Freak Ocean Waves Are Created by Variations in Seafloor

Researchers of Florida State University have discovered that abrupt variations in the seafloor can cause dangerous waves in the ocean known as rogue or freak waves. These waves are so catastrophic that they were once thought to be the seafarers' imaginations figments.

Nick Moore, assistant professor of mathematics at Florida State, said that these are very huge waves which can cause massive destruction to ships or infrastructure, but they are not precisely understood. He is also an author of a new study on rogue waves and his study is published in the journal Physical Review Fluids, Rapid Communication.

These waves, once regarded as a myth, have stumped the scientific community for many decades. Researchers over the years across the world have analyzed a number of various factors which they thought might contribute to these waves, including wind excitation, the seafloor, and a phenomenon which is called Benjamin-Feir where deviations from a periodic waveform are reinforced by nonlinearity.

Most of the studies which aimed at the seafloor are considered only gentle slopes. Few studies which pushed the slopes to greater extremes relied primarily on the simulations of the computer.

Moore added that there was a relative underrepresentation of real-world data which you can get from laboratory experiments, where you can carefully control the different factors. Further, he said that often you need this real-world data to examine whether the computer simulations are giving you sensible predictions at all or not.

Laboratory experiments of Moore were the first to examine the effect of abrupt seafloor variations on wave statistics. Moore formed a long chamber with a variable bottom along with FSU's Geophysical Fluid Dynamics Institute Director Kevin Speer and now-former FSU student Tyler Bolles. The research team with the help of a motor for generating randomized waves, tracked thousands of waves to see if any patterns emerged.

The waves encountered a step in the bottom of the tank after they passed through several feet of a constant depth which shows an abrupt change in the seafloor. Moore along with his colleagues found that in the beginning, the waves appeared normal, following a traditional bell curve. But on passing over the step, the structures of the waves significantly changed. The altered waves followed a gamma distribution which is a mathematical function describing many patterns which defy the bell curve in a particular way.

The experiments and the emergence of this mathematical function have spurred new investigations into the origin of rogue waves.

By: Preeti Narula

Content: https://www.sciencedaily.com/releases/2019/02/190201114157.htm