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The first stage of Windrows Forming
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Video Source: www.youtube.com/watch?v=WnH_AxsOiAo
Dommermuth et al. (2014) and Dommermuth (2020) show that windrows form due to the action of breaking waves. Foam, biological material, flotsam, and jetsam surf the fronts of breaking waves. The surfing action of the breaking waves scrubs the free surface clean like a wedge plow on a train clears snow. Each successive pass of a breaking wave increases the length of the windrows. This surfing mechanism differs from Langmuir (1938)’s original hypothesis that the “seaweed accumulated in streaks because of transverse surface currents converging toward the streaks.” There is a sweet spot for forming long rectilinear windrows whereby there is surfing followed by spilling of foam, flotsam, jetsam, etc. off to the sides of the whitecaps. Windrows are less likely to persist if the whitecaps are long crested. When whitecaps are too long transverse to the wind, successive passes of breaking waves tend to break up the windrows. Conversely, if whitecaps are too narrow transverse to the wind, there is no surfing to line up foam, flotsam, jetsam, etc. • This animation shows the start of windrows forming under the action of a spilling breaking wave. The free surface is seeded with Lagrangian particles. The Lagrangian particles surf the front of a breaking wave. Behind the front of white water, the free surface is scrubbed clean. Successive passes of spilling breaking waves form windrows. • The animations of windrows forming are periodically extended along the wind and transverse to the wind. As a result, the very initial formation of bands is visible. • The u-component of velocity surges forward. The v-component of velocity is asymmetrical. The v-component of velocity sweeps the particles to the sides of the spilling breaking wave. The velocity scales are normalized by the phase speed. • Dommermuth, D. G., Lewis, C. D., Tran, V. H., and Valenciano, M. A., “Direct Simulations of Wind- Driven Breaking Ocean Waves with Data Assimilation,” Proceedings of the 30th Symposium on Naval Hydrodynamics, Hobart, Tasmania, Australia, 2014. URL: http://tinyurl.com/y79sm9rp • Dommermuth, D. G., “Further Observations on how Wave Breaking Affects the Formation of Windrows,” ResearchGate preprint, oct 2020c. • URL: https://tinyurl.com/y3d5kwwv • Langmuir, I., “Surface motion of water induced by wind,” Science, Vol. 87, 1938, pp. 119–123. Thorpe, S., “Langmuir circulation,” Annual Review of Fluid Mechanics, Vol. 36, 2004, pp. 55–79.
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