<p>The image shown is a <a href="https://en.wikipedia.org/wiki/Lenticular_cloud" rel="noreferrer">lenticular cloud</a>, a type of cloud often observed around significant topographical features such as the mountain peaks shown in the photo. Depending on the local atmospheric moisture, they can occur on their own (as in this case), apart from other cloud features.</p>

<p>All cloud growth depends on the condensation of water resulting from air being cooled as it is <a href="https://www.ess.uci.edu/~yu/class/ess5/Chapter.6.cloud.all.pdf" rel="noreferrer">lifted vertically</a> by some forcing mechanism. However, these clouds are an exception to more typical cloud growth, which depends on the atmosphere having a tendency (or <a href="https://digitalatlas.cose.isu.edu/clima/imaging/clddev.htm" rel="noreferrer">instability</a>) for air to continue rising - and thereby condensing more liquid water - once forced upward.</p>

<p>Following the initial source cited above, lenticular clouds form in environments that are stable (i.e., not conducive) to these vertical motions, so upward motion is entirely driven by air forced over an obstacle - in this case, mountain terrain. From a horizontal view, the vertical motion forced by this obstacle commonly takes the form of a persistent wave pattern: <a href="https://i.sstatic.net/gfuKv.jpg" rel="noreferrer"><img src="https://i.sstatic.net/gfuKv.jpg" alt="orographic waves"></a> <a href="http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/lift_topo_wave.html" rel="noreferrer">image source</a></p>

<p>This occurs downwind of the terrain feature, with clouds forming over the portion of the wave featuring upwards vertical motion. This becomes extremely evident when viewing <a href="https://youtu.be/3P46yC6lma0?t=12" rel="noreferrer">time-lapse videos</a> of this phenomenon.</p>

CC BY-SA 4.0
2019-01-10T05:13:00.693Z
I was so fascinated by the cloud and distracted by the stars that didn't really notice the mountain in the photo until reading your answer. Yep, there it is! Thanks!
uhoh
CC BY-SA 4.0
2019-01-10T05:17:16.500Z
It's my favorite type of cloud, and a good example of how clouds are often indicators of some other mechanism at play, even subtle terrain features!
dplmmr
CC BY-SA 4.0
2019-01-10T22:42:26.983Z
A type of [Orographic clouds](http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/oth/org.rxml) that develop in response to the forced lifting of air by the earth's topography.
Keith McClary
CC BY-SA 4.0
2019-01-10T05:09:04.663Z
2019-01-10T05:09:04.663Z
dplmmr
<p>This <a href="https://twitter.com/esa_es/status/1080751887677378560" rel="noreferrer">tweet</a> from the European Space Agency (ESA)'s Spanish account show a striking photo of a round, flat, "space-ship-shaped" cloud in an otherwise completely clear sky. The stars are out so I assume this is at night, possibly with a Moon.</p>

<p>Could this be real? If so, what kind of cloud is it? and how can it appear out in the open?</p>

<p><a href="https://i.sstatic.net/dlMTp.jpg" rel="noreferrer"><img src="https://i.sstatic.net/dlMTp.jpg" alt="enter image description here"></a></p>

CC BY-SA 4.0
2019-01-10T08:28:11.923Z
For people in the northern hemisphere, the stars to the right of the cloud is what the constellation Orion looks like from the southern hemisphere.
Fred
CC BY-SA 4.0
2019-01-10T08:45:41.220Z
@gansub [hadn't even noticed](https://earthscience.stackexchange.com/questions/15922/what-is-this-spaceship-shaped-cloud?noredirect=1#comment32333_15923) the mountain, "...and how can it appear out in the open?" I know funny things happen at the tops of mountains but this (at first) seemed to come out of nowhere. Thanks!
uhoh
CC BY-SA 4.0
2019-01-10T08:48:42.833Z
Yes indeed, that's another reason I may have been [distracted](https://earthscience.stackexchange.com/questions/15922/what-is-this-spaceship-shaped-cloud?noredirect=1#comment32333_15923).
uhoh
CC BY-SA 4.0
2019-01-11T07:43:01.307Z
@gansub that crossed my mind for a sec but then I realized I have no way to even begin to estimate depth and height; it's hard for me to assert by myself that the two have anything to do with each other, but I suppose I could reference the answer here, and your linked Q&A above as sources for that.
uhoh
CC BY-SA 4.0
2019-01-28T02:10:41.737Z
@gansub I'm still thinking about this. Does the "Lee wave cloud" shown in the [diagram](https://i.sstatic.net/gfuKv.jpg) in [the answer](https://earthscience.stackexchange.com/a/15923/6031) pretty much answer without answering? Or do you think a new question and new answer are still possible?
uhoh
CC BY-SA 4.0
2019-01-29T16:13:44.167Z
@gansub Good additional info here and in your answer - I was worried about getting too specific without a good feel for height in this photo, as well as the wind direction and topography outside what's shown here.
dplmmr
<meteorology><clouds><orography>
What is this spaceship-shaped cloud?
uhoh
# What is this spaceship-shaped cloud?

(Asked by: username_0 on 2019-01-10)

This [tweet](https://twitter.com/esa_es/status/1080751887677378560) from the European Space Agency (ESA)'s Spanish account show a striking photo of a round, flat, "space-ship-shaped" cloud in an otherwise completely clear sky. The stars are out so I assume this is at night, possibly with a Moon.

Could this be real? If so, what kind of cloud is it? and how can it appear out in the open?

[![enter image description here](https://i.sstatic.net/dlMTp.jpg)](https://i.sstatic.net/dlMTp.jpg)

**Tags:** meteorology, clouds, orography

> **Comments:**
> **username_1**: For people in the northern hemisphere, the stars to the right of the cloud is what the constellation Orion looks like from the southern hemisphere.  
> **username_0**: @gansub [hadn't even noticed](https://earthscience.stackexchange.com/questions/15922/what-is-this-spaceship-shaped-cloud?noredirect=1#comment32333_15923) the mountain, "...and how can it appear out in the open?" I know funny things happen at the tops of mountains but this (at first) seemed to come out of nowhere. Thanks!  
> **username_0**: Yes indeed, that's another reason I may have been [distracted](https://earthscience.stackexchange.com/questions/15922/what-is-this-spaceship-shaped-cloud?noredirect=1#comment32333_15923).  
> **username_0**: @gansub that crossed my mind for a sec but then I realized I have no way to even begin to estimate depth and height; it's hard for me to assert by myself that the two have anything to do with each other, but I suppose I could reference the answer here, and your linked Q&A above as sources for that.  
> **username_0**: @gansub I'm still thinking about this. Does the "Lee wave cloud" shown in the [diagram](https://i.sstatic.net/gfuKv.jpg) in [the answer](https://earthscience.stackexchange.com/a/15923/6031) pretty much answer without answering? Or do you think a new question and new answer are still possible?  
> **username_2**: @gansub Good additional info here and in your answer - I was worried about getting too specific without a good feel for height in this photo, as well as the wind direction and topography outside what's shown here.  

---

## 1 answers

### Answer by username_2 on 2019-01-10. Score: 12 | Accepted answer

The image shown is a [lenticular cloud](https://en.wikipedia.org/wiki/Lenticular_cloud), a type of cloud often observed around significant topographical features such as the mountain peaks shown in the photo. Depending on the local atmospheric moisture, they can occur on their own (as in this case), apart from other cloud features.

All cloud growth depends on the condensation of water resulting from air being cooled as it is [lifted vertically](https://www.ess.uci.edu/~yu/class/ess5/Chapter.6.cloud.all.pdf) by some forcing mechanism. However, these clouds are an exception to more typical cloud growth, which depends on the atmosphere having a tendency (or [instability](https://digitalatlas.cose.isu.edu/clima/imaging/clddev.htm)) for air to continue rising - and thereby condensing more liquid water - once forced upward.

Following the initial source cited above, lenticular clouds form in environments that are stable (i.e., not conducive) to these vertical motions, so upward motion is entirely driven by air forced over an obstacle - in this case, mountain terrain. From a horizontal view, the vertical motion forced by this obstacle commonly takes the form of a persistent wave pattern: [![orographic waves](https://i.sstatic.net/gfuKv.jpg)](https://i.sstatic.net/gfuKv.jpg) [image source](http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/lift_topo_wave.html)

This occurs downwind of the terrain feature, with clouds forming over the portion of the wave featuring upwards vertical motion. This becomes extremely evident when viewing [time-lapse videos](https://youtu.be/3P46yC6lma0?t=12) of this phenomenon.

> **Comments:**
> **username_0**: I was so fascinated by the cloud and distracted by the stars that didn't really notice the mountain in the photo until reading your answer. Yep, there it is! Thanks!  
> **username_2**: It's my favorite type of cloud, and a good example of how clouds are often indicators of some other mechanism at play, even subtle terrain features!  
> **username_3**: A type of [Orographic clouds](http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/cldtyp/oth/org.rxml) that develop in response to the forced lifting of air by the earth's topography.  

---

