Big-wave science
Posted: Friday, May 12, 2006 9:57 PM by Alan Boyle
Take one scary phenomenon, find the worst conceivable real-world scenario and scale it up a few notches … that’s the formula for disaster flicks ranging from “10.5” to “Armageddon” to “The Day After Tomorrow,” and now for the “Poseidon” remake as well.
This week, the subject is rogue waves — giant walls of water that dwarf even your run-of-the-mill storm swells. These are distinct from the 33-foot-high, earthquake-generated tsunami waves we came to know all too well in 2004. For ages, mariners have told of much bigger midocean waves, rising more than 200 feet to hammer the ships caught in their sights.
The plot of "Poseidon" posits a 150-foot-high rogue wave, big and bad enough to upturn a cruise ship. Although that's way over the top — kind of like Shelley Winters' acting in the original 1972 "Poseidon Adventure" — it turns out that real-life rogue waves can come closer to that mark than scientists once thought.
Rogue waves, also known as freak waves, have been the subject of more studies in recent years, due to the availability of ocean-monitoring satellites. The European Space Agency says its MaxWave satellite radar project detected more than 10 rogue waves measuring higher than 82 feet (25 meters) over a three-week period in 2001 — perhaps including the 100-foot whoppers that smashed the windows of the cruise ships Caledonia and Bremen.
A 70-footer washed over the Norwegian Dawn cruise ship last year, a nearly-100-footer was reported in 2004 during Hurricane Ivan, and there have been reliable measurements of a 112-foot (34-meter) wave that rose over the USS Ramapo in 1933. Could there have been bigger waves that people didn't survive to tell about? Maybe so: In "The Bird in the Waterfall," Jerry Dennis and Glenn Wolff report that computer models can produce theoretical waves as high as 219 feet (67 meters).
The big mystery has to do with the mechanism that causes the waves. A variety of studies, including the MaxWave observations, have shown that cross currents can "focus" the energy of wind-driven waves through constructive interference.
"At some point, the waves all march in lockstep together, and then again they go their own way," Vijay Panchang, a maritime engineering expert at Texas A&M University in Galveston, told me today.
But sometimes freak waves can arise without those cross currents. "Sustained winds from long-lived storms exceeding 12 hours may enlarge waves moving at an optimum speed in sync with the wind," the ESA reported.
Seabed topography may play a role as well, Panchang said. A "bump" on the seafloor, for example, could give an extra boost to a wave at just the wrong time.
One of Panchang's biggest contributions to the science of big waves is to develop a forecasting model for coastal waves. Currently, the model is being applied to waves off the coast of Maine as well as the Gulf of Mexico and the Gulf of Alaska. You can check out the predictions here.
"Our predictions are reasonable," Panchang said — nothing like the whoppers of "Poseidon," but big enough to catch the attention of mariners and oil-platform operators.
For much, much more on the real science of freak waves, check out archived articles from Science News and Discover magazine — as well as this tutorial from the National Oceanic and Atmospheric Administration and this "Savage Seas" Web site from WNET. You can even play around with a virtual wave generator. Here's an interesting safety angle from the Boston Herald, just in time for the debut of the Freedom of the Seas. (Think "Poseidon" will ever play in that ship's theater?)
Meanwhile, for an intriguing discussion of where the physics goes wrong in "Poseidon," check out this blog discussion. If you spot any other scientific howlers from the film — or other summer blockbusters, for that matter — feel free to leave a comment.
