A Skoltech researcher has developed a theoretical model of wave formation in straits and channels, which takes into account nonlinear effects in the presence of a coastline. This research will improve forecasting of water waves, make sea travel safer, and protect coastline infrastructure. Article published in Ocean Dynamics magazine.
Predicting surface weather at sea has always been a challenge with very high stakes. For example, more than 4,000 people died in a storm at sea during Operation Overlord in Normandy in June 1944. An inaccurate forecast of the situation at sea changed the course of the military operation. Current wave forecasting models, such as those used by NOAA (National Oceanic and Atmospheric Administration) in the United States, are imperfect. That being said, they have many configurable parameters to provide a reasonably good forecast.
However, as noted in his article by a senior researcher at Skoltech and the Physics Institute. P.N. Lebedev Institute of RAS Andrey Pushkarev, coastlines complicate the situation. The fact is that forecasting disturbances in the English Channel is almost as difficult today as it was in 1944. Research by the Russian scientist shows that the behavior of waves in channels or straits will differ significantly from the behavior of waves in the open sea.
“Shorelines create an inhomogeneity – the gradient of the wave energy distribution between its zero value at the boundary and non-zero value on the shore. This gradient triggers the advection of waves, which, as a result, leads to special effects of wave generation, orthogonal to the wind, ”explains Pushkarev.
The specific conditions of the channels and straits make it possible to accurately solve the Hasselman equation. It describes wave behavior close to single-current models. However, it is still impossible to solve with modern computers. Pushkarev’s theoretical modeling of wave formation in a strait resembling the English Channel showed that the development of turbulence did not correspond to the predictions of traditional models. The point is that the structure of turbulence was significantly different due to nonlinear interactions and advection of waves. Since the observed phenomenon has some similarities to laser radiation, it is called the Nonlinear Ocean Wave Amplifier or NOWA.
The shores of the strait play the role of semi-reflecting mirrors for the generated waves.
The new model, using an exact version of the Hasselman equation, shows that existing operational wave weather forecasting models do not account for this effect, considering reflections to be more of an artifact.
The generation of waves perpendicular to the wind similar to the laser effect can be observed not only in straits, but also in the open sea with specific inhomogeneous winds. There, spatial wind turning points create conditions similar to those observed in a body of water with shores.
The new study promises to explain the nature of seiches, the kind of standing waves in semi-enclosed bodies of water that pose a big problem for ships in ports. They are called “murderous” because of their destructive effect. But it also suggests that properly describing turbulence in the presence of a coastline will allow for rogue waves, seemingly unpredictable surface waves that are extremely dangerous even for large ships.