When the ocean is still, i.e. there aren't waves that disturb the surface, you often see "lanes" of water that seem flat as opposed to areas where the wind causes ripples. What causes this?
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$\begingroup$ Has anyone considered that these flat streaks in the sea might be caused by some oily substance drifting along? $\endgroup$– Jim HurfordMay 2, 2022 at 14:07
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4 Answers
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There can be many reasons for the lines that you see where the water is not rippled.
1) There is no wind on those specific areas. Not likely in the photo used as the example but especially when there are cold fronts involved the wind can be very inconsistent over short horizontal distances.
2) You may be seeing the influence of boat wakes that passed over the area recently.
3) You may be seeing variation of the underlying ocean currents. Especially near the coast with tide changes there can be zones of significant ocean current. Wind and ocean currents have an influence on wave height and shape. When the wind blows against the current you get higher steeper waves. When you get wind blowing with the current you get shorter shallower waves (the smooth sections). The currents are not just horizontal but have vertical components as well. The lines identified could be vertical eddies in the current smoothing the surface whereas the smooth / rough line in the foreground is were the major ocean flow is going in opposite directions to each other.
4) If the coast in the foreground is shallow and there are waves coming to shore there then the lines identified to be rip currents caused by water returning from the coast line.
From my personal experience I would say that you are seeing variations in the surface ocean currents, and these currents change how the wind develops waves on the surface.
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1$\begingroup$ I think #3 is applicable in this case, since the lanes tend to be in the same place over time. $\endgroup$– user8389Jun 22, 2017 at 21:04
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1$\begingroup$ There's another possibility: the tidal wakes of bridge pilings, especially large suspension bridge towers. images.app.goo.gl/FydHAC8buTnZicga7 $\endgroup$– SpencerJun 20, 2020 at 19:51
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Expanding on Friddy's third point, this could be the surface signature of what are called internal waves (https://en.wikipedia.org/wiki/Internal_wave). The smooth regions indicate upward motion of internal waves and the rough regions indicate downward motion of internal waves. More information can be found here: http://www.whoi.edu/oceanus/feature/the-waves-within-the-waves
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$\begingroup$ Interesting...I knew about gravity waves I just never considered them internal to the water but when you consider the possibility of different water densities due to temperature or salinity it makes sense that subsurface wave, rather than mass movement, could cause observable surface features on the water. I will watch for this phenomenon in the future. $\endgroup$– user824Dec 21, 2017 at 18:29
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2$\begingroup$ Internal waves often visible in the atmosphere. They can be frequent in mountainous areas. An example, as seen from an airplane: physics.fullerton.edu/gwpac/news/highlights/… $\endgroup$– JohnDec 21, 2017 at 22:57
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$\begingroup$ Would I right in guessing that such waves would not be stationary? Or is there some way they can be more perpetual, caused by like coastline\floor terrain and current? $\endgroup$ Mar 11, 2021 at 4:28
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1$\begingroup$ @JeopardyTempest that is a good question. My knowledge on internal waves is focused on those caused by ocean tides over "rough" topography in the deep ocean. In that case, vertical motion will be sensitive to background stratification. Such waves have stationary and not stationary parts. As for what is shown in the photo, that could be caused by currents flowing over a bump. Depending on geometry/flow scales, they could be mostly stationary. $\endgroup$– JohnMar 11, 2021 at 19:40
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I have gone over these in a fishing boat many times. I often use this as a fish locator with some shoaling fish around the Uk. One side to the other does show a difference in water temps on the temp sensors fitted to the hull. It is my belief that these lanes are caused by differing temperature of water columns and an upwelling on the surface, between the 2 differing density of water. One being warmer than the other causes a density + temp fluctuation and the upwelling on collision. This upwelling caused the flat spots or lanes that can go for miles on times or maybe just a few hundred feet depending on the area at sea. Fish do tend to sit on one side or the other of these marks on the surface that appear dead flat and like river streams, flat on the sea surface apposed to the ripped water - They can be as wide as 20ft or more but often are no more than 10ft or less but are quite long and often going in one direction and then another. So i would say this is more to do with Currents - tidal movements of water and differing water temp columns. I would like to add - That salinity could also be part to play as many river pour into bay areas and i have overserved the flats spots during different stages of a tidal hight. Usually around top water when the water flows slow down some.
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1$\begingroup$ Yep +1, that's a nicely observed description of Langmuir rolls. They're generally driven by wind with temperature variations a consequence of the upwelling. Things you mention like currents, salinity have a big effect on where these rolls can form. $\endgroup$– DeditosMar 9, 2021 at 11:34
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$\begingroup$ This is great actual information compared to the guessing of many other answers. It would be really helpful to know if the water is colder in the upwelling or warmer compared to the surrounding water $\endgroup$– leafmealSep 20, 2022 at 15:13
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My guess is that it may be related to the currents, yes. I suppose that the change in color, is due to a slightly different viscosity of the waters at the lanes, which may affect the reflecting light. I think that if you could catch up swimming inside the lane, you would feel colder water.
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2$\begingroup$ You can improve your answer by adding some references and sources. $\endgroup$ Jun 20, 2020 at 17:46