Stories of ships mysteriously sent to watery graves by sudden, giant waves have long puzzled scientists and sailors. New research by San Francisco State professor Tim Janssen suggests that changes in water depth and currents, which are common in coastal areas, may significantly increase the likelihood of these extreme waves.
Published in the Journal of Physical Oceanography, Janssen's wave model simulations show that focusing of waves by shoals and currents could increase the likelihood of a freak wave by as much as 10 times. Although scientists cannot predict the occurrence of individual extreme waves, Janssen's findings help pinpoint conditions and locations favorable for giant waves.
Extreme waves, also known as "freak" or "rogue" waves, measure roughly three times the size of the average wave height of a given sea state. Recorded monster waves have exceeded 60-feet -- the approximate size of a six-story building. Janssen's research suggests that in areas where wave energy is focused, the probability of freak-waves is much greater than previously believed.
Wave focal zones are particularly common in coastal areas where water depth variations and strong currents can result in dramatic focusing of wave energy. Such effects are particularly well known around river mouths and coastal inlets, restricting accessibility for shipping due to large, breaking waves near the inlet, or resulting in erosion issues at nearby beaches. Extreme examples of wave focusing over coastal topography include world-class surf spots, such as Mavericks and Cortez Banks in California. The identification of freak wave hot spots is also important for shipping and navigation in coastal areas, and the design of offshore structures.
"In a normal wave field, on average, roughly three waves in every 10,000 are extreme waves," Janssen said. "In a focal zone, this number could increase to about three in every 1,000 waves. In a focal zone, the average wave height is already increased due to the focusing of energy so that an extreme wave in such a high energy area can potentially be very energetic and dangerous."
Janssen's wave simulations estimated the evolution of waves in open oceans, waves interacting with an opposing current, and waves traveling over a topographical feature such as a reef. The simulations show that freely developing waves maintain normal statistical properties with a small likelihood of extremes. But when the waves are focused by variations in water depth or currents, the rapid increase in energy drives wave interactions that enhance the likelihood of extreme waves.
"We found that if the focusing is sufficiently strong and abrupt, wave interactions create conditions favorable to extreme waves," Janssen said. "When we gradually increase the focal strength, initially wave interactions are weak and statistics remain normal. However, when increasing the focal strength beyond a certain threshold, suddenly wave interactions are enhanced and freak waves are much more likely than normal. It appears that wherever waves undergo a rapid transformation, freak waves can be much more likely than we would otherwise expect."
Tim Janssen is an assistant professor of Geosciences at San Francisco State University. The paper is co-authored by T.H.C. Herbers of the Naval Postgraduate School in Monterey, Calif.
"Nonlinear wave statistics in a focal zone," will be published in the August issue of the Journal of Physical Oceanography, a journal of the American Meteorological Society.
Michael Bruntz | EurekAlert!
Climate change weakens Walker circulation
20.10.2017 | MARUM - Zentrum für Marine Umweltwissenschaften an der Universität Bremen
Shallow soils promote savannas in South America
20.10.2017 | Senckenberg Forschungsinstitut und Naturmuseen
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research