After detailed observations of waves in the Southern Ocean, the factor that plays the key role in the formation of rogue waves was identified: The wind.
Rogue waves, or freak waves, are huge waves that can reach 30 meters and more. They appear out of nowhere and can be extremely dangerous to ships. For centuries, rogue waves were considered a sailor’s yarn until they were finally recognized as existing in 1995. However, almost 30 years later, researchers still do not agree on the mechanisms behind their formation.
A study published on April 12 in Physical Review Letters by an international research team led by Professor Alessandro Toffoli of the University of Melbourne now sheds light on the subject. The team found that wind is the main cause of these gigantic, unpredictable waves and that they occur more frequently than previously thought.
As wind speeds will continue to increase globally due to climate change, it can be expected that the ocean waves, which are among the strongest natural forces, will also become more powerful.
“Rogue waves are colossi – twice as high as neighbouring waves – that appear seemingly out of nowhere.”
Professor Alessandro Toffoli, University of Melbourne
The researchers’ expedition to the Southern Ocean on board the South African research vessel SA Agulhas II in 2017 provided the critical clues: Rogue waves arise from strong wind forces and unpredictable wave shapes. The observations confirm the team’s theory, which has so far only been proven in laboratory experiments.
The team developed a new technique to study the dynamics of ocean waves. Using two stereo cameras, the researchers were able to reconstruct the waves in three dimensions and gain an unprecedented insight into the behavior of waves.
“Antarctica’s choppy seas and wild winds can cause large waves to ‘self amplify,’ resulting in rogue wave frequency scientists had theorised for years, but could not yet verify in the ocean,” Professor Toffoli, lead author of the study, explained in a University of Melbourne press release. “Our observations now show that unique sea conditions with rogue waves arise during the ‘young’ stage of waves – when they are most responsive to wind. This suggests wind parameters are the missing link.”
He goes on to explain that the wind creates a chaotic situation in which waves of different sizes and directions coexist. The wind causes young waves to become higher, longer, and faster and to grow disproportionately at the expense of their neighbors in a self-reinforcing mechanism.
“We show young waves display signs of self-amplifying and more likelihood of becoming rogue because of the wind. We recorded waves twice as high as their neighbours once every six hours,” Professor Toffoli said. In mature seas that were not influenced by the wind, however, the team was unable to detect any rogue waves, according to Professor Toffoli.
The first scientifically recorded rogue wave was the 25.6 meter high Draupner wave in the North Sea in 1995. Numerous ships have already been severely damaged by rogue waves, some of which sank. Several cruise ships have also been hit by rogue waves, including the MS Bremen in 2001 and the Viking Polaris in 2022, both in the South Atlantic. The latter incident resulted in one fatality and four injuries.
A lot more research will be needed before rogue waves can be predicted with a reasonable degree of reliability. However, with the current study and the finding that wind dynamics must be included in the models, science has come a great deal closer to achieving this.
Julia Hager, Polar Journal AG
