A rogue wave is a single swell that is much higher than nearby waves, which can damage ships or coastal infrastructure. Ocean waves are among the most powerful natural forces on Earth, and as global trends suggest ocean winds will blow harder because of climate change, ocean waves could become more powerful. In new research, scientists from the University of Melbourne found that rogue waves emerge from strong wind forces and unpredictable waveform patterns, confirming an idea previously only demonstrated in lab experiments.
Toffoli et al. report direct observations of surface waves from a stereo camera system along with concurrent measurements of wind speed during an expedition across the Southern Ocean in the austral winter aboard the South African icebreaker S.A. Agulhas II. Image credit: Alessandro Toffoli.
“Rogue waves are colossi — twice as high as neighboring waves — that appear seemingly out of nowhere,” said University of Melbourne’s Professor Alessandro Toffoli, first author of the study.
Using state-of-the-art technology and embarking on an expedition to one of Earth’s most volatile oceanic realms, Professor Toffoli and colleagues deployed a novel technique for 3D imaging of ocean waves.
Operating stereo cameras aboard the South African icebreaker SA Agulhas II during the Antarctic expedition in 2017, they captured rare insights into the behavior of waves in this remote region.
Their method, mimicking human vision through sequential imaging, allowed the researchers to reconstruct the wavy ocean surface in three dimensions, providing unprecedented clarity into the dynamics of ocean waves.
The first scientific measurement of a rogue wave was the 25.6 m Draupner wave, recorded in the North Sea in 1995. Sixteen suspected rogue wave incidents have been reported in the 21st century.
“Antarctica’s choppy seas and wild winds can cause large waves to ‘self amplify,’ resulting in rogue wave frequency scientists had theorized for years, but could not yet verify in the ocean,” Professor Toffoli said.
Drawing upon numerical and laboratory studies, which had suggested the role of wind in the formation of rogue waves, the team’s observations have provided validation of these theories in the actual oceanic environment.
“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,” Professor Toffoli said.
“The wind creates a chaotic situation where waves of different dimensions and directions coexist.”
“Wind causes young waves to grow higher, longer and faster.”
“During this self-amplification, a wave grows disproportionately at the expense of its neighbors.”
“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.”
“This mirrors lab models: that sea conditions theoretically more prone to self-amplification produce more rogue waves.”
“In contrast, we detected no rogue waves in mature seas, which are not affected by wind.”
The authors emphasize the critical importance of integrating wind dynamics into predictive models for rogue wave forecasting.
“This shows that when developing tools for predicting rogue waves, scientists need to take wind into thorough consideration,” Professor Toffoli said.
The findings were published in the journal Physical Review Letters.
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A. Toffoli et al. 2024. Observations of Rogue Seas in the Southern Ocean. Phys. Rev. Lett 132 (15): 154101; doi: 10.1103/PhysRevLett.132.154101