I found this image on a website - returned as a HTTP error 404 'not found'.

But the clouds look strangely repetitive. At first I thought the image had been "photoshopped", but as @gerrit pointed out in a comment, each is different.

The sky locally is clear and blue, but there are clouds above the water in the distance.

Is this a real, recognizable type of formation? (the six repeated long, low clouds above the horizon in the distance) I have seen plenty of gravity wave cloud patterns in the sky and in the internet, but always from above, or below, never edge-on in a clear blue sky.

Image found here: http://wetlabs.com/sites/default/files/images/overboard.jpg

enter image description here

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    $\begingroup$ They're not exactly identical, or are they? Could be a combination of a gravity wave cloud and some imaging artefact. $\endgroup$
    – gerrit
    Mar 30, 2017 at 10:20
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    $\begingroup$ @gerrit I struggled with the title and introduction; and edit/improvement is welcome. I suppose I am just really interested if this is a side-view of a 'normal' gravity wave phenomenon. I've never seen such a view. Not really interested in the photoshop possibility. $\endgroup$
    – uhoh
    Mar 30, 2017 at 10:42
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    $\begingroup$ Could be evidence of a gravity wave in the atmosphere but also could be from onshore effects on the cloud layer. Without knowing the location would be difficult to tell. $\endgroup$
    – user824
    Dec 17, 2018 at 20:27
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    $\begingroup$ I've spent a while looking into the various mechanisms that typically produce wave and wave-like clouds, and I don't think the identification is possible with any real certainty just from the photograph, especially since that level is evidently barely exceeding condensation. It looks like it could be a weak manifestation of gravity waves, horizontal convective rolls, or even Kelvin-Helmholtz instability, but I wouldn't feel confident trying to pin down the identification from that level of cloudiness without other views or more knowledge of the environment. $\endgroup$
    – dplmmr
    Dec 19, 2018 at 17:46
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    $\begingroup$ @dplmmr wow, thank you for your analysis! I'd be happy to accept that as an answer if you posted it as one. If a short list of what it could be is the best possible answer, then that's the answer. Thanks! $\endgroup$
    – uhoh
    Dec 19, 2018 at 23:58

1 Answer 1


Identification of the phenomenon based solely on the photograph is unfortunately inconclusive, although several reasonable possibilities exist. While a wavelike structure is apparent, exact identification of the phenomenon is difficult due to the lack of cloud condensate (which would better illustrate the local vertical air motions ultimately driving cloud development) and of corresponding local weather observations (which could suggest which phenomenon is most likely to occur). Three possibilities seem most likely:


Horizontal Convective Rolls - a mode of convection in which clouds (and corresponding upward vertical air motion) preferentially organize in approximately linear lines, with downward vertical motion between (image from linked source). These clouds are observed over both land and water surfaces, although formation over water is more likely in cold weather when the water is relatively warm compared to land. This mode is possible, though perhaps least likely, given that weak clouds are visible across the horizontal length of the photograph - well-organized horizontal rolls commonly have clear air between the lines of cloud. (image source)


Gravity wave clouds - clouds that form in the upward motion regions of large-scale "waves" of vertical motion propagating through the atmosphere. Gravity waves are a common phenomenon occurring in many different atmospheric environments, with the resulting clouds varying greatly in appearance depending on the strength of the vertical motion and the amount of atmospheric moisture available for condensation. Given this, gravity wave clouds are a reasonable possibility based on the photograph. (image source)


Kelvin-Helmholtz wave clouds - An overturning motion that may develop at the interface between two atmospheric layers with substantially differing horizontal winds, with cloud condensation (assuming sufficient moisture) taking on an appearance similar to rolling ocean waves (image from linked source). This explanation also seems reasonable, given that air masses with distinct characteristics commonly occur in the lower atmospheric boundary layer and between ocean and land masses. Anecdotally, the clouds in the photograph look most visually similar to near-surface Kelvin-Helmholtz wave clouds I've seen, although again, the lack of actual cloud condensate makes this difficult to assess with any certainty. (image source)

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    $\begingroup$ This is an exemplary answer, thank you very much! I've slightly adjusted the title (only) to better direct traffic to it. $\endgroup$
    – uhoh
    Dec 20, 2018 at 3:04
  • $\begingroup$ Those waves have typically some physical scales associated with them, like a typical most-unstable wavelength for the Kelvin-Helmholtz instability. Maybe that would help to further distinguish those phenomena? $\endgroup$ Nov 21, 2019 at 8:22

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