrup and Munk wave prediction technique worked so well that it was used in the 1944 D-Day landings at Normandy, the largest naval invasion in history.

This was, of course, also the first time anybody had devised a way to predict surf, and it paved the way for the research over the following decades that led to the models we all use nowadays. In fact, if it wasn’t for Walter Munk, MSW might not even exist.

His work influenced many thousands of scientists and, of course, most surfers throughout the world

In 1947, after all the distractions of World War II were over, he obtained his PhD, and continued to make more ground-breaking discoveries in oceanography. In 1953 he married artist and designer Judith Horton, who worked on the restoration of historical buildings at Scripps. In 1954 he became a full professor of geophysics at Scripps, and continued to work there until his death. In 2006 his wife Judith died aged 81, and in 2011 he married Mary Coakley, who continues to run the Walter Munk Foundation for the Oceans.

Walter Munk never retired; he kept working as Professor of Geophysics at Scripps Institute until the day he died.

Munk truly was the ‘Grandfather of Wave Forecasting’. After his seminal work during World War II, he continued his research on wave prediction techniques, with Harald Sverdrup and later with coastal engineer Charles Bretschneider.

Around the late 1940 and early 1950s they developed a really elegant way to predict the waves using the technology available at the time. It was an empirical model, based on hundreds of observations of the resulting wave heights and periods in different combinations of the strength of the wind, the distance over which that wind blows (fetch) and the duration of time it blows. The model comprises a set of equations through which you can calculate the wave height and period by inputting values of windspeed, fetch and duration. It is called SMB theory, after its inventors. Crucially, it laid down the foundations for the research that led to the sophisticated models we all use nowadays.

He made some of the first observations of wave grouping (sets) decades before most people knew anything about surfing. Closely related, he was the first to study those long, tsunami-like surges of water that hit the coast during large swells and storms and that we now know are so important for coastal erosion. He was the first to name them: infragravity waves.

He made some ground-breaking discoveries about the propagation of oceanic swell. In 1963, he headed a group of scientists from Scripps in a fascinating experiment to track swells. They set up a system of six wave-measuring stations in the Pacific over a 10,000-km great-circle route between New Zealand and Alaska. They tracked 12 major swell events from storms in the Southern Ocean all the way up to Alaska. One of the most important findings of that seminal experiment was that the total wave energy in long-travelled swells is attenuated very little. Also, the changing signature of the swell as it progressively arrived at each point clearly demonstrated how the longer-period waves in a swell gradually outrun the short ones – a principle called radial dispersion. All these details and more are explained in the classic film Waves Across the Pacific.

Munk also did revolutionary work on many other subjects, not just wave forecasting. He studied the way winds drive oceanic currents and was the first to coin the term ‘wind-driven gyres’ – those same circulating vortices that most of us now associate with plastic pollution. He made important tidal measurements using pressure sensors on the deep-ocean floor. And he even helped to prove why the same side of the Moon always faces the Earth due to a phenomenon called tidal locking; in other words why there is a Dark Side of the Moon. He investigated the use of sound propagation to estimate large-scale temperature variations of the ocean, based on the fact that sound travels faster in warm water than in cold, decades before we grasped the urgency of ocean warming due to man-made climate change.

Walter Munk’s amazing career, spanning over eight decades, was like several lifetimes of work for a normal scientist. He was there, almost from the beginning of oceanography itself, right up to the present day. His work influenced many thousands of scientists and, of course, most surfers throughout the world.