Faculty of Mathematics and Natural Sciences

Predicting “freak waves”

Yan Li, an associate professor at the Department of Mathematics and Bjerknes Centre for Climate Research, has been working on developing theoretical models to predict the occurrence probability of so-called “rogue waves” or “freak waves.” These waves can be approximately three times higher than the average wave height and are extremely dangerous for ships and other marine operations.

Yan Li by the shore in Bergen, known as "the capital of the fjords".
Yan Li by the shore in Bergen, known as "the capital of the fjords".
Eivind Senneset

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Inside her office on the fourth floor of the Realfagbygget at the University of Bergen, Yan Li sits in front of her computer screen, pointing with fascination to a black-and-white image of a cargo ship near the Bay of Biscay, facing a giant wave. This wave resembles the famous Hokusai painting “The Great Wave off Kanagawa”.

Under the Wave off Kanagawa, Katsushika Hokusai

Under the Wave off Kanagawa (Kanagawa oki nami ura), also known as The Great Wave, from the series Thirty-six Views of Mount Fuji (Fugaku sanjūrokkei)

Katsushika Hokusai/Metropolitan Museum

Such freak waves appear out of nowhere and are much higher than the surrounding average waves. They are neither tsunamis or tidal waves, and are not triggered by earthquakes or landslides. Until now, nobody can say for sure how they originate. But Li has developed a model which undiscovers a possible cause for the formation of these awe-inspiring waves.

Li moved from Shanghai to Bergen to study these mysterious waves. It is here, off the coast of Norway and south of Iceland, that the world’s highest waves occur. As an example, she mentions the wave that hit the unmanned Norwegian Draupner platforms in the North Sea on New Year’s night in 1995.

BBC2 Horizon Freak Wave

“It was just like a mountain, a wall of water coming against us”: On YouTube, there is an episode of the BBC documentary series Horizon from 2002, where the giant wave that hit Draupner is reconstructed, and experienced sailors share their experiences with the freak wave.

BBC2 Horizon Freak Wave

The wave was measured by Statoil at 25.6 meters, making it the highest individual wave ever recorded by a fixed installation – equivalent in size to a nine-story building. This giant wave accelerated research into this previously unexplained mystery, and it is in the wake of this that Li conducts her pioneering research.

- Ocean surface coversmore than 70% of the Earth’s surface, and surface waves are everywhere. It struck me: How come oceanographers tend to neglect the effect of surface waves? This realization led me to understand that we actually need a better model that considers in addition current, turbulence, and wind, says Yan Li.

She noticed this research topic during her master’s studies at the Science School of Naval Architecture, Ocean, and Civil Engineering (NAOCE) at Shanghai Jiao Tong University (SJTU). There, she studied the effects of extreme wave events on offshore structures, realizing that her work had the potential to predict the occurrence of extremely large waves. Her work did not go unnoticed, as she received an award as an outstanding young researcher from the Chinese Ministry of Knowledge.

Pioneering wave research

- While current models are based on a flat ocean surface, the OceanCoupling model I am developing is the first to consider a more moving ocean surface, because this it obeys the nature of our open oceans. Essentially, it focuses on modeling the crucial physical processes in the atmosphere-wave-current coupling, she explains.

With the OceanCoupling project, Li introduces a new and paradigm shifting method which permits us to both physically resolve the extreme wave events and their coupling with large-scale ambient environment like the ocean circulation. This can only be made possible by an explicit coupling within a Wave-Current-Atmosphere (WCA) system. Such a method is a crucial next step as local extreme wave events are higly relevant to oceonographers, as is reported in her most recent work.

Freak wave illustration by Yan Li

Extremely large sea waves and Langmuir circulations are fascinating natural phenomena, having attracted the attention of wave modelers and oceanographers for many years. However, do you know their occurrence might be physically connected? Yan Li's new publication in Geophysical Research Letters, made in collaboration with Amin Chabchoub, explains how and why. For more details, check out the new paper with open access through https://lnkd.in/d29YskFj

Yan Li

OceanCoupling simply initiates a new way of efficiently modeling complex systems with multiple scales, offering insights applicable to fluid dynamics and similar physical phenomena. Li has made an initial breakthrough by proposing a novel approach and she is eager to exploring the potential of this approach in modeling the more complex WCA system.

We are entering a critical period for sustainable ocean development and net-zero emissions. Both aspects have stimulated rapid growth in innovative technologies to meet our need for renewable energy and large international monitoring projects for the oceans.

Initially, Li is developing the model to create a product that can be useful for geophysicists, oceonographers and others seeking better calculations. OceanCoupling project will provide more reliable data by monitoring events. The project’s outcomes will provide timely links to ocean surface remote sensing products that monitor the ocean surface and will equip us with a feasible tool to tackle the ever-increasing wave extremes due to climate changes and innovative technologies for renewable energy.

For instance, this insight can be used to optimize turbine performance and safety in developing offshore wind farms. Li also aims to collaborate with major ongoing projects such as NASA and CNES’s satellite project, The Surface Water and Ocean Topography mission (SWOT), which monitors the ocean surface. Their goal is to achieve millimeter-level precision.

- My model can contribute valuable input in this context. We can monitor events in real time and use the models to provide feedback to such projects, says Li.

Yan Li at the tip of Nordnes, Bergen.
Eivind Senneset

Higher, steeper, more frequent

Rogue waves occur in two forms: individually or as “three sisters.” These enormous waves can cause serious consequences such as death and significant destruction. Concern is growing about how climate change may lead to increasingly higher, steeper, and more frequent waves.

- An important point to note is that when we talk about extreme weather, people think of cold waves or heatwaves, or extreme weather conditions like heavy rain. But it also means that ocean waves can become steeper, and also the rogue wave events also can become even more frequent. This hasn’t received as much attention as it should, so I’d really like to raise this point to the public, says Li.

Researching in Bergen

She was hired at the University of Bergen in 2021, following a period working at Norwegian University of Science and Technology (NTNU) and the University of Oxford. Her daily work involves teaching and advising a group of master’s and doctoral students. She looks forward to establishing her own research group and is in the process of hiring a doctoral candidate to work on the interaction between waves and ocean currents.

- I deeply value the research freedom and collaborative work environment here. Professor Simen A. Ådnøy Ellingsen, my supervisor, has greatly inspired me to work in this field and has treated me as a colleague from day one. The support from the research community is invaluable, bolstering my research efforts, says Yan Li.

Yan Li in front of a chalk-written equation on the blackboard.
Eivind Senneset